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SubjectRe: [PATCH 4/4] x86/tsx: Add cmdline tsx=fake to not clear CPUID bits RTM and HLE
On Wed, Jul 7, 2021 at 12:42 PM Jim Mattson <jmattson@google.com> wrote:
>
> On Wed, Jul 7, 2021 at 8:09 AM Eduardo Habkost <ehabkost@redhat.com> wrote:
> >
> > CCing libvir-list, Jiri Denemark, Michal Privoznik, so they are aware
> > that the definition of "supported CPU features" will probably become a
> > bit more complex in the future.
>
> Has there ever been a clear definition? Family, model, and stepping,
> for instance: are these the only values supported? That would make
> cross-platform migration impossible. What about the vendor string? Is
> that the only value supported? That would make cross-vendor migration
> impossible. For the maximum input value for basic CPUID information
> (CPUID.0H:EAX), is that the only value supported, or is it the maximum
> value supported? On the various individual feature bits, does a '1'
> imply that '0' is also supported, or is '1' the only value supported?
> What about the feature bits with reversed polarity (e.g.
> CPUID.(EAX=07H,ECX=0):EBX.FDP_EXCPTN_ONLY[bit 6])?
>
> This API has never made sense to me. I have no idea how to interpret
> what it is telling me.

Is this about GET_SUPPORTED_CPUID, QEMU's query-cpu-model-expansion &
related commands, or the libvirt CPU APIs?

--
Eduardo

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