On Tue, May 4, 2021 at 2:26 AM Alexander Graf <graf@xxxxxxxxxx> wrote: > > > > On 04.05.21 10:21, Paolo Bonzini wrote: > > > > On 04/05/21 10:15, Denis V. Lunev wrote: > >> As far as I understand only some testing within kernel now. > >> Though we have plans to expose it for QAPI as the series > >> in QEMU > >> [PATCH 1/2] qapi: fix error handling for x-vz-query-cpu-model-cpuid > >> [PATCH 2/2] qapi: blacklisted x-vz-query-cpu-model-cpuid in tests > >> is not coming in a good way. > >> The idea was to avoid manual code rework in QEMU and > >> expose collected model at least for debug. > > > > KVM_GET_CPUID2 as a VM ioctl cannot expose the whole truth about CPUID > > either, since it doesn't handle the TSX_CTRL_CPUID_CLEAR bit. Given > > that QEMU doesn't need KVM_GET_CPUID2; it only needs to save whatever it > > passed to KVM_SET_CPUID2. > > What if we instead deflect CPUID into user space so it can emulate it in > whatever way it likes? Is the performance difference going to be > relevant? Are people still using cpuid as barrier these days? What else would they use (in ring 3 code)? Sure, serialize is coming in Sapphire Rapids, but it will be 20+ years before kvm drops support for CPUs without serialize. > > Alex > > > > Amazon Development Center Germany GmbH > Krausenstr. 38 > 10117 Berlin > Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss > Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B > Sitz: Berlin > Ust-ID: DE 289 237 879 > >
