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.
>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'?
