On Wed, Oct 4, 2023 at 12:59 AM Borislav Petkov <bp@xxxxxxxxx> wrote: > > On Tue, Oct 03, 2023 at 07:44:51PM -0700, Jim Mattson wrote: > > The business of declaring breaking changes to the architectural > > specification in a CPUID bit has never made much sense to me. > > How else should they be expressed then? > > In some flaky PDF which changes URLs whenever the new corporate CMS gets > installed? > > Or we should do f/m/s matching which doesn't make any sense for VMs? > > When you think about it, CPUID is the best thing we have. Every time a new defeature bit is introduced, it breaks existing hypervisors, because no one can predict ahead of time that these bits have to be passed through. I wonder if we could convince x86 CPU vendors to put all defeature bits under a single leaf, so that we can just set the entire leaf to all 1's in KVM_GET_SUPPORTED_CPUID.
