On Mon, Apr 29, 2024, Alejandro Jimenez wrote:
> Even when APICv/AVIC is active, certain guest accesses to its local APIC(s)
> cannot be fully accelerated, and cause a #VMEXIT to allow the VMM to
> emulate the behavior and side effects. Expose a counter stat for these
> specific #VMEXIT types.
>
> Suggested-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Signed-off-by: Alejandro Jimenez <alejandro.j.jimenez@xxxxxxxxxx>
> ---
> arch/x86/include/asm/kvm_host.h | 1 +
> arch/x86/kvm/svm/avic.c | 7 +++++++
> arch/x86/kvm/vmx/vmx.c | 2 ++
> arch/x86/kvm/x86.c | 1 +
> 4 files changed, 11 insertions(+)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index e7e3213cefae..388979dfe9f3 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1576,6 +1576,7 @@ struct kvm_vcpu_stat {
> u64 guest_mode;
> u64 notify_window_exits;
> u64 apicv_active;
> + u64 apicv_unaccelerated_inj;
The stat name doesn't match the changelog or the code. The AVIC updates in
avic_incomplete_ipi_interception() are unaccelerated _injection_, they're
unaccelarated _delivery_. And in those cases, the fact that delivery wasn't
accelerated is relatively uninteresting in most cases.
And avic_unaccelerated_access_interception() and handle_apic_write() don't
necessarily have anything to do with injection.
On the flip side, the slow paths for {svm,vmx}_deliver_interrupt() are very
explicitly unnaccelerated injection.
It's not entirely clear from the changelog what the end goal of this stat is.
A singular stat for all APICv/AVIC access VM-Exits seems uninteresting, as such
a stat essentially just captures that the guest is active. Maaaybe someone could
glean info from comparing two VMs, but even that is dubious. E.g. if a guest is
doing something function and generating a lot of avic_incomplete_ipi_interception()
exits, those will likely be in the noise due to the total volume of other AVIC
exits.
> };
>
> struct x86_instruction_info;
> diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
> index 4b74ea91f4e6..274041d3cf66 100644
> --- a/arch/x86/kvm/svm/avic.c
> +++ b/arch/x86/kvm/svm/avic.c
> @@ -517,6 +517,8 @@ int avic_incomplete_ipi_interception(struct kvm_vcpu *vcpu)
> kvm_apic_write_nodecode(vcpu, APIC_ICR);
> else
> kvm_apic_send_ipi(apic, icrl, icrh);
> +
> + ++vcpu->stat.apicv_unaccelerated_inj;
> break;
> case AVIC_IPI_FAILURE_TARGET_NOT_RUNNING:
> /*
> @@ -525,6 +527,8 @@ int avic_incomplete_ipi_interception(struct kvm_vcpu *vcpu)
> * vcpus. So, we just need to kick the appropriate vcpu.
> */
> avic_kick_target_vcpus(vcpu->kvm, apic, icrl, icrh, index);
> +
> + ++vcpu->stat.apicv_unaccelerated_inj;
> break;
> case AVIC_IPI_FAILURE_INVALID_BACKING_PAGE:
> WARN_ONCE(1, "Invalid backing page\n");
> @@ -704,6 +708,9 @@ int avic_unaccelerated_access_interception(struct kvm_vcpu *vcpu)
>
> trace_kvm_avic_unaccelerated_access(vcpu->vcpu_id, offset,
> trap, write, vector);
> +
> + ++vcpu->stat.apicv_unaccelerated_inj;
> +
> if (trap) {
> /* Handling Trap */
> WARN_ONCE(!write, "svm: Handling trap read.\n");
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index f10b5f8f364b..a7487f12ded1 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -5657,6 +5657,8 @@ static int handle_apic_write(struct kvm_vcpu *vcpu)
> {
> unsigned long exit_qualification = vmx_get_exit_qual(vcpu);
>
> + ++vcpu->stat.apicv_unaccelerated_inj;
> +
> /*
> * APIC-write VM-Exit is trap-like, KVM doesn't need to advance RIP and
> * hardware has done any necessary aliasing, offset adjustments, etc...
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 03cb933920cb..c8730b0fac87 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -307,6 +307,7 @@ const struct _kvm_stats_desc kvm_vcpu_stats_desc[] = {
> STATS_DESC_IBOOLEAN(VCPU, guest_mode),
> STATS_DESC_COUNTER(VCPU, notify_window_exits),
> STATS_DESC_IBOOLEAN(VCPU, apicv_active),
> + STATS_DESC_COUNTER(VCPU, apicv_unaccelerated_inj),
> };
>
> const struct kvm_stats_header kvm_vcpu_stats_header = {
> --
> 2.39.3
>
