Re: [PATCH 2/3] KVM: x86: Remove use of apicv_update_lock when toggling guest debug state

Maxim Levitsky
2025-02-04T02:00:12Z

On Mon, 2025-02-03 at 22:33 +0530, Naveen N Rao (AMD) wrote:
> apicv_update_lock is not required when querying the state of guest
> debug in all the vcpus. Remove usage of the same, and switch to
> kvm_set_or_clear_apicv_inhibit() helper to simplify the code.

It might be worth to mention that the reason why the lock is not needed,
is because kvm_vcpu_ioctl from which this function is called takes 'vcpu->mutex'
and thus concurrent execution of this function is not really possible.

Besides this:

Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>

Best regards,
Maxim Levitsky

>
> Signed-off-by: Naveen N Rao (AMD) <naveen@kernel.org>
> ---
> arch/x86/kvm/x86.c | 9 ++-------
> 1 file changed, 2 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index b2d9a16fd4d3..11235e91ae90 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -12038,19 +12038,14 @@ static void kvm_arch_vcpu_guestdbg_update_apicv_inhibit(struct kvm *kvm)
> struct kvm_vcpu *vcpu;
> unsigned long i;
>
> - if (!enable_apicv)
> - return;
> -
> - down_write(&kvm->arch.apicv_update_lock);
> -
> kvm_for_each_vcpu(i, vcpu, kvm) {
> if (vcpu->guest_debug & KVM_GUESTDBG_BLOCKIRQ) {
> set = true;
> break;
> }
> }
> - __kvm_set_or_clear_apicv_inhibit(kvm, APICV_INHIBIT_REASON_BLOCKIRQ, set);
> - up_write(&kvm->arch.apicv_update_lock);
> +
> + kvm_set_or_clear_apicv_inhibit(kvm, APICV_INHIBIT_REASON_BLOCKIRQ, set);
> }
>
> int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,