linux-kernel - Re: [PATCH v4 10/38] perf/x86: Support switch_guest

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Message-ID: <dacd4a8e-5104-4043-b647-63e2df6d6a94@linux.intel.com>
Date: Fri, 25 Apr 2025 09:56:16 -0400
From: "Liang, Kan" <kan.liang@...ux.intel.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Mingwei Zhang <mizhang@...gle.com>, Ingo Molnar <mingo@...hat.com>,
 Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>, Sean Christopherson <seanjc@...gle.com>,
 Paolo Bonzini <pbonzini@...hat.com>, Mark Rutland <mark.rutland@....com>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
 Adrian Hunter <adrian.hunter@...el.com>, Liang@...gle.com,
 "H. Peter Anvin" <hpa@...or.com>, linux-perf-users@...r.kernel.org,
 linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
 linux-kselftest@...r.kernel.org, Yongwei Ma <yongwei.ma@...el.com>,
 Xiong Zhang <xiong.y.zhang@...ux.intel.com>,
 Dapeng Mi <dapeng1.mi@...ux.intel.com>, Jim Mattson <jmattson@...gle.com>,
 Sandipan Das <sandipan.das@....com>, Zide Chen <zide.chen@...el.com>,
 Eranian Stephane <eranian@...gle.com>, Shukla Manali
 <Manali.Shukla@....com>, Nikunj Dadhania <nikunj.dadhania@....com>
Subject: Re: [PATCH v4 10/38] perf/x86: Support switch_guest_ctx interface

On 2025-04-25 9:43 a.m., Peter Zijlstra wrote:
> On Fri, Apr 25, 2025 at 09:06:26AM -0400, Liang, Kan wrote:
>>
>>
>> On 2025-04-25 7:15 a.m., Peter Zijlstra wrote:
>>> On Mon, Mar 24, 2025 at 05:30:50PM +0000, Mingwei Zhang wrote:
>>>> From: Kan Liang <kan.liang@...ux.intel.com>
>>>>
>>>> Implement switch_guest_ctx interface for x86 PMU, switch PMI to dedicated
>>>> KVM_GUEST_PMI_VECTOR at perf guest enter, and switch PMI back to
>>>> NMI at perf guest exit.
>>>>
>>>> Signed-off-by: Xiong Zhang <xiong.y.zhang@...ux.intel.com>
>>>> Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
>>>> Tested-by: Yongwei Ma <yongwei.ma@...el.com>
>>>> Signed-off-by: Mingwei Zhang <mizhang@...gle.com>
>>>> ---
>>>>  arch/x86/events/core.c | 12 ++++++++++++
>>>>  1 file changed, 12 insertions(+)
>>>>
>>>> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
>>>> index 8f218ac0d445..28161d6ff26d 100644
>>>> --- a/arch/x86/events/core.c
>>>> +++ b/arch/x86/events/core.c
>>>> @@ -2677,6 +2677,16 @@ static bool x86_pmu_filter(struct pmu *pmu, int cpu)
>>>>  	return ret;
>>>>  }
>>>>  
>>>> +static void x86_pmu_switch_guest_ctx(bool enter, void *data)
>>>> +{
>>>> +	u32 guest_lvtpc = *(u32 *)data;
>>>> +
>>>> +	if (enter)
>>>> +		apic_write(APIC_LVTPC, guest_lvtpc);
>>>> +	else
>>>> +		apic_write(APIC_LVTPC, APIC_DM_NMI);
>>>> +}
>>>
>>> This, why can't it use x86_pmu.guest_lvtpc here and call it a day? Why
>>> is that argument passed around through the generic code only to get back
>>> here?
>>
>> The vector has to be from the KVM. However, the current interfaces only
>> support KVM read perf variables, e.g., perf_get_x86_pmu_capability and
>> perf_get_hw_event_config.
>> We need to add an new interface to allow the KVM write a perf variable,
>> e.g., perf_set_guest_lvtpc.
> 
> But all that should remain in x86, there is no reason what so ever to
> leak this into generic code.
> 

Sure. I will change it in the V5.

Thanks,
Kan