linux-kernel - Re: [PATCH 0/3] KVM: support the cpu feature FLUSH

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Message-ID: <CALMp9eQ+U3SLt=KOti=xF2cXCV0oJSpMOGXfj9uhe7m=_57R+Q@mail.gmail.com>
Date:   Tue, 21 Mar 2023 11:30:01 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Emanuele Giuseppe Esposito <eesposit@...hat.com>,
        kvm@...r.kernel.org, Ben Serebrin <serebrin@...gle.com>,
        Peter Shier <pshier@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Maxim Levitsky <mlevitsk@...hat.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] KVM: support the cpu feature FLUSH_L1D

On Tue, Mar 21, 2023 at 2:43 AM Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> On Mon, Mar 20, 2023 at 5:52 PM Jim Mattson <jmattson@...gle.com> wrote:
> > > Patch 1 and 2 are just taken and refactored from Jim Mattison's serie that it
> > > seems was lost a while ago:
> > > https://patchwork.kernel.org/project/kvm/patch/20180814173049.21756-1-jmattson@google.com/
> > >
> > > I thought it was worth re-posting them.
> >
> > What has changed since the patches were originally posted, and Konrad
> > dissed them?
>
> What has changed is that the reporting of mmio_stale_data now
> piggybacks on flush_l1d as well.
>
>         if ((ia32_cap & ARCH_CAP_FB_CLEAR) ||
>             (boot_cpu_has(X86_FEATURE_MD_CLEAR) &&
>              boot_cpu_has(X86_FEATURE_FLUSH_L1D) &&
>              !(ia32_cap & ARCH_CAP_MDS_NO)))
>                 mmio_mitigation = MMIO_MITIGATION_VERW;
>         else
>                 mmio_mitigation = MMIO_MITIGATION_UCODE_NEEDED;
>
> Maybe Intel only defines CPUID bits after a firstborn has been
> sacriificed to the microcode gods?
>
> Paolo
>

Ha!

As I wrote way back when, "It is more forward-thinking to provide this
capability than it is not to."

I feel vindicated. :)