VMMs / Hypervisors
Intel Corporation
21 July 2008
Agenda
-
Xen internals
-
-
High level architecture
Paravirtualization
HVM
Others
-
KVM
VMware
OpenVZ
INTEL CONFIDENTIAL
Xen Overview
INTEL CONFIDENTIAL
Xen Project bio
•
Xen project was created in 2003 at the University of Cambridge Computer Laboratory in
what's known as the Xen Hypervisor project
–
–
•
•
•
Led by Ian Pratt with team members Keir Fraser, Steven Hand, and Christian Limpach.
This team along with Silicon Valley technology entrepreneurs Nick Gault and Simon Crosby founded XenSource
which was acquired by Citrix Systems in October 2007
The Xen® hypervisor is an open source technology, developed collaboratively by the Xen
community and engineers (AMD, Cisco, Dell, HP, IBM, Intel, Mellanox, Network
Appliance, Novell, Red Hat, SGI, Sun, Unisys, Veritas, Voltaire, and of course, Citrix)
Xen is licensed under the GNU General Public License
Xen supports Linux 2.4, 2.6, Windows and NetBSD 2.0
INTEL CONFIDENTIAL
Xen Components
A Xen virtual environment consists of several modules that provide the virtualization
environment:
• Xen Hypervisor - VMM
• Domain 0
• Domain Management and Control
• Domain User, can be one of:
–
–
Paravirtualized Guest: the kernel is aware of virtualization
Hardware Virtual Machine Guest: the kernel runs natively
Domain 0
Domain
Management
and Control
Domain U
Domain U
Paravirtual
Guest
Domain
U
Paravirtual Guest
Paravirtual Guest
Hypervisor - VMM
INTEL CONFIDENTIAL
Domain U
Domain U
HVM
Guest U
Domain
HVM Guest
HVM Guest
Xen Hypervisor - VMM
The hypervisor is Xen itself.
It goes between the hardware and the operating systems of the various domains.
The hypervisor is responsible for:
• Checking page tables
• Allocating resources for new domains
• Scheduling domains.
• Booting the machine enough that it can start dom0.
It presents the domains with a VirtualMachine that looks similar but not identical to the native
architecture.
Just as applications can interact with an OS by giving it syscalls, domains interact with the
hypervisor by giving it hypercalls. The hypervisor responds by sending the domain an
event, which fulfills the same function as an IRQ on real hardware.
A hypercall is to a hypervisor what a syscall is to a kernel.
INTEL CONFIDENTIAL
Restricting operations with Privilege Rings
The hypervisor executes privileged instructions, so it must be in the right place:
• x86 architecture provides 4 privilege levels / rings
• Most OSs were created before this implementation, so only 2 levels are used
• Xen provides 2 modes:
–
–
In x86 the applications are run at ring 3, the kernel at ring 1 and Xen at ring 0
In x86 with VT-x, the applications run at ring 3, the guest at ring non-root-0 and Xen at ring root-0 (-1)
Native
3
Paravirtual x86
3
HVM x86
The Guest is moved to
ring 1
3
1
0
Applications
Guest kernel (dom0 and dom U)
Hypervisor
INTEL CONFIDENTIAL
0
0
The Hypervisor is moved to
ring -1
Domain 0
Domain 0 is a Xen required Virtual Machine running a modified Linux kernel with special
rights to:
• Access physical I/O devices
–
Two drivers are included in Domain 0 to attend requests from Domain U PV or HVM guests
• Interact with the other Virtual Machines (Domain U)
• Provides the command line interface for Xen daemons
Due to its importance, the minimum functionality should be provided and properly secured
Some Domain 0 responsibilities can be delegated to Domain U (isolated driver domain)
Domain 0
PV
Network backend
driver
Block backend
driver
Communicates directly with the local
networking hardware to process all virtual
machines requests
Communicates with the local storage
disk to read and write data from the drive
based upon Domain U requests
HVM
Qemu-DM
INTEL CONFIDENTIAL
Supports HVM Guests for networking
and disk access requests
Domain Management and Control Daemons
The Domain Management and Control is composed of Linux daemons and tools:
•
Xm
–
•
Xend
–
•
A C library that allows Xend to talk with the Xen hypervisor via Domain 0 (privcmd driver delivers the request to
the hypervisor)
Xenstored
–
•
Python application that is considered the system manager for the Xen environment
Libxenctrl
–
•
Command line tool and passes user input to Xend through XML RPC
Maintains a registry of information including memory and event channel links between Domain 0 and all other
Domains
Qemu-dm
–
Supports HVM Guests for networking and disk access requests
INTEL CONFIDENTIAL
Domain U – Paravirtualized guests
The Domain U PV Guest is a modified Linux, Solaris, FreeBSD or other UNIX system that is
aware of virtualization (no direct access to hardware)
No rights to directly access hardware resources, unless especially granted
Access to hardware through front-end drivers using the split device driver model
Usually contains XenStore, console, network and block device drivers
There can be multiple Domain U in a Xen configuration
Domain U - PV
Console driver
XenStore driver
Network front-end
driver
Block front-end driver
INTEL CONFIDENTIAL
Similar to a registry
Communicates with the Network
backend driver in Domain 0
Communicates with the Block
backend driver in Domain 0
Domain U – HVM guests
The Domain U HVM Guest is a native OS with no notion of virtualization (sharing CPU time
and other VMs running)
An unmodified OS doesn’t support the Xen split device driver, Xen emulates devices by
borrowing code from QEMU
HVMs begin in real mode and gets configuration information from an emulated BIOS
For an HVM guest to use Xen features it must use CPUID and then access the hypercall
page
Domain U - HVM
Xen virtual firmware
INTEL CONFIDENTIAL
Simulates the BIOS for the unmodified
operating system to read it during startup
Pseudo-Physical to Memory Model
In an operating system with protected memory, each application has it own
address space. A hypervisor has to do something similar for guest operating
systems.
Virtual
…
Application …
Kernel
…
…
Pseudo-physical
Hypervisor
…
…
Machine
The triple indirection model is not necessarily required but it is more convenient
from the performance point of view and modifications needed in the guest kernel.
If the guest kernel needs to know anything about the machine pages, it has to
use the translation table provided by the shared info page (rare)
Software and Solutions Group
INTEL CONFIDENTIAL
12
Pseudo-Physical to Memory Model
There are variables at various places in the code identified as MFN, PFN, GMFN and
GPFN
PFN (Page Frame Number)
It means “some kind of page frame
number”. The exact meaning
depends on the context
MFN (Machine frame number)
Number of a page in the (real)
machine’s address space
GPFN (Guest page frame number)
These are page frames in the guest’s
address space. These page
addresses are relative to the local
page tables
GMFN (Guest machine frame
number)
This refers to either a MFN or a
GPFN, depending on the
architecture
Software and Solutions Group
INTEL CONFIDENTIAL
13
Virtual Ethernet interfaces
Xen creates, by default, seven pair of "connected virtual ethernet interfaces" for use by dom0
For each new domU, it creates a new pair of "connected virtual ethernet interfaces", with one
end in domU and the other in dom0
Virtualized network interfaces in domains are given Ethernet MAC addresses (by default xend
will select a random address)
The default Xen configuration uses bridging (xenbr0) within domain 0 to allow all domains to
appear on the network as individual hosts
INTEL CONFIDENTIAL
The Virtual Machine lifecycle
Xen provides 3 mechanisms to boot a VM:
- Booting from scratch (Turn on)
- Restoring the VM from a previously saved state (Wake)
- Clone a running VM (only in XenServer)
PAUSED
Stop
Resume
Start
Pause
(paused
) Turn on
OFF
RUNNING
Turn off
Wake
Turn off
SUSPENDED
INTEL CONFIDENTIAL
Sleep
Migrate
A project: provide VMs for instantaneous/isolated
execution
Goal: determine a mechanism for instantaneous execution of applications in sandboxed VMs
Approach:
• Analyze current capabilities in Xen
• Implement a prototype that addresses the specified goal: VM-Pool
Technical specification of HW and SW used:
• Intel® Core™ Duo T2400 @ 1.83GHz 1828 MHz
• Motherboard Properties
–
–
•
•
Motherboard ID: <DMI>
Motherboard Name: LENOVO 1952D89
2048 MB RAM
Software:
–
–
–
Linux Fedora Core 8 Kernel 2.6.3.18
Xen 3.1
For the Windows images Windows XP SP2
INTEL CONFIDENTIAL
Analyzing Xen spawning mechanisms
•
Booting from scratch
# of CPU
Time
# of CPU
Time
1
93.5 sec
1
19.5 sec
2
79 sec
2
22 sec
HVM WinXP varying the
#CPU
• Restoring from a saved state
VM RAM
Size
•
Image in Hard Disk
Image in RAM
Disk
256 MB
16 sec
13 sec
512 MB
21 sec
15 sec
HVM WinXP 4GB disk /
1CPU
Cloning a running VM
Image size
Time
2 GB
145 sec
4 GB
220 sec
8 GB
300 sec
HVM WinXP 4GB disk / 1CPU
INTEL CONFIDENTIAL
PV Fedora 8 varying the
#CPU
VM RAM
Size
HDD
RAM disk
256 MB
15 sec
9 sec
512 MB
23 sec
16 sec
1024 MB
37 sec
29 sec
PV Fedora 8 varying the #CPU
Dynamic Spawning with a VM-Pool
•
•
To have a pool of virtual machines already booted and ready for execution, but in a
“paused” state
These virtual machines keep their RAM but they don’t use processor time, interrupts
and other resources
Simple interface defined:
• get: retrieves and unpauses a virtual machine from the pool
• release: gives back a virtual machine to the pool and restarts the VM
High level description:
VM Pool
Set of free Virtual Machines
VM1
External interface
to listen for
requests
VM2
VM3
VM Pool
Manager
VMM
INTEL CONFIDENTIAL
VM4
Results with the VM-Pool
•
The VM is ready to run in less than half a second (~350 milliseconds)
Initialization time - from scratch
Initialization time - resume
Get operation
seconds
52±1
seconds
341
Release operation - from scratch
Release operation - resume
milliseconds
110±21
seconds
30±2
seconds
Preferred spawning method is resuming, although it uses additional disk storage
VMPool Initialization Time
300
250
200
S
e
c
o
n
d
s
•
265±21
From
scratch
150
Resume
100
50
0
VM Booting Mode
INTEL CONFIDENTIAL
Virtual Machines Scheduling
The hypervisor is responsible for ensuring that every running guest receives some CPU time.
Most used scheduling mechanisms in Xen:
• Simple Earliest Deadline First – SEDF (being deprecated):
–
•
Each domain runs for an n ms slice every m ms (n and m are configured per-domain)
Credit Scheduler:
–
–
–
–
–
Each domain has a couple of properties: a cap and a weight
Weight: determines the share of the physical CPU time that the domain gets, weights are relative to each other
Cap: represents the maximum, it’s an absolute value
Default work-conserving; if no other VMs needs to use CPU, then the running one will be given more time to
execute
Uses a fixed-size 30ms quantum, and ticks every 10 ms
Xen provides a simple abstract interface to schedulers:
struct scheduler {
char *name;
/* full name for this scheduler
*/
char *opt_name;
/* option name for this scheduler
*/
unsigned int sched_id; /* ID for this scheduler
*/
void
(*init)
(void);
int
(*init_domain)
(struct domain *);
void
(*destroy_domain) (struct domain *);
int
(*init_vcpu)
(struct vcpu *);
void
(*destroy_vcpu)
(struct vcpu *);
void
(*sleep)
(struct vcpu *);
void
(*wake)
(struct vcpu *);
struct task_slice (*do_schedule) (s_time_t);
int
(*pick_cpu)
(struct vcpu *);
int
(*adjust)
(struct domain *, struct xen_domctl_scheduler_op *);
void
(*dump_settings) (void);
INTEL CONFIDENTIAL
void
(*dump_cpu_state) (int);
};
Xen Para-Virtual
functionality
INTEL CONFIDENTIAL
Paravirtualized architecture
We’ll review the PV mechanisms that support this architecture:
Kernel Initialization
Hypercalls creation
Event channels
XenStore (some kind of registry)
Memory transfers between VMs
Split device drivers
Paravirtual Guest
Domain 0
Real
device
driver
Backen
d device
driver
Shared Ring
Buffers
Hypervisor
Block devices
INTEL CONFIDENTIAL
Hardware
Fronten
d device
driver
Initial information for booting a PV OS
•
First things the OS needs to know when boots:
– Available RAM, connected peripherals, access to the machine clock.
•
An OS running on a PV Xen environment does not have access to real
firmware
– The information required is provided by the SHARED INFO PAGES.
•
The “domain builder” is in charge of mapping the shared info pages in the
guest’s address space prior its boot.
– Example: launching dom0 in a i386 architecture:
• Refer to function construct_dom0 in xen/arch/x86/domain_build.c
•
The shared info pages does not completely replace a BIOS
– The console device is available via the start info page for debugging purposes;
debugging output from the kernel should be available as early as possible.
– Other devices must be found using the XenStore
INTEL CONFIDENTIAL
The start info page
•
The start info page is loaded in the guest’s address space at boot time. The
way this page is transferred is architecture-dependent; x86 uses the ESI
register.
•
The content of this page is defined by the C structure start_info which is
declared in xen/include/public/xen.h
•
A portion of the fields in the start info page are always available for the guest
domain and are updated every time the virtual machine is resumed because
some of them contain machine addresses (subject to change
INTEL CONFIDENTIAL
start_info structure overview
struct start_info {
/* THE FOLLOWING ARE FILLED IN BOTH ON INITIAL BOOT AND ON RESUME.
*/
char magic[32];
/* "xen-<version>-<platform>".
*/
unsigned long nr_pages;
/* Total pages allocated to this domain. */
unsigned long shared_info; /* MACHINE address of shared info struct. */
uint32_t flags;
/* SIF_xxx flags.
*/
xen_pfn_t store_mfn;
/* MACHINE page number of shared page.
*/
uint32_t store_evtchn;
/* Event channel for store communication. */
union {
struct {
xen_pfn_t mfn;
/* MACHINE page number of console page.
*/
uint32_t evtchn;
/* Event channel for console page.
*/
} domU;
struct {
uint32_t info_off; /* Offset of console_info struct.
*/
uint32_t info_size; /* Size of console_info struct from start.*/
} dom0;
} console;
/* THE FOLLOWING ARE ONLY FILLED IN ON INITIAL BOOT (NOT RESUME).
*/
unsigned long pt_base;
/* VIRTUAL address of page directory.
*/
unsigned long nr_pt_frames; /* Number of bootstrap p.t. frames.
*/
unsigned long mfn_list;
/* VIRTUAL address of page-frame list.
*/
unsigned long mod_start;
/* VIRTUAL address of pre-loaded module. */
unsigned long mod_len;
/* Size (bytes) of pre-loaded module.
*/
int8_t cmd_line[MAX_GUEST_CMDLINE];
}; typedef struct start_info start_info_t;
INTEL CONFIDENTIAL
start_info fields
char magic[32]; /*"xen-<version>-platform>"*/
•
The magic number is the first thing the guest domain must check from its start
info page.
– If the magic string does not start with “xen-” something is seriously wrong and the
best thing to do is abort.
– Also, minor and major versions must be checked in order to determine if the guest
kernel had been tested in this Xen version.
unsigned long nr_pages; /*Total pages allocated to this domain.*/
•
The amount of available RAM is determined by this field. It contains the
number of memory pages available to the domain.
INTEL CONFIDENTIAL
start_info fields (2)
unsigned long shared_info; /*MACHINE address of shared info struct.*/
•
Contains the address of the machine page where the shared info structure is.
The guest kernel should map it to retrieve useful information for its initialization
process.
uint32_t flags;
•
/* SIF_xxx flags.*/
Contains any optional settings for this domain. (defined in xen.h)
– SIF_PRIVILEGED, SIF_INITDOMAIN
xen_pfn_t store_mfn;
•
/* MACHINE page number of shared page.*/
Machine address of the shared memory page used for communication with the
XenStore.
uint32_t store_evtchn; /* Event channel for store communication.*/
•
Event channel used for notifications.
INTEL CONFIDENTIAL
start_info fields (3)
union {
struct {
xen_pfn_t mfn; /* MACHINE page number of console page.*/
uint32_t evtchn; /* Event channel for console page.*/
}domU;
struct {
uint32_t info_off; /*Offset of console_info struct. */
uint32_t info_size; /*Size of console_info struct from start.*/
}dom0;
}console;
•
•
Domain 0 guests uses the dom0 part, which contains the memory offset and
size of the structure used to define the Xen console.
For unprivileged domains the domU part of the union is used .The fields in this
represent a shared memory page and event channel used to identify the
console device.
INTEL CONFIDENTIAL
The shared Info Page
•
•
•
The shared info contains information that is dynamically updated as the system
runs.
It is explicitly mapped by the guest.
The content of this page is defined by the C structure shared_info which is
declared in xen/include/public/xen.h
vcpu_info_t
arch_vcpu_t
shard_info_t
evtchn_upcall_pending
evtchn_upcall_mask
evtchn_pending_sel
cr2
pad
arch
vcpu_info[]
time
arch_time_info_t
evtchn_pending
version
evtchn_mask
pad0
wc_version
tsc_timestamp
wc_sec
system_time
arch_shared_info_t
tsc_to_system_mul
wc_nsec
arch
INTEL CONFIDENTIAL
max_pfn
tsc_shift
pfn_to_mfn_frame_list_list
pad1
shared_info fields
struct vcpu_info_t vcpu_info[MAX_VIRT_CPUS]
•
This array contains one entry per virtual CPU assigned to the domain. Each array
element is a vcpu_info_t structure containing CPU specific information:
–
–
–
Each virtual CPU has 3 flags relating to virtual interrupts (asynchronously delivered events).
• uint8_t evtchn_upcall_pending: it is used by Xen to notify the running system that
there are upcalls currently waiting for delivery on this virtual CPU.
• uint8_t evtchn_upcall_mask: This is the mask for the previous field. This mask
prevents any upcalls being delivered to the running virtual CPU.
• unsigned long evtchn_pending_sel: Indicates which event is waiting. The event
bitmap is an array of machine words, and this value indicates which word in the
evtchn_pending field of the parent structure indicates the raised event.
arch
• Architecture-specific information.
– On x86, this include the virtual CR2 register, that contains the linear address of the
last page fault, but can only be read from ring 0. This is automatically copied by the
hypervisor’s page fault handler before raising the event with the guest domain.
time
• This field, along with a number of fields sharing the wc_ (wall clock) prefix, is used to
implement time keeping in paravirtualized Xen guests.
INTEL CONFIDENTIAL
shared_info fields (2)
unsigned long evtchn_pending[sizeof(unsigned long) * 8];
•
This is a bitmap that indicates which event channels have events waiting. (256
and 512 event channels on a 32 and 64-bit systems respectively)
– Bits are set by the hypervisor and cleared by the guest.
unsigned long evtchn_mask[sizeof(unsigned long) * 8];
•
This bitmap determines whether an event on a particular channel should be
delivered asynchronously
– Every time an event is generated, the corresponding bit in evtchn_pending is set
to 1. If the corresponding bit in evtchn_mask is set to 0, the hypervisor issues an
upcall and delivers the event asynchronously. This allows the guest kernel to switch
between interrupt-driven and polling mechanisms on a per-channel basis.
struct arch_shared_info arch;
•
On x86 arch the arch_shared_info structure contains two fields; max_pfn and
pfn_to_mfn_frame_list_list related to pseudo-physical to machine memory
mapping.
INTEL CONFIDENTIAL
An exercise:
The simplest Xen kernel
INTEL CONFIDENTIAL
The simplest Xen kernel
•
Bootstrap
–
–
–
•
Kernel.c
–
–
–
•
Each Xen guest kernel must start with a section __xen_guest for the bootloader, with key-value pairs
•
GUEST_OS: name of the running kernel
•
XEN_VER: specifies the Xen version for which the guest was implemented
•
VIRT_BASE: guest’s address space this allocation is mapped (0 for kernels)
•
ELF_PADDR_OFFSET: value subtracted from addresses in ELF headers (0 for kernels)
•
HYPERCALL_PAGE: specifies the page number where the hypercall trampolines will be set
•
LOADER: special boot loaders (currently only generic is available)
After mapping everything into memory at the right places, Xen passes control to the guest kernel
•
A trampoline is defined _start
– Clears the direction flag, sets up the stack and calls the kernel start passing the start info page
address in the ESI register as a parameter
A guest kernel is expected to setup handlers to receive events at boot time, otherwise the kernel is not able to
respond to the outside world (it is ignored in the book’s example)
The start_kernel routine takes the start info page as the parameter (passed through the ESI)
The stack is reserved in this file, although it was referenced in bootstrap as well for creating the trampoline routine
If the hypervisor was compiled with debugging, then the HYPERVISOR_console_io will send the string to the
console (otherwise the hypercall fails)
Debug.h
–
–
The hypercall takes three arguments: the command (write), the length of the string and the string pointer
The hypercall # is 18 (xen/include/public/xen.h)
INTEL CONFIDENTIAL
Hypercalls
INTEL CONFIDENTIAL
Executing Privileged instructions from
apps
Because guest kernels don’t run at ring 0 they’re not allowed to execute privileged
instructions, a mechanism is needed to execute them in the right ring, supose exit(0):
push dword 0
mov eax, 1
push eac
int 80h
Paravirtualized
Native
Ring 0
Hypervisor
Kernel
The Hypervisor
has the
interrupts table
Ring 1
Kernel
Ring 2
Ring 3
Application
INTEL CONFIDENTIAL
System Call
Hypercall
Direct System Call (Xen
specific)
Application
Replacing Privileged instructions with
Hypercalls
Unmodified guests use privileged instructions which require transition to ring 0, causing performance
penalty if resolved by the hypervisor
Paravirtual guests replace their privilege instructions by hypercalls
Xen uses 2 mechanisms for hypercalls:
1. An int 82h is used as the channel similar to system calls (deprecated after Xen 3.0)
2. Issued indirectly using the hypercall page provided when the guest is started
For the second mechanism, macros are provided to write hypercalls
#define _hypercall2(type, name, a1, a2)
({
long __res, __ign1, __ign2;
asm volatile (
"call hypercall_page + ("STR(__HYPERVISOR_##name)" * 32)"\
: "=a" (__res), "=b" (__ign1), "=c" (__ign2)
\
: "1" ((long)(a1)), "2" ((long)(a2))
\
: "memory" );
(type)__res;
})
\
\
\
\
\
\
A PV Xen guest uses the HYPERVISOR_sched_op function with SCHEDOP_yield argument instead of
using the privileged instruction HLT, in order to relinquish CPU time to guests with running tasks
static inline int HYPERVISOR_sched_op(int cmd, void *arg)
{
return _hypercall2(int, sched_op, cmd, arg);
}
extras/mini-os/include/x86/x86_32/hypercall-x86_32.h, implemented at xen/common/schedule.c
INTEL CONFIDENTIAL
Event Channels
INTEL CONFIDENTIAL
Event Channels
Event channels are the basic primitive provided by Xen for event notifications, equivalent of a
hardware interrupt valid for paravirtualized OSs
Events are one bit of information signaled by transitioning from 0 to 1
• Physical IRQs: mapped from real IRQs used to communicate with hardware devices
• Virtual IRQs: similar to PIRQs, but related to virtual devices such as the timer, debug
console
• Interdomain events: bidirectional interrupts that notify domains about certain event
• Intradomain events: special case of interdomain events
Domain 0
Domain
Management
and Control
Domain U
Paravirtual Guest
Event
Channel
driver
Hypervisor - VMM
Hardware
INTEL CONFIDENTIAL
Event Channel Interface
Guests configure the Event Channel and send interrupts by issuing a specific hypercall:
HYPERVISOR_event_channel_op (...)
Guests are notified about pending events through callbacks installed during initialization,
these events can be masked dynamically
HYPERVISOR_set_callbacks(…)
Domain 0
Domain
Management
and Control
Domain U
Paravirtual Guest
Event
Channel
driver
Callback
HYPERVISOR_event_channel_op
Hypervisor - VMM
Hardware
INTEL CONFIDENTIAL
HYPERVISOR_event_channel_op – 1/2
HYPERVISOR_event_channel_op(int cmd, void *arg)
// defined at xen-3.1.0-src\linux-2.6-xen-sparse\include\asm-
i386\mach-xen\asm\hypercall.h
•
EVTCHNOP_alloc_unbound: Allocate a new event channel port, ready to be connected to by a
remote domain
–
–
•
EVTCHNOP_bind_interdomain: Bind an event channel for interdomain communications
–
–
–
–
•
Caller domain must have a free port to bind.
VIRQ must be valid.
VCPU must exist.
VIRQ must not currently be bound to an event channel
EVTCHNOP_bind_ipi: Allocate and bind a port for notifying other virtual CPUs.
–
–
•
Caller domain must have a free port to bind.
Remote domain must exist.
Remote port must be allocated and currently unbound.
Remote port must be expecting the caller domain as the remote.
EVTCHNOP_bind_virq: Allocate a port and bind a VIRQ to it
–
–
–
–
•
Specified domain must exist
A free port must exist in that domain
Caller domain must have a free port to bind.
VCPU must exist.
EVTCHNOP_bind_pirq: Allocate and bind a port to a real IRQ.
–
–
–
Caller domain must have a free port to bind.
PIRQ must be within the valid range.
Another binding for this PIRQ must not exist for this domain.
INTEL CONFIDENTIAL
HYPERVISOR_event_channel_op – 2/2
HYPERVISOR_event_channel_op(int cmd, void *arg)
/* defined at xen-3.1.0-src\linux-2.6-xen-sparse\include\asm-
i386\mach-xen\asm\hypercall.h */
•
EVTCHNOP_close: Close an event channel (no more events will be received).
–
•
EVTCHNOP_send: Send a notification on an event channel attached to a port.
–
•
Port must be valid (currently allocated).
Port must be valid.
EVTCHNOP_status: Query the status of a port; what kind of port, whether it is bound, what remote
domain is expected, what PIRQ or VIRQ it is bound to, what VCPU will be notified, etc.
–
–
Unprivileged domains may only query the state of their own ports.
Privileged domains may query any port.
INTEL CONFIDENTIAL
Issuing event channel hypercalls
Structures defined at xen-3.1.0-src\xen\include\public\event_channel.h
Hypervisor handlers defined at xen-3.1.0-src\xen\common\event_channel.c
•
Allocating an unbound event channel
evtchn_alloc_unbound_t op;
op.dom = DOMID_SELF;
op.remote_dom = remote_domain; /* an integer representing the domain */
if(HYPERVISOR_event_channel_op(EVTCHOP_alloc_unbound, &op) != 0)
{
/* Error */
}
•
Binding an event channel for interdomain communication
evtchn_bind_interdomain_t op;
op.remote_dom = remote_domain;
op.remote_port = remote_port;
if(HYPERVISOR_event_channel_op(EVTCHOP_bind_interdomain, &op) != 0)
{
/* Error */
}
INTEL CONFIDENTIAL
HYPERVISOR_set_callbacks
Hypercall to configure the notification handlers
HYPERVISOR_set_callbacks(
unsigned long event_selector, unsigned long event_address,
unsigned long failsafe_selector, unsigned long failsafe_address)
/* defined at xen-3.1.0-src\linux-2.6-xen-sparse\include\asm-i386\mach-xen\asm\hypercall.h */
•
•
event_selector + event_address: make the callback address for notifications
failsafe_selector + failsafe_address: make the callback if anything goes wrong with the
event
Notifications can be prevented at a VCPU level or at an event level because they’re
contained in the shared info page:
struct shared_info {…
struct vcpu_info vcpu_info[MAX_VIRT_CPUS] {…
uint8_t evtchn_upcall_mask;…};
unsigned long evtchn_mask[sizeof(unsigned long) * 8];
…};
INTEL CONFIDENTIAL
Setting the notifications handler
Handler and masks configuration
/* Locations in the bootstrapping code */
extern volatile shared_info_t shared_info;
void hypervisor_callback(void);
void failsafe_callback(void);
static evtchn_handler_t handlers[NUM_CHANNELS];
void EVT_IGN(evtchn_port_t port, struct pt_regs * regs) {};
/* Initialise the event handlers */
void init_events(void)
{
/* Set the event delivery callbacks */
HYPERVISOR_set_callbacks(
FLAT_KERNEL_CS, (unsigned long)hypervisor_callback,
FLAT_KERNEL_CS, (unsigned long)failsafe_callback);
/* Set all handlers to ignore, and mask them */
for(unsigned int i=0 ; i<NUM_CHANNELS ; i++)
{
handlers[i] = EVT_IGN;
SET_BIT(i,shared_info.evtchn_mask[0]);
}
/* Allow upcalls. */
shared_info.vcpu_info[0].evtchn_upcall_mask = 0;
}
INTEL CONFIDENTIAL
Implementing the callback function
/* Dispatch events to the correct handlers */
void do_hypervisor_callback(struct pt_regs *regs)
{
unsigned int pending_selector, next_event_offset;
vcpu_info_t *vcpu = &shared_info.vcpu_info[0];
/* Make sure we don't lose the edge on new events... */
vcpu->evtchn_upcall_pending = 0;
/* Set the pending selector to 0 and get the old value atomically */
pending_selector = xchg(&vcpu->evtchn_pending_sel, 0);
while(pending_selector != 0)
{
/* Get the first bit of the selector and clear it */
next_event_offset = first_bit(pending_selector);
pending_selector &= ~(1 << next_event_offset);
unsigned int event;
Maps a bit with an
index in the
callback matrix
/* While there are events pending on unmasked channels */
while(( event = (shared_info.evtchn_pending[pending_selector] & ~shared_info.evtchn_mask[pending_selector])) != 0)
{
/* Find the first waiting event */
unsigned int event_offset = first_bit(event);
/* Combine the two offsets to get the port */
evtchn_port_t port = (pending_selector << 5) + event_offset; /* 5 -> 32 bits */
/* Handle the event */
handlers[port](port, regs);
/* Clear the pending flag */
CLEAR_BIT(shared_info.evtchn_pending[0], event_offset);
}
}
}
INTEL CONFIDENTIAL
XenStore
INTEL CONFIDENTIAL
Xen Store
XenStore is a hierarchical namespace (similar to sysfs or Open Firmware) which is shared
between domains
The interdomain communication primitives exposed by Xen are very low-level (virtual IRQ
and shared memory)
XenStore is implemented on top of these primitives and provides some higher level
operations (read a key, write a key, enumerate a directory, notify when a key changes
value)
General Format
There are three main paths in XenStore:
•
/vm - stores configuration information about domain
•
/local/domain - stores information about the domain on the local node (domid, etc.)
•
/tool - stores information for the various tools
Detailed information at http://wiki.xensource.com/xenwiki/XenStoreReference
INTEL CONFIDENTIAL
Ring buffers for split driver model
•
•
•
•
The ring buffer is a fairly standard lockless data structure for producer-consumer
communications
Xen uses free-running counters
Each ring contains two kinds of data, a request and a response, updated by the two
halves of the driver
Xen only allows responses to be written in a way that overwrites requests
Domain 0 Back End
Domain U Front End
Request Notification Events
Read Request
Write Request
Write Response
DomU writes Request 1
DomU reads Response 1
INTEL CONFIDENTIAL
Read Response
DomU writes Request 2
Response Notification Events
Dom0 writes Response 2
Dom0 writes Response 1
DomU reads Response 2
Xen Split Device Driver Model (for PV
guests)
Xen delegates hardware support typically to Domain 0, and device drivers typically consist of
four main components:
•
The real driver
•
The back end split driver
•
A shared ring buffer (shared memory pages and events notification)
•
The front end split driver
Paravirtual Guest
Domain 0
Real
device
driver
Backen
d device
driver
Shared Ring
Buffers
Hypervisor
Block devices
INTEL CONFIDENTIAL
Hardware
Fronten
d device
driver
Xen HVM functionality
INTEL CONFIDENTIAL
Xen HVM
Hardware Virtual Machines allow unmodified Operating Systems to run on Virtual Environments
This approach brings 2 kinds of problems:
For the unmodified OS, the VM must appear as a real PC
Hardware access
-
To keep isolation device emulation must be provided from Domain 0
Provide direct assignment from a VM to a specific HW
Domain 0
Domain U - HVM
Qemu-dm
Xen virtual firmware
Every HVM has a qemu-dm counterpart
Virtual BIOS to provide standard start-up
Handles networking and disk access from HVM Composed of 3 payloads
Based in QEMU project
Vmxassist: real mode emulator for VMX
VGA BIOS
ROM BIOS
INTEL CONFIDENTIAL
Xen QEMU-dm / Virtual firmware
interaction
Domain 0
Domain U - HVM
Qemu-dm
Xen virtual firmware
Xen Virtual firmware works as the front end driver in the split driver model
1.
2.
3.
4.
5.
Guest issues a BIOS interrupt requesting data to be loaded from disk
The virtual BIOS translates the call into a request to the block device
The vBIOS interrupt is caught by QEMU-dm
QEMU-dm emulates the hardware and translates that to the real hardware in Domain 0
The inverse process happens for the response
INTEL CONFIDENTIAL
HVM domain creation
Once the domain builder is specified as “hvm”:
1. Allocates and verifies memory for domain
2. Loads the hvmloader as a kernel (setup_guest at xc_hvm_build.c)
3. Initializes hypercalls table and verifies that Xen is active
4. Copies BIOS image to 0x000F0000 created from Bochs (tools/firmware/rombios)
5. Discovers and sets up PCI devices
6. Loads a VGA BIOS
7. For Intel platforms, loads real-mode emulator for VMX (tools/firmware/vmxassist)
INTEL CONFIDENTIAL
HVM support in Xen
Support for hardware virtualization is done through an abstract interface defined at xen/include/asm-x86/hvm
struct hvm_function_table {
char *name;
void (*disable)(void);
int (*vcpu_initialise)(struct vcpu *v);
void (*vcpu_destroy)(struct vcpu *v);
void (*store_cpu_guest_regs)(struct vcpu *v, struct cpu_user_regs *r, unsigned long *crs);
void (*load_cpu_guest_regs)(struct vcpu *v, struct cpu_user_regs *r);
void (*save_cpu_ctxt)(struct vcpu *v, struct hvm_hw_cpu *ctxt);
int (*load_cpu_ctxt)(struct vcpu *v, struct hvm_hw_cpu *ctxt);
int (*paging_enabled)(struct vcpu *v);
int (*long_mode_enabled)(struct vcpu *v);
int (*pae_enabled)(struct vcpu *v);
int (*interrupts_enabled)(struct vcpu *v);
int (*guest_x86_mode)(struct vcpu *v);
unsigned long (*get_guest_ctrl_reg)(struct vcpu *v, unsigned int num);
unsigned long (*get_segment_base)(struct vcpu *v, enum x86_segment seg);
void (*get_segment_register)(struct vcpu *v, enum x86_segment seg, struct segment_register *reg);
void (*update_host_cr3)(struct vcpu *v);
void (*update_guest_cr3)(struct vcpu *v);
void (*update_vtpr)(struct vcpu *v, unsigned long value);
void (*stts)(struct vcpu *v);
void (*set_tsc_offset)(struct vcpu *v, u64 offset);
void (*inject_exception)(unsigned int trapnr, int errcode, unsigned long cr2);
void (*init_ap_context)(struct vcpu_guest_context *ctxt, int vcpuid, int trampoline_vector);
void (*init_hypercall_page)(struct domain *d, void *hypercall_page);
int (*event_injection_faulted)(struct vcpu *v);
};
INTEL CONFIDENTIAL
Intel VT support in Xen
The hvm_function_table is initialized at xen/arch/x86/hvm/vmx/vmx.c
The following routines store and load completely save the state of a CPU through the VMCS
.store_cpu_guest_regs = vmx_store_cpu_guest_regs
.load_cpu_guest_regs = vmx_load_cpu_guest_regs
This status copy is performed in a single instruction
struct vmcs_struct {
u32 vmcs_revision_id;
unsigned char data [0]; /* vmcs size is read from MSR */
};
INTEL CONFIDENTIAL
KVM overview
INTEL CONFIDENTIAL
What is KVM?
• It’s a VMM built within the Linux kernel
– The name stands for Kernel Virtual Machines
– It is included in mainline Linux, as of 2.6.20
• It offers full-virtualization
– Para-virtualization support is in alpha state
• It works *only* in platforms with hardware-assisted virtualization
– Currently only Intel-VT and AMD-V
– Recently also s390, PowerPC and IA64
• Decision taken to achieve a simple design
–
–
–
–
No need to deal with ring aliasing problem,
Nor excessive faulting avoidance
Nor guest memory management complexity
Etc
INTEL CONFIDENTIAL
Why KVM?
• Today’s hardware is becoming increasingly complex
–
–
–
–
Multiple HW threads on a core
Multiple cores on a socket
Multiple sockets on a system
NUMA memory models (on-chip memory controllers)
• Scheduling and memory management is becoming harder accordingly
• Great effort is required to program all this complexity in hypervisors
– But an operating system kernel already handles this complexity
– So why no reuse it?
• KVM makes use of all the fine-tuning work that has gone (and is going)
into the Linux kernel, applying it to a virtualized environment
• Minimal footprint
– Less than 10K lines of kernel code
– Implemented as a Linux’s module
INTEL CONFIDENTIAL
How it works?
• A normal Linux process has two modes of execution: kernel and user
– KVM adds a third mode: guest mode
• A virtual machine in KVM will be “seen” as a normal Linux process
– A portion of code will run in user mode: performs I/O on behalf of the guest
– A portion of code will run in guest mode: performs non-I/O guest code
guest
mode
With its
own 4
rings
INTEL CONFIDENTIAL
Key features
•
Simpler design: Kernel+Userspace (vs. Hypervisor+Kernel+Userspace)
– Avoids many context switches
– Code reuse (today and tomorrow)
– Easy management of VMs (standard process tools)
•
Supports Qcow2 and Vmdk disk image formats
–
–
–
•
“Growable” formats (copy-on-write)
Saved state of a VM with X Mb of RAM takes less than X Mb of file space
• KVM skips RAM sectors mapped by itself
• KVM uses the on-the-fly compression capability of Qcow2 and VMDK formats
• I.e. an save state of a 384Mb’s Windows VM occupies ~40Mb
Discard-on-write capability (read’s made from base image A, write’s goes to new image B)
• B will contain the differences from A performed by the VM
• Later, B diff’s can be merged into A
Advanced guest memory management
–
–
–
Increased VM density with KSM (under development)[3]
• KSM is a kernel module to save memory by searching and merging identical pages inside one
or more memory areas
Balloon driver as in Xen
Guest’s page swapping allowed
INTEL CONFIDENTIAL
Future trends
•
Para-virtualization support (Windows & Linux)
–
•
virtio devices already included in Linux’s mainline as of 2.6.25
Storage[4]
–
–
–
Many similar guests cause a lot of duplicate storage
Current solution: baseline + delta images
• Delta degrades overtime (needs planning)
• Disk-in-file is overheady
Future:
• Block-level deduplication
– Filesystem or block device looks for identical blocks ... and consolidates them
– Btrfs being analyzed right now (has snapshots & reverse mappings)
• Hostfs + file-based deduplication
– No more virtual block device. Guest filesystem is a host directory
– Host can carry out file dedup in the background
– Requires changes in guest
• Para-virtualized file systems (9P from IBM Research)[2]
– Easy way to maintain consistency between two guests sharing a block device R/W
– Provide a direct file system proxy mechanism built on top of the native host<->guest I/O
transport, avoiding unnecessary network stack overhead
INTEL CONFIDENTIAL
Future trends (2)
•
Containers & Isolation (reduce the impact of one guest on others)
–
–
•
Device passthrough methods
–
–
•
Several competing options
• 1:1 mapping with Intel VT-d
• Virtualization-capable devices with PCI SIG Single Root IOV
• PVDMA
• Userspace IRQ delivery
Still to see which will become mainline
VMs-AS-FILES
–
–
•
Memory containers
• Account each page to its container
• Allows preferentially swapping some guests
I/O accounting (since I/O affects other guests)
• Each I/O in flight is correctly accounted to initiating task
• Important for I/O scheduling
Cross-hypervisor virtualization containers to allow for transportability of VMs
OVF: Open Virtual Appliance Format[5]
Cross platform guest support (QuickTransit technology[6])
–
I.e. a Solaris for Sparc running in an Intel platform
INTEL CONFIDENTIAL
VMware overview
INTEL CONFIDENTIAL
VMware
In 1998, VMware created a solution to virtualize the x86 platform, creating the market for x86 virtualization
The solution was a combination of binary translation and direct execution on the processor
Nonvirtualizable instructions are replaced with new
sequences of instructions
User level code is directly executed on the processor
Each VMM provides each VM with all the services of the
physical system, including a virtual BIOS, virtual
devices and virtualized memory management
INTEL CONFIDENTIAL
VMware ESX architecture
Datacenter-class virtualization platform used by many enterprise customers for server consolidation
Runs directly on a physical server having direct access to the physical hardware of the server
•
•
•
•
•
Virtualization layer (VMM/VMKernel): implements the idealized hardware environment and
virtualizes the physical hardware devices
Resource Manager: partitions and controls the physical resources of the underlying machine
Hardware interface components: enable hardware-specific service delivery
Service Console: boots the system, initiates execution of the virtualization layer and resource
manager, and relinquishes control to those layers
Add
–
Virtual Center / Lab manager
INTEL CONFIDENTIAL
VMware default deployment
Primary method of
interaction with virtual
infrastructure (console
and GUI)
Authorizes
VirtualCenter Servers and ESX
Server hosts appropriately for
the licensing
agreement
Virtualization layer that
abstracts the
processor, memory, storage,
and networking resources of
the physical host into
multiple virtual machines
Organizes all the
configuration data for the
virtual infrastructure
environment
VI Client from the
VirtualCenter Server
or ESX Server hosts
Centrally
manages the VMware
ESX Server hosts
INTEL CONFIDENTIAL
VMware for free
VMware provides freeware Server and Workstation virtualization solutions
• VMware Server:
–
–
–
–
•
Is a free desktop application that lets you run virtual machines on your Windows or Linux PC
Lets you use host machine devices, such as CD and DVD drives, from the virtual machine
Datasheet or FAQ page is available
Different Virtual Appliances are provided for free
VMware Player:
–
Similar to VMware Server but limited to run pre-built virtual appliances
INTEL CONFIDENTIAL
OpenVZ overview
Operating System
virtualization
INTEL CONFIDENTIAL
OpenVZ
•
•
•
•
•
OpenVZ is an open source server virtualization solution that creates multiple isolated
Virtual Private Servers (VPSs) or Virtual Environments (VEs) on a single physical server
VPS perform and execute exactly like a stand-alone server for its users and applications
as it can be rebooted independently
All VPSs have their own set of processes and can run different Linux distributions, but all
VPSs operate under the same kernel
OpenVZ is the basis of Parallels/Virtuozzo Containers
Distinctive features:
–
–
–
–
•
•
Operating System Virtualization
Network Virtualization
Resource Management
Templates
Installation: http://wiki.openvz.org/Quick_installation
User documentation: http://download.openvz.org/doc/OpenVZ-Users-Guide.pdf
INTEL CONFIDENTIAL
OpenVZ Kernel
The OpenVZ kernel is a modified Linux kernel which adds the following functionality:
•
Virtualization and isolation: enables many virtual environments within a single kernel
•
Resource management: subsystem limits (and in some cases guarantees) resources
such as CPU, RAM, and disk space on a per-VE basis
•
Live Migration/Checkpointing: a process of “freezing” a VE, saving its complete state
to a disk file, with the ability to “unfreeze” that state later
INTEL CONFIDENTIAL
OpenVZ Kernel Virtualization and Isolation
Each Virtual Environment has its own set of virtualized/isolated resources, such as:
•
Files
–
•
Users and groups
–
•
Virtual network device, which allows the VE to have its own IP addresses, as well as a set of netfilter (iptables)
and routing rules.
Devices
–
•
A VE sees only its own set of processes, starting from init. PIDs are virtualized, so that the init PID is 1 as it
should be.
Network
–
•
Each VE has its own root user, as well as other users and groups.
Process tree
–
•
System libraries, applications, virtualized /proc and /sys, virtualized locks, etc.
Devices are virtualized. In addition, any VE can be granted exclusive access to real devices like network
interfaces, serial ports, disk partitions, etc.
IPC objects
–
Shared memory, semaphores, and messages.
INTEL CONFIDENTIAL
OVZ Resource Management
Resource management subsystem consists of three components:
•
Two-level disk quota:
–
–
•
“Fair” CPU 2 level scheduler:
–
–
•
1st level: Server administrator can set up per-VE disk quotas in terms of disk space and number of inodes
2nd level: VE administrator (VE root) uses standard UNIX quota tools to set up per-user and per-group disk
quotas.
1st level: decides which VE to give the time slice to, taking into account the VE’s CPU priority and limit settings
2nd level: standard Linux scheduler decides which process in the VE to give the time slice to, using standard
process priorities.
User Beancounters
–
–
–
This is a set of per-VE counters, limits, and guarantees
Set of about 20 parameters which are carefully chosen to cover all the aspects of VE operation, so no single VE
can abuse any resource which is limited for the whole computer and thus cause harm to other VEs
The resources accounted and controlled are mainly memory and various in-kernel objects such as IPC shared
memory segments, network buffers etc.
INTEL CONFIDENTIAL
OpenVZ Checkpointing and live migration
Allows the “live” migration of a VE to another physical server
A “frozen” VE and its complete state is saved to a disk file, then transferred to another
machine
This VE can then be “unfrozen” (restored) there (the whole process takes a few seconds, and
from the client’s point of view it looks not like a downtime, but rather a delay in
processing, since the established network connections are also migrated)
Live migration
Virtual
Env
Virtual
Env
OpenVZ
OpenVZ
Host
Host
INTEL CONFIDENTIAL
Disk
Checkpoint
Backup
INTEL CONFIDENTIAL
Xen Terminology – 1/2
Basics
guest operating system: An operating system that can run within the Xen environment.
hypervisor: Code running at a higher privilege level than the supervisor code of its guest operating systems.
virtual machine monitor ("vmm"): In this context, the hypervisor.
domain: A running virtual machine within which a guest OS executes.
domain0 ("dom0"): The first domain, automatically started at boot time. Dom0 has permission to control all hardware on the system, and is used to manage the hypervisor and the other
domains.
unprivileged domain ("domU"): A domain with no special hardware access.
Approaches to Virtualization
full virtualization: An approach to virtualization which requires no modifications to the hosted operating system, providing the illusion of a complete system of real hardware devices.
paravirtualization: An approach to virtualization which requires modifications to the operating system in order to run in a virtual machine. Xen uses paravirtualization but preserves binary
compatibility for user space applications.
Address Spaces
MFN (machine frame number): Real host machine address; the addresses the processor understands.
GPFN (guest pseudo-physical frame number): Guests run in an illusory contiguous physical address space, which is probably not contiguous in the machine address space.
GMFN (guest machine frame number): Equivalent to GPFN for an auto-translated guest, and equivalent to MFN for normal paravirtualised guests. It represents what the guest thinks are
MFNs.
PFN (physical frame number): A catch-all for any kind of frame number. "Physical" here can mean guest-physical, machine-physical or guest-machine-physical.
Page Tables
SPT (shadow page table): shadow version of a guest OSes page table. Useful for numerous things, for instance in tracking dirty pages during live migration.
PAE: Intel's Physical Addressing Extensions, which enable x86/32 machines to address up to 64 GB of physical memory.
PSE (page size extension): used as a flag to indicate that a given page is ahuge/super page (2/4 MB instead of 4KB).
x86 Architecture
HVM: Hardware Virtual Machine, which is the full-virtualization mode supported by Xen. This mode requires hardware support, e.g. Intel's Virtualization Technology (VT) and AMD's
Pacifica technology.
VT-x: full-virtualization support on Intel's x86 VT-enabled processors
VT-i: full-virtualization support on Intel's IA-64 VT-enabled processors
Extracted from: http://wiki.xensource.com/xenwiki/XenTerminology
INTEL CONFIDENTIAL
Xen Terminology – 2/2
Networking Infrastructure
backend: one half of a communication end point - interdomain communication is implemented using a frontend and backend device model interacting via event channels.
frontend: the device as presented to the guest; other half of the communication endpoint.
vif: virtual interface; the name of the network backend device connected by an event channel to a network front end on the guest.
vethN: local networking front end on dom0; renamed to ethN by xen network scripts in bridging mode (FIXME)
pethN: real physical device (after renaming)
Migration
Live migration: A technique for moving a running virtual machine to another physical host, without stopping it or the services running on it.
Scheduling
BVT: The Borrowed Virtual Time scheduler is used to give proportional fair shares of the CPU to domains.
SEDF: The Simple Earliest Deadline First scheduler provides weighted CPU sharing in an intuitive way and uses realtime algorithms to ensure time guarantees.
Extracted from: http://wiki.xensource.com/xenwiki/XenTerminology
INTEL CONFIDENTIAL
Intel privileged instructions
Some of the system instructions (called “privileged instructions”) are protected from use by application
programs. The privileged instructions control system functions (such as the loading of system
registers). They can be executed only when the CPL is 0 (most privileged). If one of these instructions
is executed when the CPL is not 0, a general-protection exception (#GP) is generated. The following
system instructions are privileged instructions (16):
•
LGDT — Load GDT register.
•
LLDT — Load LDT register.
•
LTR — Load task register.
•
LIDT — Load IDT register.
•
MOV (control registers) — Load and store control registers.
•
LMSW — Load machine status word.
•
CLTS — Clear task-switched flag in register CR0.
•
MOV (debug registers) — Load and store debug registers.
•
INVD — Invalidate cache, without writeback.
•
WBINVD — Invalidate cache, with writeback.
•
INVLPG —Invalidate TLB entry.
•
HLT— Halt processor.
•
RDMSR — Read Model-Specific Registers.
•
WRMSR —Write Model-Specific Registers.
•
RDPMC — Read Performance-Monitoring Counter.
•
RDTSC — Read Time-Stamp Counter.
INTEL CONFIDENTIAL
QEMU Description http://bellard.org/qemu/
http://bellard.org/qemu/qemu-tech.html
A fast processor emulator using a portable dynamic emulator
2 operating modes (add diagrams for each case):
•
Full system emulation
•
User mode emulation
Generic features:
•
User space only or full system emulation
•
Using dynamic translation to native code for reasonable speed
•
Working on x86 and PowerPC hosts. Being tested on ARM, Sparc32, Alpha and S390
•
Self-modifying code support
•
Precise exceptions support
•
The virtual CPU is a library (libqemu) which can be used in other projects
QEMU full system emulation features:
•
QEMU can either use a full software MMU for maximum portability or use the host system call
mmap() to simulate the target MMU
INTEL CONFIDENTIAL
QEMU x86 emulation
QEMU x86 target features:
•
Support for 16 bit and 32 bit addressing with segmentation. LDT/GDT and IDT are emulated.
VM86 mode is also supported to run DOSEMU
•
Support of host page sizes bigger than 4KB in user mode emulation
•
QEMU can emulate itself on x86
Current QEMU limitations:
•
No SSE/MMX support
•
No x86-64 support
•
IPC syscalls are missing
•
The x86 segment limits and access rights are not tested at every memory access
•
On non x86 host CPUs, doubles are used instead of the non standard 10 byte long doubles of
x86 for floating point emulation to get maximum performances.
INTEL CONFIDENTIAL
References
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Intel® 64 and IA-32 Architectures - Software Developer’s Manual
http://wiki.xensource.com/xenwiki/XenArchitecture?action=AttachFile&do=get&target=Xen+Architectur
e_Q1+2008.pdf
http://wiki.xensource.com/xenwiki/XenArchitecture
http://www.xen.org/files/xensummit_4/Liguori_XenSummit_Spring_2007.pdf
http://wiki.xensource.com/xenwiki/XenTerminology
http://www.xen.org/xen/faqs.html
http://www.vmware.com/pdf/esx2_performance_implications.pdf
http://www.vmware.com/files/pdf/VMware_paravirtualization.pdf
http://download.openvz.org/doc/OpenVZ-Users-Guide.pdf
http://download.openvz.org/doc/openvz-intro.pdf
KVM project @ Sourceforge.net
Paravirtualized file systems, KVM Forum 2008.
Increasing Virtual Machine density with KSM, KVM Forum 2008.
Beyond kvm.ko, KVM Forum 2008.
Open-OVF: an OSS project around the Open Virtual Appliance format, KVM Forum 2008.
Cross platform guest support, KVM Forum 2008.
INTEL CONFIDENTIAL