[PATCH] KVM: x86: Use the correct size of struct kvm_vcpu_pv_apf_data and fix the documentation

Xiaoyao Li
2023-10-13T07:00:54Z

The size of struct kvm_vcpu_pv_apf_data is 68 bytes, not 64 bytes.
Fix the kvm_gfn_to_hva_cache_init() to use the correct size though KVM
only touches fist 8 bytes.

Fix the documentation and opportunistically refine the documentation.

Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
---
Documentation/virt/kvm/x86/msr.rst | 22 +++++++++++-----------
arch/x86/kvm/x86.c | 2 +-
2 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/Documentation/virt/kvm/x86/msr.rst b/Documentation/virt/kvm/x86/msr.rst
index 9315fc385fb0..27bcd49e46b9 100644
--- a/Documentation/virt/kvm/x86/msr.rst
+++ b/Documentation/virt/kvm/x86/msr.rst
@@ -192,9 +192,9 @@ MSR_KVM_ASYNC_PF_EN:
data:
Asynchronous page fault (APF) control MSR.

- 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. This memory is expected
- to hold a copy of the following structure::
+ Bits 63-6 hold 64-byte aligned physical address of a 68 bytes memory
+ area which must be in guest RAM. This memory is expected to hold a copy
+ of the following structure::

struct kvm_vcpu_pv_apf_data {
/* Used for 'page not present' events delivered via #PF */
@@ -220,7 +220,7 @@ data:
#PF exception. During delivery of these events APF CR2 register contains
a token that will be used to notify the guest when missing page becomes
available. Also, to make it possible to distinguish between real #PF and
- APF, first 4 bytes of 64 byte memory location ('flags') will be written
+ APF, first 4 bytes of 68 byte memory location ('flags') will be written
to by the hypervisor at the time of injection. Only first bit of 'flags'
is currently supported, when set, it indicates that the guest is dealing
with asynchronous 'page not present' event. If during a page fault APF
@@ -232,14 +232,14 @@ data:
as regular page fault, guest must reset 'flags' to '0' before it does
something that can generate normal page fault.

- Bytes 5-7 of 64 byte memory location ('token') will be written to by the
+ Bytes 4-7 of 68 byte memory location ('token') will be written to by the
hypervisor at the time of APF 'page ready' event injection. The content
- of these bytes is a token which was previously delivered as 'page not
- present' event. The event indicates the page in now available. Guest is
- supposed to write '0' to 'token' when it is done handling 'page ready'
- event and to write 1' to MSR_KVM_ASYNC_PF_ACK after clearing the location;
- writing to the MSR forces KVM to re-scan its queue and deliver the next
- pending notification.
+ of these bytes is a token which was previously delivered in CR2 as
+ 'page not present' event. The event indicates the page is now available.
+ Guest is supposed to write '0' to 'token' when it is done handling
+ 'page ready' event and to write '1' to MSR_KVM_ASYNC_PF_ACK after
+ clearing the location; writing to the MSR forces KVM to re-scan its
+ queue and deliver the next pending notification.

Note, MSR_KVM_ASYNC_PF_INT MSR specifying the interrupt vector for 'page
ready' APF delivery needs to be written to before enabling APF mechanism
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 9f18b06bbda6..fc253d54cbd3 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3427,7 +3427,7 @@ static int kvm_pv_enable_async_pf(struct kvm_vcpu *vcpu, u64 data)
}

if (kvm_gfn_to_hva_cache_init(vcpu->kvm, &vcpu->arch.apf.data, gpa,
- sizeof(u64)))
+ sizeof(struct kvm_vcpu_pv_apf_data)))
return 1;

vcpu->arch.apf.send_user_only = !(data & KVM_ASYNC_PF_SEND_ALWAYS);

base-commit: 5804c19b80bf625c6a9925317f845e497434d6d3
--
2.34.1