Re: [PATCH 0/3] KVM: support the cpu feature FLUSH_L1D

[Paolo Bonzini]

On Mon, Mar 20, 2023 at 5:52 PM Jim Mattson <jmattson@xxxxxxxxxx> 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@xxxxxxxxxx/
> >
> > 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