-KVM-specific MSRs.
-Glauber Costa <glommer@redhat.com>, Red Hat Inc, 2010
-=====================================================
+.. SPDX-License-Identifier: GPL-2.0
+
+=================
+KVM-specific MSRs
+=================
+
+:Author: Glauber Costa <glommer@redhat.com>, Red Hat Inc, 2010
KVM makes use of some custom MSRs to service some requests.
but they are deprecated and their use is discouraged.
Custom MSR list
---------
+---------------
The current supported Custom MSR list is:
-MSR_KVM_WALL_CLOCK_NEW: 0x4b564d00
+MSR_KVM_WALL_CLOCK_NEW:
+ 0x4b564d00
- data: 4-byte alignment physical address of a memory area which must be
+data:
+ 4-byte alignment physical address of a memory area which must be
in guest RAM. This memory is expected to hold a copy of the following
- structure:
+ structure::
- struct pvclock_wall_clock {
+ struct pvclock_wall_clock {
u32 version;
u32 sec;
u32 nsec;
- } __attribute__((__packed__));
+ } __attribute__((__packed__));
whose data will be filled in by the hypervisor. The hypervisor is only
guaranteed to update this data at the moment of MSR write.
Users that want to reliably query this information more than once have
to write more than once to this MSR. Fields have the following meanings:
- version: guest has to check version before and after grabbing
+ version:
+ guest has to check version before and after grabbing
time information and check that they are both equal and even.
An odd version indicates an in-progress update.
- sec: number of seconds for wallclock at time of boot.
+ sec:
+ number of seconds for wallclock at time of boot.
- nsec: number of nanoseconds for wallclock at time of boot.
+ nsec:
+ number of nanoseconds for wallclock at time of boot.
In order to get the current wallclock time, the system_time from
MSR_KVM_SYSTEM_TIME_NEW needs to be added.
Availability of this MSR must be checked via bit 3 in 0x4000001 cpuid
leaf prior to usage.
-MSR_KVM_SYSTEM_TIME_NEW: 0x4b564d01
+MSR_KVM_SYSTEM_TIME_NEW:
+ 0x4b564d01
- data: 4-byte aligned physical address of a memory area which must be in
+data:
+ 4-byte aligned physical address of a memory area which must be in
guest RAM, plus an enable bit in bit 0. This memory is expected to hold
- a copy of the following structure:
+ a copy of the following structure::
- struct pvclock_vcpu_time_info {
+ struct pvclock_vcpu_time_info {
u32 version;
u32 pad0;
u64 tsc_timestamp;
s8 tsc_shift;
u8 flags;
u8 pad[2];
- } __attribute__((__packed__)); /* 32 bytes */
+ } __attribute__((__packed__)); /* 32 bytes */
whose data will be filled in by the hypervisor periodically. Only one
write, or registration, is needed for each VCPU. The interval between
Fields have the following meanings:
- version: guest has to check version before and after grabbing
+ version:
+ guest has to check version before and after grabbing
time information and check that they are both equal and even.
An odd version indicates an in-progress update.
- tsc_timestamp: the tsc value at the current VCPU at the time
+ tsc_timestamp:
+ the tsc value at the current VCPU at the time
of the update of this structure. Guests can subtract this value
from current tsc to derive a notion of elapsed time since the
structure update.
- system_time: a host notion of monotonic time, including sleep
+ system_time:
+ a host notion of monotonic time, including sleep
time at the time this structure was last updated. Unit is
nanoseconds.
- tsc_to_system_mul: multiplier to be used when converting
+ tsc_to_system_mul:
+ multiplier to be used when converting
tsc-related quantity to nanoseconds
- tsc_shift: shift to be used when converting tsc-related
+ tsc_shift:
+ shift to be used when converting tsc-related
quantity to nanoseconds. This shift will ensure that
multiplication with tsc_to_system_mul does not overflow.
A positive value denotes a left shift, a negative value
The conversion from tsc to nanoseconds involves an additional
right shift by 32 bits. With this information, guests can
- derive per-CPU time by doing:
+ derive per-CPU time by doing::
time = (current_tsc - tsc_timestamp)
if (tsc_shift >= 0)
time = (time * tsc_to_system_mul) >> 32
time = time + system_time
- flags: bits in this field indicate extended capabilities
+ flags:
+ bits in this field indicate extended capabilities
coordinated between the guest and the hypervisor. Availability
of specific flags has to be checked in 0x40000001 cpuid leaf.
Current flags are:
- flag bit | cpuid bit | meaning
- -------------------------------------------------------------
- | | time measures taken across
- 0 | 24 | multiple cpus are guaranteed to
- | | be monotonic
- -------------------------------------------------------------
- | | guest vcpu has been paused by
- 1 | N/A | the host
- | | See 4.70 in api.txt
- -------------------------------------------------------------
+
+ +-----------+--------------+----------------------------------+
+ | flag bit | cpuid bit | meaning |
+ +-----------+--------------+----------------------------------+
+ | | | time measures taken across |
+ | 0 | 24 | multiple cpus are guaranteed to |
+ | | | be monotonic |
+ +-----------+--------------+----------------------------------+
+ | | | guest vcpu has been paused by |
+ | 1 | N/A | the host |
+ | | | See 4.70 in api.txt |
+ +-----------+--------------+----------------------------------+
Availability of this MSR must be checked via bit 3 in 0x4000001 cpuid
leaf prior to usage.
-MSR_KVM_WALL_CLOCK: 0x11
+MSR_KVM_WALL_CLOCK:
+ 0x11
- data and functioning: same as MSR_KVM_WALL_CLOCK_NEW. Use that instead.
+data and functioning:
+ same as MSR_KVM_WALL_CLOCK_NEW. Use that instead.
This MSR falls outside the reserved KVM range and may be removed in the
future. Its usage is deprecated.
Availability of this MSR must be checked via bit 0 in 0x4000001 cpuid
leaf prior to usage.
-MSR_KVM_SYSTEM_TIME: 0x12
+MSR_KVM_SYSTEM_TIME:
+ 0x12
- data and functioning: same as MSR_KVM_SYSTEM_TIME_NEW. Use that instead.
+data and functioning:
+ same as MSR_KVM_SYSTEM_TIME_NEW. Use that instead.
This MSR falls outside the reserved KVM range and may be removed in the
future. Its usage is deprecated.
Availability of this MSR must be checked via bit 0 in 0x4000001 cpuid
leaf prior to usage.
- The suggested algorithm for detecting kvmclock presence is then:
+ The suggested algorithm for detecting kvmclock presence is then::
if (!kvm_para_available()) /* refer to cpuid.txt */
return NON_PRESENT;
} else
return NON_PRESENT;
-MSR_KVM_ASYNC_PF_EN: 0x4b564d02
- data: Bits 63-6 hold 64-byte aligned physical address of a
+MSR_KVM_ASYNC_PF_EN:
+ 0x4b564d02
+
+data:
+ Bits 63-6 hold 64-byte aligned physical address of a
64 byte memory area which must be in guest RAM and must be
zeroed. Bits 5-3 are reserved and should be zero. Bit 0 is 1
when asynchronous page faults are enabled on the vcpu 0 when
Currently type 2 APF will be always delivered on the same vcpu as
type 1 was, but guest should not rely on that.
-MSR_KVM_STEAL_TIME: 0x4b564d03
+MSR_KVM_STEAL_TIME:
+ 0x4b564d03
- data: 64-byte alignment physical address of a memory area which must be
+data:
+ 64-byte alignment physical address of a memory area which must be
in guest RAM, plus an enable bit in bit 0. This memory is expected to
- hold a copy of the following structure:
+ hold a copy of the following structure::
- struct kvm_steal_time {
+ struct kvm_steal_time {
__u64 steal;
__u32 version;
__u32 flags;
__u8 preempted;
__u8 u8_pad[3];
__u32 pad[11];
- }
+ }
whose data will be filled in by the hypervisor periodically. Only one
write, or registration, is needed for each VCPU. The interval between
Fields have the following meanings:
- version: a sequence counter. In other words, guest has to check
+ version:
+ a sequence counter. In other words, guest has to check
this field before and after grabbing time information and make
sure they are both equal and even. An odd version indicates an
in-progress update.
- flags: At this point, always zero. May be used to indicate
+ flags:
+ At this point, always zero. May be used to indicate
changes in this structure in the future.
- steal: the amount of time in which this vCPU did not run, in
+ steal:
+ the amount of time in which this vCPU did not run, in
nanoseconds. Time during which the vcpu is idle, will not be
reported as steal time.
- preempted: indicate the vCPU who owns this struct is running or
+ preempted:
+ indicate the vCPU who owns this struct is running or
not. Non-zero values mean the vCPU has been preempted. Zero
means the vCPU is not preempted. NOTE, it is always zero if the
the hypervisor doesn't support this field.
-MSR_KVM_EOI_EN: 0x4b564d04
- data: Bit 0 is 1 when PV end of interrupt is enabled on the vcpu; 0
+MSR_KVM_EOI_EN:
+ 0x4b564d04
+
+data:
+ Bit 0 is 1 when PV end of interrupt is enabled on the vcpu; 0
when disabled. Bit 1 is reserved and must be zero. When PV end of
interrupt is enabled (bit 0 set), bits 63-2 hold a 4-byte aligned
physical address of a 4 byte memory area which must be in guest RAM and
clear it using a single CPU instruction, such as test and clear, or
compare and exchange.
-MSR_KVM_POLL_CONTROL: 0x4b564d05
+MSR_KVM_POLL_CONTROL:
+ 0x4b564d05
+
Control host-side polling.
- data: Bit 0 enables (1) or disables (0) host-side HLT polling logic.
+data:
+ Bit 0 enables (1) or disables (0) host-side HLT polling logic.
KVM guests can request the host not to poll on HLT, for example if
they are performing polling themselves.
-
OSDN Git Service
