KVM: Add PV MSR to enable asynchronous page faults delivery.

[linux-3.10.git] / Documentation / kvm / msr.txt

diff --git a/Documentation/kvm/msr.txt b/Documentation/kvm/msr.txt
index 8ddcfe84c09a3df07809015e47b5e5290fedc14f..e67b4a8783dfb0d9a28981f2b12230d52a1f9b30 100644 (file)
--- 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.