On Wed, Jul 7, 2021 at 12:42 PM Jim Mattson [off-list ref] wrote:

On Wed, Jul 7, 2021 at 8:09 AM Eduardo Habkost [off-list ref] wrote:

quoted

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