linux-kernel - Re: [PATCH 2/3] KVM: x86: Remove use of apicv_update

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Message-ID: <30fc469b5b2ec5e2d6703979a0d09ad0a9df29e1.camel@redhat.com>
Date: Mon, 03 Feb 2025 21:00:05 -0500
From: Maxim Levitsky <mlevitsk@...hat.com>
To: "Naveen N Rao (AMD)" <naveen@...nel.org>, kvm@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Cc: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini
 <pbonzini@...hat.com>,  Suravee Suthikulpanit
 <suravee.suthikulpanit@....com>, Vasant Hegde <vasant.hegde@....com>,
 Vitaly Kuznetsov <vkuznets@...hat.com>
Subject: Re: [PATCH 2/3] KVM: x86: Remove use of apicv_update_lock when
 toggling guest debug state

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@...hat.com>

Best regards,
	Maxim Levitsky

> 
> Signed-off-by: Naveen N Rao (AMD) <naveen@...nel.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,