Re: [PATCH 4/4] x86/tsx: Add cmdline tsx=fake to not clear CPUID bits RTM and HLE

[Jim Mattson]

On Wed, Jul 7, 2021 at 10:08 AM Eduardo Habkost <ehabkost@xxxxxxxxxx> wrote:
>
> On Wed, Jul 7, 2021 at 12:42 PM Jim Mattson <jmattson@xxxxxxxxxx> wrote:
> >
> > On Wed, Jul 7, 2021 at 8:09 AM Eduardo Habkost <ehabkost@xxxxxxxxxx> 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?

This is my ongoing rant about KVM_GET_SUPPORTED_CPUID.