Re: [PATCH v2 04/10] target/i386/kvm: set KVM_PMU_CAP_DISABLE if "-pmu" is configured

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

On Sun, Mar 02, 2025 at 02:00:12PM -0800, Dongli Zhang wrote:
> Date: Sun,  2 Mar 2025 14:00:12 -0800
> From: Dongli Zhang <dongli.zhang@oracle.com>
> Subject: [PATCH v2 04/10] target/i386/kvm: set KVM_PMU_CAP_DISABLE if
>  "-pmu" is configured
> X-Mailer: git-send-email 2.43.5
> 
> Although AMD PERFCORE and PerfMonV2 are removed when "-pmu" is configured,
> there is no way to fully disable KVM AMD PMU virtualization. Neither
> "-cpu host,-pmu" nor "-cpu EPYC" achieves this.
> 
> As a result, the following message still appears in the VM dmesg:
> 
> [    0.263615] Performance Events: AMD PMU driver.
> 
> However, the expected output should be:
> 
> [    0.596381] Performance Events: PMU not available due to virtualization, using software events only.
> [    0.600972] NMI watchdog: Perf NMI watchdog permanently disabled
> 
> This occurs because AMD does not use any CPUID bit to indicate PMU
> availability.
> 
> To address this, KVM_CAP_PMU_CAPABILITY is used to set KVM_PMU_CAP_DISABLE
> when "-pmu" is configured.
> 
> Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
> ---
> Changed since v1:
>   - Switch back to the initial implementation with "-pmu".
> https://lore.kernel.org/all/20221119122901.2469-3-dongli.zhang@oracle.com
>   - Mention that "KVM_PMU_CAP_DISABLE doesn't change the PMU behavior on
>     Intel platform because current "pmu" property works as expected."
> 
>  target/i386/kvm/kvm.c | 31 +++++++++++++++++++++++++++++++
>  1 file changed, 31 insertions(+)

Overall LGTM. And with Xiaoyao's comment fixed :-)

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

Thanks,
Zhao