Re: [PATCH v8 1/7] target/i386/kvm: set KVM_PMU_CAP_DISABLE if "-pmu" is configured

[Sandipan Das <sandipan.das@amd.com>]

On 01-10-2026 14:02, Michael Tokarev wrote:
> On 12/30/25 10:42, Dongli Zhang wrote:
>> 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>
>> Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
>> Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
>> Reviewed-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
> 
> This is commit 4f0dd09e61b080c27589fe35b575503783c5a256 (v10.2.0-1114-g4f0dd09e61b)
> in the master branch now.
> 
> This change seem to broke booting windows 10/11 on an AMD host, in paticular
> with -cpu EPYC-Rome-v4.  It were initially reported in debian qemu bug tracker,
> and I verified and bisected the issue on my AMD desktop machine (which is AMD
> Ryzen 7 5700G, Zen 3.
> 
> When booting windows11 VM with -cpu EPYC-Rome-v4 -enable-kvm, the
> guest enters tight CPU loop while displaying a boot screen, before
> it starts showing up the rotating circle (which shows boot progress).
> 
> Before this patch, it boots ok.
> 
> There's no other fancy options, just
> 
>  qemu-system-x86_64 -m 2G -enable-kvm -cpu EPYC-Rome-v4 -smp 2
> 
> (I'm replying to the original email message with all original recipients,
> hope it's okay).
> 
> Can someone please take a look?
> 

What happens if you use "-cpu EPYC-Rome-v4,+pmu"?