Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Vitaly Kuznetsov <vkuznets@redhat.com>
To:     Wanpeng Li <kernellwp@gmail.com>, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org
Cc:     Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        "Paul K ." <kronenpj@kronenpj.dyndns.org>, <stable@vger.kernel.org>
Subject: Re: [PATCH 1/3] KVM: SVM: Get rid of handle_fastpath_set_msr_irqoff()
In-Reply-To: <1599620043-12908-1-git-send-email-wanpengli@tencent.com>
References: <1599620043-12908-1-git-send-email-wanpengli@tencent.com>
Date:   Wed, 09 Sep 2020 10:23:20 +0200
Message-ID: <87h7s7mk93.fsf@vitty.brq.redhat.com>
MIME-Version: 1.0
Content-Type: text/plain
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Wanpeng Li <kernellwp@gmail.com> writes:

> From: Wanpeng Li <wanpengli@tencent.com>
>
> Analysis from Sean:
>
>  | svm->next_rip is reset in svm_vcpu_run() only after calling 
>  | svm_exit_handlers_fastpath(), which will cause SVM's 
>  | skip_emulated_instruction() to write a stale RIP.
>  

This should only happen when svm->vmcb->control.next_rip is not set by
hardware as skip_emulated_instruction() itself sets 'svm->next_rip'
otherwise, right?

> Let's get rid of handle_fastpath_set_msr_irqoff() in svm_exit_handlers_fastpath()
> to have a quick fix.

which in the light of the whole seeries seems to be appropriate, so:

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>

>
> Reported-by: Paul K. <kronenpj@kronenpj.dyndns.org>
> Suggested-by: Sean Christopherson <sean.j.christopherson@intel.com>
> Cc: Paul K. <kronenpj@kronenpj.dyndns.org>
> Cc: <stable@vger.kernel.org> # v5.8-rc1+
> Fixes: 404d5d7bff0d (KVM: X86: Introduce more exit_fastpath_completion enum values)
> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> ---
>  arch/x86/kvm/svm/svm.c | 5 -----
>  1 file changed, 5 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 19e622a..c61bc3b 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -3349,11 +3349,6 @@ static void svm_cancel_injection(struct kvm_vcpu *vcpu)
>  
>  static fastpath_t svm_exit_handlers_fastpath(struct kvm_vcpu *vcpu)
>  {
> -	if (!is_guest_mode(vcpu) &&
> -	    to_svm(vcpu)->vmcb->control.exit_code == SVM_EXIT_MSR &&
> -	    to_svm(vcpu)->vmcb->control.exit_info_1)
> -		return handle_fastpath_set_msr_irqoff(vcpu);
> -
>  	return EXIT_FASTPATH_NONE;
>  }

-- 
Vitaly