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-rw-r--r--Documentation/kvm/msr.txt36
1 files changed, 35 insertions, 1 deletions
diff --git a/Documentation/kvm/msr.txt b/Documentation/kvm/msr.txt
index 8ddcfe84c09..d079aed27e0 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 +150,38 @@ 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 5-2 are reserved and should be zero. Bit 0 is 1
+ when asynchronous page faults are enabled on the vcpu 0 when
+ disabled. Bit 2 is 1 if asynchronous page faults can be injected
+ when vcpu is in cpl == 0.
+
+ 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.