Hi Zhao,
On 4/10/25 2:45 AM, Zhao Liu wrote:
> On Sun, Mar 30, 2025 at 06:32:29PM -0700, Dongli Zhang wrote:
>> Date: Sun, 30 Mar 2025 18:32:29 -0700
>> From: Dongli Zhang <dongli.zh...@oracle.com>
>> Subject: [PATCH v3 10/10] target/i386/kvm: don't stop Intel PMU counters
>> X-Mailer: git-send-email 2.43.5
>>
>> The kvm_put_msrs() sets the MSRs using KVM_SET_MSRS. The x86 KVM processes
>> these MSRs one by one in a loop, only saving the config and triggering the
>> KVM_REQ_PMU request. This approach does not immediately stop the event
>> before updating PMC.
>
> This is ture after KVM's 68fb4757e867 (v6.2). QEMU even supports v4.5
> (docs/system/target-i386.rst)... I'm not sure whether it is outdated,
> but it's better to mention the Linux version.
Thank you very much for the reminder.
I will:
1. Reorder the reasons and put the above at the end, because now "levels >=
KVM_PUT_RESET_STATE" and "exclude_host = 1" (Intel uses atomic MSR autoload
while looks AMD supports a special guest mode) are more convincing.
2. Add the commit id that you suggest to the last reason.
3. Add your Reviewed-by. Thank you very much!
Dongli Zhang
>
>> In additional, PMU MSRs are set only at levels >= KVM_PUT_RESET_STATE,
>> excluding runtime. Therefore, updating these MSRs without stopping events
>> should be acceptable.
>
> I agree.
>
>> Finally, KVM creates kernel perf events with host mode excluded
>> (exclude_host = 1). While the events remain active, they don't increment
>> the counter during QEMU vCPU userspace mode.
>>
>> No Fixed tag is going to be added for the commit 0d89436786b0 ("kvm:
>> migrate vPMU state"), because this isn't a bugfix.
>>
>> Signed-off-by: Dongli Zhang <dongli.zh...@oracle.com>
>> ---
>> target/i386/kvm/kvm.c | 9 ---------
>> 1 file changed, 9 deletions(-)
>
> Fine for me,
>
> Reviewed-by: Zhao Liu <zhao1....@intel.com>
>
