From: Sean Christopherson <seanjc@google.com>
To: Like Xu <like.xu.linux@gmail.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@kernel.org>, Namhyung Kim <namhyung@kernel.org>,
linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org,
kvm@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Ingo Molnar <mingo@redhat.com>
Subject: Re: [PATCH v2 7/7] KVM: VMX: Simplify capability check when handling PERF_CAPABILITIES write
Date: Thu, 4 Aug 2022 15:00:45 +0000 [thread overview]
Message-ID: <YuvfHZLGbU08S4ee@google.com> (raw)
In-Reply-To: <41e0b2a0-c53d-870f-d619-4008eb222d42@gmail.com>
On Thu, Aug 04, 2022, Like Xu wrote:
> On 4/8/2022 3:26 am, Sean Christopherson wrote:
> > Explicitly check for the absence of host support for LBRs or PEBS when
> > userspace attempts to enable said features by writing PERF_CAPABILITIES.
> > Comparing host support against the incoming value is unnecessary and
> > weird since the checks are buried inside an if-statement that verifies
> > userspace wants to enable the feature.
>
> If you mean this part in the KVM:
>
> case MSR_IA32_PERF_CAPABILITIES: {
> ...
> if (data & ~msr_ent.data)
> return 1;
> ...
>
> then this patch brings a flaw, for example:
>
> a user space can successfully set 0x1 on a host that reports a value of 0x5,
> which should not happen since the semantics of 0x1 and 0x5 for LBR_FMT
> may be completely different from the guest LBR driver's perspective.
/facepalm
I keep forgetting the caps need to match the host exactly. Thanks!
prev parent reply other threads:[~2022-08-04 15:00 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-03 19:26 [PATCH v2 0/7] KVM: x86: Intel PERF_CAPABILITIES fixes and cleanups Sean Christopherson
2022-08-03 19:26 ` [PATCH v2 1/7] KVM: x86: Refresh PMU after writes to MSR_IA32_PERF_CAPABILITIES Sean Christopherson
2022-08-03 19:26 ` [PATCH v2 2/7] perf/x86/core: Remove unnecessary stubs provided for KVM-only helpers Sean Christopherson
2022-08-04 8:49 ` Like Xu
2022-08-04 15:07 ` Sean Christopherson
2022-08-03 19:26 ` [PATCH v2 3/7] perf/x86/core: Drop the unnecessary return value from x86_perf_get_lbr() Sean Christopherson
2022-08-03 19:26 ` [PATCH v2 4/7] KVM: VMX: Advertise PMU LBRs if and only if perf supports LBRs Sean Christopherson
2022-08-03 19:26 ` [PATCH v2 5/7] KVM: VMX: Use proper type-safe functions for vCPU => LBRs helpers Sean Christopherson
2022-08-03 19:26 ` [PATCH v2 6/7] KVM: VMX: Adjust number of LBR records for PERF_CAPABILITIES at refresh Sean Christopherson
2022-08-03 19:26 ` [PATCH v2 7/7] KVM: VMX: Simplify capability check when handling PERF_CAPABILITIES write Sean Christopherson
2022-08-04 7:52 ` Like Xu
2022-08-04 15:00 ` Sean Christopherson [this message]
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