linux-kernel - Re: [PATCH] KVM: SVM: Fix svm the vmexit error

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Date:   Mon, 02 Mar 2020 13:54:15 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Haiwei Li <lihaiwei.kernel@...il.com>
Cc:     hpa@...or.com, bp@...en8.de,
        "mingo\@redhat.com" <mingo@...hat.com>,
        "tglx\@linutronix.de" <tglx@...utronix.de>,
        "joro\@8bytes.org" <joro@...tes.org>, jmattson@...gle.com,
        wanpengli@...cent.com,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        "pbonzini\@redhat.com" <pbonzini@...hat.com>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
        kvm@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH] KVM: SVM: Fix svm the vmexit error_code of WRMSR

Haiwei Li <lihaiwei.kernel@...il.com> writes:

>  From 1f755f75dfd73ad7cabb0e0f43e9993dd9f69120 Mon Sep 17 00:00:00 2001
> From: Haiwei Li <lihaiwei@...cent.com>
> Date: Mon, 2 Mar 2020 19:19:59 +0800
> Subject: [PATCH] KVM: SVM: Fix svm the vmexit error_code of WRMSR
>
> In svm, exit_code of write_msr is not EXIT_REASON_MSR_WRITE which
> belongs to vmx.

EXIT_REASON_MSR_WRITE is '32', in SVM this corresponds to
SVM_EXIT_READ_DR0. There were issues I guess. Or did you only detect
that the fastpath is not working?

>
> According to amd manual, SVM_EXIT_MSR(7ch) is the exit_code of VMEXIT_MSR
> due to RDMSR or WRMSR access to protected MSR. Additionally, the processor
> indicates in the VMCB's EXITINFO1 whether a RDMSR(EXITINFO1=0) or
> WRMSR(EXITINFO1=1) was intercepted.
>
> Signed-off-by: Haiwei Li <lihaiwei@...cent.com>

Fixes: 1e9e2622a149 ("KVM: VMX: FIXED+PHYSICAL mode single target IPI fastpath")

> ---
>   arch/x86/kvm/svm.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index fd3fc9f..ef71755 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -6296,7 +6296,8 @@ static void svm_handle_exit_irqoff(struct kvm_vcpu
> *vcpu,
>          enum exit_fastpath_completion *exit_fastpath)
>   {
>          if (!is_guest_mode(vcpu) &&
> -               to_svm(vcpu)->vmcb->control.exit_code ==
> EXIT_REASON_MSR_WRITE)

There is an extra newline here (in case it's not just me).

> +               (to_svm(vcpu)->vmcb->control.exit_code == SVM_EXIT_MSR) &&
> +               (to_svm(vcpu)->vmcb->control.exit_info_1 & 1))

Could we add defines for '1' and '0', like
SVM_EXITINFO_MSR_WRITE/SVM_EXITINFO_MSR_READ maybe?

>                  *exit_fastpath = handle_fastpath_set_msr_irqoff(vcpu);
>   }
>
> --
> 1.8.3.1
>

-- 
Vitaly