linux-kernel - Re: [PATCH 0/3] KVM: x86: Fix Intel PT Host/Guest mode when host tracing also

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Message-ID: <Zt/g9Cpix06Ccg4z@debian-scheme>
Date: Tue, 10 Sep 2024 14:02:28 +0800
From: Zhenyu Wang <zhenyuw@...ux.intel.com>
To: Adrian Hunter <adrian.hunter@...el.com>
Cc: Sean Christopherson <seanjc@...gle.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Zhenyu Wang <zhenyuw@...ux.intel.com>, kvm@...r.kernel.org,
	Shuah Khan <shuah@...nel.org>, linux-kselftest@...r.kernel.org,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	H Peter Anvin <hpa@...or.com>, Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Jiri Olsa <jolsa@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
	Ian Rogers <irogers@...gle.com>,
	Kan Liang <kan.liang@...ux.intel.com>, linux-kernel@...r.kernel.org,
	linux-perf-users@...r.kernel.org,
	Mingwei Zhang <mizhang@...gle.com>
Subject: Re: [PATCH 0/3] KVM: x86: Fix Intel PT Host/Guest mode when host
 tracing also


Add Mingwei.

On 2024.09.06 16:00:23 +0300, Adrian Hunter wrote:
> Hi
> 
> There is a long-standing problem whereby running Intel PT on host and guest
> in Host/Guest mode, causes VM-Entry failure.
> 
> The motivation for this patch set is to provide a fix for stable kernels
> prior to the advent of the "Mediated Passthrough vPMU" patch set:
> 
> 	https://lore.kernel.org/kvm/20240801045907.4010984-1-mizhang@google.com/
> 
> which would render a large part of the fix unnecessary but likely not be
> suitable for backport to stable due to its size and complexity.
> 
> Ideally, this patch set would be applied before "Mediated Passthrough vPMU"
> 
> Note that the fix does not conflict with "Mediated Passthrough vPMU", it
> is just that "Mediated Passthrough vPMU" will make the code to stop and
> restart Intel PT unnecessary.
>

With mediated passthrough vPMU, we could enable PT pmu's PERF_PMU_CAP_PASSTHROUGH_VPMU
capability like core pmu, then perf guest helper could handle any host PT events
during VM entry/exit as well like core perf events. The benefit is general perf interface
to handle like others. But it would be sure to depend on passthrough vPMU be enabled,
not as this to fix in case w/o that.

I have local patches to work against passthrough vPMU, but like passthrough vPMU
to be settled down first. With Adrian's change, it could be also possible to decouple
the dependency, so may support in both cases with or w/o passthrough vPMU enabled. 

> 
> Adrian Hunter (3):
>       KVM: x86: Fix Intel PT IA32_RTIT_CTL MSR validation
>       KVM: x86: Fix Intel PT Host/Guest mode when host tracing also
>       KVM: selftests: Add guest Intel PT test
> 
>  arch/x86/events/intel/pt.c                         | 131 ++++++-
>  arch/x86/events/intel/pt.h                         |  10 +
>  arch/x86/include/asm/intel_pt.h                    |   4 +
>  arch/x86/kvm/vmx/vmx.c                             |  26 +-
>  arch/x86/kvm/vmx/vmx.h                             |   1 -
>  tools/testing/selftests/kvm/Makefile               |   1 +
>  .../selftests/kvm/include/x86_64/processor.h       |   1 +
>  tools/testing/selftests/kvm/x86_64/intel_pt.c      | 381 +++++++++++++++++++++
>  8 files changed, 532 insertions(+), 23 deletions(-)
>  create mode 100644 tools/testing/selftests/kvm/x86_64/intel_pt.c
> 
> base-commit: d45aab436cf06544abeeffc607110f559a3af3b4
> 
> 
> Regards
> Adrian
> 

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