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Diffstat (limited to 'Documentation/kvm/msr.txt')
| -rw-r--r-- | Documentation/kvm/msr.txt | 35 |
1 files changed, 34 insertions, 1 deletions
diff --git a/Documentation/kvm/msr.txt b/Documentation/kvm/msr.txt index 8ddcfe84c09..e67b4a8783d 100644 --- a/Documentation/kvm/msr.txt +++ b/Documentation/kvm/msr.txt @@ -3,7 +3,6 @@ Glauber Costa <glommer@redhat.com>, Red Hat Inc, 2010 ===================================================== KVM makes use of some custom MSRs to service some requests. -At present, this facility is only used by kvmclock. Custom MSRs have a range reserved for them, that goes from 0x4b564d00 to 0x4b564dff. There are MSRs outside this area, @@ -151,3 +150,37 @@ MSR_KVM_SYSTEM_TIME: 0x12 return PRESENT; } else return NON_PRESENT; + +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 5-1 are reserved and should be zero. Bit 0 is 1 + when asynchronous page faults are enabled on the vcpu 0 when + disabled. + + First 4 byte of 64 byte memory location will be written to by + the hypervisor at the time of asynchronous page fault (APF) + injection to indicate type of asynchronous page fault. Value + of 1 means that the page referred to by the page fault is not + present. Value 2 means that the page is now available. Disabling + interrupt inhibits APFs. Guest must not enable interrupt + before the reason is read, or it may be overwritten by another + APF. Since APF uses the same exception vector as regular page + fault guest must reset the reason to 0 before it does + something that can generate normal page fault. If during page + fault APF reason is 0 it means that this is regular page + fault. + + During delivery of type 1 APF cr2 contains a token that will + be used to notify a guest when missing page becomes + available. When page becomes available type 2 APF is sent with + cr2 set to the token associated with the page. There is special + kind of token 0xffffffff which tells vcpu that it should wake + up all processes waiting for APFs and no individual type 2 APFs + will be sent. + + If APF is disabled while there are outstanding APFs, they will + not be delivered. + + Currently type 2 APF will be always delivered on the same vcpu as + type 1 was, but guest should not rely on that. |