linux-kernel - Re: [PATCH] KVM: X86: Fix always skip to boost kernel lock holder candidate for SEV-ES guests

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Message-ID: <a5dc4068-050e-b651-2e8a-8e90164694a6@redhat.com>
Date:   Thu, 22 Apr 2021 12:34:34 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH] KVM: X86: Fix always skip to boost kernel lock holder
 candidate for SEV-ES guests

On 22/04/21 10:34, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@...cent.com>
> 
> Commit f1c6366e3043 ("KVM: SVM: Add required changes to support intercepts under
> SEV-ES") prevents hypervisor accesses guest register state when the guest is
> running under SEV-ES. The initial value of vcpu->arch.guest_state_protected
> is false, it will not be updated in preemption notifiers after this commit which
> means that the kernel spinlock lock holder will always be skipped to boost. Let's
> fix it by always treating preempted is in the guest kernel mode, false positive
> is better than skip completely.
> 
> Fixes: f1c6366e3043 (KVM: SVM: Add required changes to support intercepts under SEV-ES)
> Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
> ---
>   arch/x86/kvm/x86.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index d696a9f..e52ca09 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -11151,6 +11151,9 @@ bool kvm_arch_dy_has_pending_interrupt(struct kvm_vcpu *vcpu)
>   
>   bool kvm_arch_vcpu_in_kernel(struct kvm_vcpu *vcpu)
>   {
> +	if (vcpu->arch.guest_state_protected)
> +		return true;
> +
>   	return vcpu->arch.preempted_in_kernel;
>   }
>   
> 

Queued, thanks.

Paolo