On 8/21/2025 12:34 PM, Sohil Mehta wrote: > On 8/21/2025 6:15 AM, David Woodhouse wrote: > >> Hm. My test host is INTEL_HASWELL_X (0x63f). For reasons which are >> unclear to me, QEMU doesn't set bit 8 of 0x80000007 EDX unless I >> explicitly append ',+invtsc' to the existing '-cpu host' on its command >> line. So now my guest doesn't think it has X86_FEATURE_CONSTANT_TSC. >> > > Haswell should have X86_FEATURE_CONSTANT_TSC, so I would have expected > the guest bit to be set. Until now, X86_FEATURE_CONSTANT_TSC was set > based on the Family-model instead of the CPUID enumeration which may > have hid the issue. >
Correction: s/instead/as well as > From my initial look at the QEMU implementation, this seems intentional. > > QEMU considers Invariant TSC as un-migratable which prevents it from > being exposed to migratable guests (default). > target/i386/cpu.c: > [FEAT_8000_0007_EDX] > .unmigratable_flags = CPUID_APM_INVTSC, > > Can you please try '-cpu host,migratable=off'? This is mainly to verify. If confirmed, I am not sure what the long term solution should be.
