Re: [RFT PATCH v2 2/2] target/i386: add compatibility property for pdcm feature

[Zhao Liu <zhao1.liu@intel.com>]

On Tue, Sep 23, 2025 at 12:41:36PM +0200, Paolo Bonzini wrote:
> Date: Tue, 23 Sep 2025 12:41:36 +0200
> From: Paolo Bonzini <pbonzini@redhat.com>
> Subject: [RFT PATCH v2 2/2] target/i386: add compatibility property for
>  pdcm feature
> X-Mailer: git-send-email 2.51.0
> 
> From: Hector Cao <hector.cao@canonical.com>
> 
> The pdcm feature is supposed to be disabled when PMU is not
> available. Up until v10.1, pdcm feature is enabled even when PMU
> is off. This behavior has been fixed but this change breaks the
> migration of VMs that are run with QEMU < 10.0 and expect the pdcm
> feature to be enabled on the destination host.
> 
> This commit restores the legacy behavior for machines with version
> prior to 10.1 to allow the migration from older QEMU to QEMU 10.1.
> 
> Signed-off-by: Hector Cao <hector.cao@canonical.com>
> Link: https://lore.kernel.org/r/20250910115733.21149-3-hector.cao@canonical.com
> Fixes: e68ec298090 ("i386/cpu: Move adjustment of CPUID_EXT_PDCM before feature_dependencies[] check", 2025-06-20)
> [Move property from migration object to CPU. - Paolo]
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  target/i386/cpu.h |  6 ++++++
>  hw/i386/pc.c      |  1 +
>  target/i386/cpu.c | 15 ++++++++++++---
>  3 files changed, 19 insertions(+), 3 deletions(-)

Reviewed-by: Zhao Liu <zhao1.liu@intel.com>