linux-kernel - Re: [PATCH v3] KVM: VMX: do not disable interception for MSR_IA32_SPEC

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Date:   Wed, 25 May 2022 10:46:43 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     Jon Kohler <jon@...anix.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Waiman Long <longman@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] KVM: VMX: do not disable interception for
 MSR_IA32_SPEC_CTRL on eIBRS

On Wed, May 25, 2022 at 10:14 AM Jon Kohler <jon@...anix.com> wrote:
>
>
>
> > On May 25, 2022, at 1:04 PM, Sean Christopherson <seanjc@...gle.com> wrote:
> >
> > 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 = data;
> >> -            if (!data)
> >> +
> >> +            /*
> >> +             * Disable interception on the first non-zero write, unless the
> >> +             * guest is hosted on an eIBRS system and setting only
> >
> > The "unless guest is hosted on an eIBRS system" blurb is wrong and doesn't match
>
> Ah right, thanks for catching that
>
> > the code.  Again, it's all about whether eIBRS is advertised to the guest.  With
> > some other minor tweaking to wrangle the comment to 80 chars...
>
> RE 80 chars - quick question (and forgive the silly question here), but how are you
> counting that? I’ve got my editor cutting at 79 cols, where tab size 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. :-)