From: "Liang, Kan" <kan.liang@linux.intel.com>
To: "Wang, Wei W" <wei.w.wang@intel.com>,
"Li, Xiaoyao" <xiaoyao.li@intel.com>,
Peter Zijlstra <peterz@infradead.org>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@kernel.org>, Namhyung Kim <namhyung@kernel.org>,
"Christopherson,, Sean" <seanjc@google.com>,
Paolo Bonzini <pbonzini@redhat.com>,
"Liang, Kan" <kan.liang@intel.com>,
"Kleen, Andi" <andi.kleen@intel.com>
Cc: "linux-perf-users@vger.kernel.org"
<linux-perf-users@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>
Subject: Re: [RFC PATCH 0/2] KVM: VMX: Fix VM entry failure on PT_MODE_HOST_GUEST while host is using PT
Date: Thu, 15 Sep 2022 09:54:52 -0400 [thread overview]
Message-ID: <ef391316-cde5-3cda-ff0d-980e8ecc9aef@linux.intel.com> (raw)
In-Reply-To: <CY5PR11MB6365676799EBF86B3931D336DC499@CY5PR11MB6365.namprd11.prod.outlook.com>
On 2022-09-14 10:46 p.m., Wang, Wei W wrote:
> On Thursday, September 15, 2022 4:26 AM, Liang, Kan wrote:
>> The perf_event_disable() eventually invokes the intel_pt_stop().
>> We already expose the intel_pt_stop()/cpu_emergency_stop_pt() to other
>> modules. I don't think we have to use the perf_event_disable(). Also, the
>> perf_event_disable() requires extra codes.
>>
>> I went through the discussions. I agree with Sean's suggestion.
>> We should only put the logic in the KVM but all the MSR access details into the PT
>> driver.
>
> Even the driver itself doesn’t drive the save/restore of the MSRs, it is drived by perf.
It through perf_event, not driven by perf_event. The perf_event generic
code never knows when should invokes each driver to save/restore
information. It should be driven by the other subsystem e.g., scheduler.
For this case, KVM should drive the save/restore, and the PT driver
eventually does all the MSR access details.
> 1. If we make KVM a user of perf, we should do this via perf_event_disable/enable_*.
> 2. If we make KVM an alternative to perf (i.e. have direct control over PMU HW),
> we can do this via driver interfaces like perf.
> Per my experience, we should go for 1. Probably need Peter's opinions on this.
>
For 1, the perf_event_disable/enable_* are not enough. They don't
save/restore MSRs. If we go to this way, we have to introduce a new
generic interface to ask each driver to save/restore their MSRs when the
guest is entering/exiting. We'd better combine the new interface with
the existing perf_guest_get_msrs() of the core driver.
I think that's an ideal solution, but requires big changes in the code.
2 is the current KVM implementation. See pt_save_msr()/pt_load_msr(). I
don't think it's a right way. We'd better fix it.
The suggestion should be 3. The KVM notify the PT driver via the
interface provided by PT. The PT driver save/restore all the registers.
I think it's an acceptable solution with small code changes.
So I prefer 3.
Thanks,
Kan
>> But I prefer a more generic and straightforward function name, e.g.,
>> intel_pt_stop_save()/intel_pt_start_load(), in case other modules may want to
>> save/restore the PT information in their context switch later.
>>
>> Thanks,
>> Kan
>>
>>>
>>>> It seems perf_event_disable() is not used widely by other kernel
>>>> component.
>
> Because there are not lots of kernel users.
> You can check another user, watchdog_hld.c, perf_event_enable/disable are used there.
next prev parent reply other threads:[~2022-09-15 13:55 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-25 8:56 [RFC PATCH 0/2] KVM: VMX: Fix VM entry failure on PT_MODE_HOST_GUEST while host is using PT Xiaoyao Li
2022-08-25 8:56 ` [RFC PATCH 1/2] perf/x86/intel/pt: Introduce intel_pt_{stop,resume}() Xiaoyao Li
2022-08-25 15:23 ` Sean Christopherson
2022-08-25 8:56 ` [RFC PATCH 2/2] KVM: VMX: Stop/resume host PT before/after VM entry when PT_MODE_HOST_GUEST Xiaoyao Li
2022-08-25 15:34 ` Sean Christopherson
2022-08-25 15:45 ` Xiaoyao Li
2022-08-25 15:59 ` Sean Christopherson
2022-08-26 6:32 ` Xiaoyao Li
2022-08-26 15:08 ` Sean Christopherson
2022-08-29 7:49 ` [RFC PATCH 0/2] KVM: VMX: Fix VM entry failure on PT_MODE_HOST_GUEST while host is using PT Wang, Wei W
2022-08-29 17:33 ` Sean Christopherson
2022-08-30 6:02 ` Wang, Wei W
2022-09-08 7:25 ` Xiaoyao Li
2022-09-08 8:53 ` Wang, Wei W
2022-09-14 4:15 ` Xiaoyao Li
2022-09-14 6:16 ` Wang, Wei W
2022-09-14 20:25 ` Liang, Kan
2022-09-15 2:46 ` Wang, Wei W
2022-09-15 13:54 ` Liang, Kan [this message]
2022-09-15 14:39 ` Wang, Wei W
2022-09-15 15:42 ` Liang, Kan
2022-09-16 2:30 ` Wang, Wei W
2022-09-16 13:27 ` Liang, Kan
2022-09-19 13:46 ` Wang, Wei W
2022-09-19 14:41 ` Liang, Kan
2022-09-19 15:22 ` Wang, Wei W
2022-09-19 15:55 ` Liang, Kan
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