On Fri, Jun 2, 2023 at 12:18 AM Gao Shiyuan <gaoshiyuan@xxxxxxxxx> wrote:
>
> From: Shiyuan Gao <gaoshiyuan@xxxxxxxxx>
>
> When live-migrate VM on icelake microarchitecture, if the source
> host kernel before commit 2e8cd7a3b828 ("kvm: x86: limit the maximum
> number of vPMU fixed counters to 3") and the dest host kernel after this
> commit, the migration will fail.
>
> The source VM's CPUID.0xA.edx[0..4]=4 that is reported by KVM and
> the IA32_PERF_GLOBAL_CTRL MSR is 0xf000000ff. However the dest VM's
> CPUID.0xA.edx[0..4]=3 and the IA32_PERF_GLOBAL_CTRL MSR is 0x7000000ff.
> This inconsistency leads to migration failure.
>
> The QEMU limits the maximum number of vPMU fixed counters to 3, so ignore
> the check of IA32_PERF_GLOBAL_CTRL bit35.
Today, the fixed counters are limited to 3, but I hope we get support
for top down slots soon.
Perhaps this inconsistency is best addressed with a quirk?
