Move the vAPIC offset adjustments done in the APIC-write trap path from
common x86 to VMX in anticipation of using the nodecode path for SVM's
AVIC. The adjustment reflects hardware behavior, i.e. it's technically a
property of VMX, no common x86. SVM's AVIC behavior is identical, so
it's a bit of a moot point, the goal is purely to make it easier to
understand why the adjustment is ok.
No functional change intended.
Signed-off-by: Sean Christopherson <[email protected]>
---
arch/x86/kvm/lapic.c | 3 ---
arch/x86/kvm/vmx/vmx.c | 11 +++++++++--
2 files changed, 9 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 4662469240bc..fbce455a9d17 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2188,9 +2188,6 @@ void kvm_apic_write_nodecode(struct kvm_vcpu *vcpu, u32 offset)
{
u32 val = 0;
- /* hw has done the conditional check and inst decode */
- offset &= 0xff0;
-
kvm_lapic_reg_read(vcpu->arch.apic, offset, 4, &val);
/* TODO: optimize to just emulate side effect w/o one more write */
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index b1165bb13a5a..1b135473677b 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -5302,9 +5302,16 @@ static int handle_apic_eoi_induced(struct kvm_vcpu *vcpu)
static int handle_apic_write(struct kvm_vcpu *vcpu)
{
unsigned long exit_qualification = vmx_get_exit_qual(vcpu);
- u32 offset = exit_qualification & 0xfff;
- /* APIC-write VM exit is trap-like and thus no need to adjust IP */
+ /*
+ * APIC-write VM-Exit is trap-like, KVM doesn't need to advance RIP and
+ * hardware has done any necessary aliasing, offset adjustments, etc...
+ * for the access. I.e. the correct value has already been written to
+ * the vAPIC page for the correct 16-byte chunk. KVM needs only to
+ * retrieve the register value and emulate the access.
+ */
+ u32 offset = exit_qualification & 0xff0;
+
kvm_apic_write_nodecode(vcpu, offset);
return 1;
}
--
2.35.0.263.gb82422642f-goog
>--- a/arch/x86/kvm/vmx/vmx.c
>+++ b/arch/x86/kvm/vmx/vmx.c
>@@ -5302,9 +5302,16 @@ static int handle_apic_eoi_induced(struct kvm_vcpu *vcpu)
> static int handle_apic_write(struct kvm_vcpu *vcpu)
> {
> unsigned long exit_qualification = vmx_get_exit_qual(vcpu);
>- u32 offset = exit_qualification & 0xfff;
>
>- /* APIC-write VM exit is trap-like and thus no need to adjust IP */
>+ /*
>+ * APIC-write VM-Exit is trap-like, KVM doesn't need to advance RIP and
>+ * hardware has done any necessary aliasing, offset adjustments, etc...
>+ * for the access. I.e. the correct value has already been written to
>+ * the vAPIC page for the correct 16-byte chunk. KVM needs only to
>+ * retrieve the register value and emulate the access.
>+ */
>+ u32 offset = exit_qualification & 0xff0;
Can we take this opportunity to remove offset/exit_qualification?
They are used just once.
>+
> kvm_apic_write_nodecode(vcpu, offset);
> return 1;
> }
>--
>2.35.0.263.gb82422642f-goog
>
On Tue, Feb 15, 2022, Chao Gao wrote:
> >--- a/arch/x86/kvm/vmx/vmx.c
> >+++ b/arch/x86/kvm/vmx/vmx.c
> >@@ -5302,9 +5302,16 @@ static int handle_apic_eoi_induced(struct kvm_vcpu *vcpu)
> > static int handle_apic_write(struct kvm_vcpu *vcpu)
> > {
> > unsigned long exit_qualification = vmx_get_exit_qual(vcpu);
> >- u32 offset = exit_qualification & 0xfff;
> >
> >- /* APIC-write VM exit is trap-like and thus no need to adjust IP */
> >+ /*
> >+ * APIC-write VM-Exit is trap-like, KVM doesn't need to advance RIP and
> >+ * hardware has done any necessary aliasing, offset adjustments, etc...
> >+ * for the access. I.e. the correct value has already been written to
> >+ * the vAPIC page for the correct 16-byte chunk. KVM needs only to
> >+ * retrieve the register value and emulate the access.
> >+ */
> >+ u32 offset = exit_qualification & 0xff0;
>
> Can we take this opportunity to remove offset/exit_qualification?
> They are used just once.
Definitely should have dropped exit_qualification, not sure why I didn't.
I'd prefer to keep offset to document what is held in vmcs.EXIT_QUALIFICATION
without having to add an explicit comment.