linux-kernel - Re: [PATCH RFC v2 00/17] KVM: x86/pmu: Add support to enable Guest PEBS via DS

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Message-ID: <20201110151257.GP2611@hirez.programming.kicks-ass.net>
Date:   Tue, 10 Nov 2020 16:12:57 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Like Xu <like.xu@...ux.intel.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Kan Liang <kan.liang@...ux.intel.com>, luwei.kang@...el.com,
        Thomas Gleixner <tglx@...utronix.de>, wei.w.wang@...el.com,
        Tony Luck <tony.luck@...el.com>,
        Stephane Eranian <eranian@...gle.com>,
        Mark Gross <mgross@...ux.intel.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC v2 00/17] KVM: x86/pmu: Add support to enable Guest
 PEBS via DS

On Mon, Nov 09, 2020 at 10:12:37AM +0800, Like Xu wrote:
> The Precise Event Based Sampling(PEBS) supported on Intel Ice Lake server
> platforms can provide an architectural state of the instruction executed
> after the instruction that caused the event. This patch set enables the
> the PEBS via DS feature for KVM (also non) Linux guest on the Ice Lake.
> The Linux guest can use PEBS feature like native:
> 
>   # perf record -e instructions:ppp ./br_instr a
>   # perf record -c 100000 -e instructions:pp ./br_instr a
> 
> If the counter_freezing is not enabled on the host, the guest PEBS will
> be disabled on purpose when host is using PEBS facility. By default,
> KVM disables the co-existence of guest PEBS and host PEBS.

Uuhh, what?!? counter_freezing should never be enabled, its broken. Let
me go delete all that code.