linux-kernel - Re: [PATCH RESEND] perf/x86/core: Completely disable guest PEBS via guest's global

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Message-ID: <Yw8NToJ5reQ+1rzt@hirez.programming.kicks-ass.net>
Date:   Wed, 31 Aug 2022 09:27:10 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Like Xu <like.xu.linux@...il.com>
Cc:     Sean Christopherson <seanjc@...gle.com>, kvm@...r.kernel.org,
        Kan Liang <kan.liang@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        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>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RESEND] perf/x86/core: Completely disable guest PEBS via
 guest's global_ctrl

On Wed, Aug 31, 2022 at 11:35:24AM +0800, Like Xu wrote:
> From: Like Xu <likexu@...cent.com>
> 
> When a guest PEBS counter is cross-mapped by a host counter, software
> will remove the corresponding bit in the arr[global_ctrl].guest and
> expect hardware to perform a change of state "from enable to disable"
> via the msr_slot[] switch during the vmx transaction.
> 
> The real world is that if user adjust the counter overflow value small
> enough, it still opens a tiny race window for the previously PEBS-enabled
> counter to write cross-mapped PEBS records into the guest's PEBS buffer,
> when arr[global_ctrl].guest has been prioritised (switch_msr_special stuff)
> to switch into the enabled state, while the arr[pebs_enable].guest has not.
> 
> Close this window by clearing invalid bits in the arr[global_ctrl].guest.
> 
> Cc: linux-perf-users@...r.kernel.org
> Cc: Kan Liang <kan.liang@...ux.intel.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Sean Christopherson <seanjc@...gle.com>
> Fixes: 854250329c02 ("KVM: x86/pmu: Disable guest PEBS temporarily in two rare situations")
> Signed-off-by: Like Xu <likexu@...cent.com>
> ---

Thanks!