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Date: Wed, 6 Dec 2017 07:57:28 -0800
From: Andi Kleen <ak@linux.intel.com>
To: Jan Dakinevich <jan.dakinevich@virtuozzo.com>
Cc: linux-kernel@vger.kernel.org, "Denis V . Lunev" <den@virtuozzo.com>,
        Roman Kagan <rkagan@virtuozzo.com>,
        Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>,
        x86@kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
        Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        Kan Liang <kan.liang@intel.com>, Stephane Eranian <eranian@google.com>,
        Colin King <colin.king@canonical.com>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Jin Yao <yao.jin@linux.intel.com>, kvm@vger.kernel.org
Subject: Re: [PATCH RFC 2/2] KVM: x86/vPMU: ignore access to LBR-related MSRs
Message-ID: <20171206155728.GL3070@tassilo.jf.intel.com>
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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