Re: [PATCH v2 3/5] KVM: x86/pmu: Refresh Host-Only/Guest-Only eventsel at nested transitions

[Yosry Ahmed]

On Thu, Jan 29, 2026 at 03:28:08PM -0800, Jim Mattson wrote:
> Add amd_pmu_refresh_host_guest_eventsel_hw() to recalculate eventsel_hw for
> all PMCs based on the current vCPU state. This is needed because Host-Only
> and Guest-Only counters must be enabled/disabled at:
> 
>   - SVME changes: When EFER.SVME is modified, counters with Guest-Only bits
>     need their hardware enable state updated.
> 
>   - Nested transitions: When entering or leaving guest mode, Host-Only
>     counters should be disabled/enabled and Guest-Only counters should be
>     enabled/disabled accordingly.
> 
> Introduce svm_enter_guest_mode() and svm_leave_guest_mode() wrappers that
> call enter_guest_mode()/leave_guest_mode() followed by the PMU refresh,
> ensuring the PMU state stays synchronized with guest mode transitions.
> 
> Signed-off-by: Jim Mattson <jmattson@xxxxxxxxxx>
> ---
>  arch/x86/kvm/svm/nested.c |  6 +++---
>  arch/x86/kvm/svm/pmu.c    | 12 ++++++++++++
>  arch/x86/kvm/svm/svm.c    |  2 ++
>  arch/x86/kvm/svm/svm.h    | 17 +++++++++++++++++
>  4 files changed, 34 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index de90b104a0dd..a7d1901f256b 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -757,7 +757,7 @@ static void nested_vmcb02_prepare_control(struct vcpu_svm *svm,
>  	nested_svm_transition_tlb_flush(vcpu);
>  
>  	/* Enter Guest-Mode */
> -	enter_guest_mode(vcpu);
> +	svm_enter_guest_mode(vcpu);

FWIW, I think this name is a bit confusing because we also have
enter_svm_guest_mode(). So we end up with:

enter_svm_guest_mode() -> nested_vmcb02_prepare_control() ->
svm_enter_guest_mode() -> enter_guest_mode()

I actually have another proposed change [1] that moves
enter_guest_mode() directly into enter_svm_guest_mode(), so the sequence
would end up being:

enter_svm_guest_mode() -> svm_enter_guest_mode() -> enter_guest_mode()

[1] https://lore.kernel.org/kvm/20260115011312.3675857-9-yosry.ahmed@xxxxxxxxx/