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References: <20220520204115.67580-1-jon@nutanix.com> <Yo5hmcdRvE1UrI4y@google.com>
 <3C8F5313-2830-46E3-A512-CFA4A24C24D7@nutanix.com>
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From:   Jim Mattson <jmattson@google.com>
Date:   Wed, 25 May 2022 10:46:43 -0700
Message-ID: <CALMp9eT2=tEijnxUxFfv-1r5LJG4MyezqjnTsrysjuWGeko7_w@mail.gmail.com>
Subject: Re: [PATCH v3] KVM: VMX: do not disable interception for
 MSR_IA32_SPEC_CTRL on eIBRS
To:     Jon Kohler <jon@nutanix.com>
Cc:     Sean Christopherson <seanjc@google.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Joerg Roedel <joro@8bytes.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "x86@kernel.org" <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Waiman Long <longman@redhat.com>,
        Kees Cook <keescook@chromium.org>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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On Wed, May 25, 2022 at 10:14 AM Jon Kohler <jon@nutanix.com> wrote:
>
>
>
> > On May 25, 2022, at 1:04 PM, Sean Christopherson <seanjc@google.com> wr=
ote:
> >
> > On Fri, May 20, 2022, Jon Kohler wrote:
> >> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> >> index 610355b9ccce..1c725d17d984 100644
> >> --- a/arch/x86/kvm/vmx/vmx.c
> >> +++ b/arch/x86/kvm/vmx/vmx.c
> >> @@ -2057,20 +2057,32 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, =
struct msr_data *msr_info)
> >>                      return 1;
> >>
> >>              vmx->spec_ctrl =3D data;
> >> -            if (!data)
> >> +
> >> +            /*
> >> +             * Disable interception on the first non-zero write, unle=
ss the
> >> +             * guest is hosted on an eIBRS system and setting only
> >
> > The "unless guest is hosted on an eIBRS system" blurb is wrong and does=
n't match
>
> Ah right, thanks for catching that
>
> > the code.  Again, it's all about whether eIBRS is advertised to the gue=
st.  With
> > some other minor tweaking to wrangle the comment to 80 chars...
>
> RE 80 chars - quick question (and forgive the silly question here), but h=
ow are you
> counting that? I=E2=80=99ve got my editor cutting at 79 cols, where tab s=
ize is accounted
> for as 4 cols, so the longest line on my side for this patch is 72-73 or =
so.

Tab stops are every 8 characters. :-)