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

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Date:   Tue, 21 Mar 2023 10:43:24 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Jim Mattson <jmattson@...gle.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 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