linux-kernel - Re: [PATCH RFC 2/2] KVM: x86/vPMU: ignore access to LBR-related MSRs

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Message-ID: <20171206155728.GL3070@tassilo.jf.intel.com>
Date:   Wed, 6 Dec 2017 07:57:28 -0800
From:   Andi Kleen <ak@...ux.intel.com>
To:     Jan Dakinevich <jan.dakinevich@...tuozzo.com>
Cc:     linux-kernel@...r.kernel.org,
        "Denis V . Lunev" <den@...tuozzo.com>,
        Roman Kagan <rkagan@...tuozzo.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Kan Liang <kan.liang@...el.com>,
        Stephane Eranian <eranian@...gle.com>,
        Colin King <colin.king@...onical.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Jin Yao <yao.jin@...ux.intel.com>, kvm@...r.kernel.org
Subject: Re: [PATCH RFC 2/2] KVM: x86/vPMU: ignore access to LBR-related MSRs


If you do all this it's only a small step to fully enable LBRs for guests. 

Just need to allow them to be written, expose PERF_CAPABILITIES too, and
start/stop them on entry/exit, and enable context switching through perf in
the host.

That would be far better than creating a frankenstate where LBR is there but
mostly broken on some KVM versions.

-Andi