linux-kernel - Re: [PATCH 1/2] perf: ignore LBR and offcore

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Date:	Wed, 18 Jun 2014 17:59:16 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Liang, Kan" <kan.liang@...el.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"Kleen, Andi" <andi.kleen@...el.com>
Subject: Re: [PATCH 1/2] perf: ignore LBR and offcore_rsp.

On Wed, Jun 18, 2014 at 03:52:55PM +0000, Liang, Kan wrote:
>     perf ignore LBR and offcore_rsp.
> 
>     x86, perf: Protect LBR and offcore rsp against KVM lying
> 
>     With -cpu host, KVM reports LBR and offcore support, if the host has support.
>     When the guest perf driver tries to access LBR or offcore_rsp MSR,
>     it #GPs all MSR accesses,since KVM doesn't handle LBR and offcore support.
>     So LBR and offcore rsp MSRs are needed to be protected by _safe().
> 
>     For reproducing the issue, please build the kernel with CONFIG_KVM_INTEL = y.
>     And CONFIG_PARAVIRT = n and CONFIG_KVM_GUEST = n.
>     Start the guest with -cpu host.
>     Run perf record with --branch-any or --branch-filter in guest to trigger LBR #GP.
>     Run perf stat offcore events (E.g. LLC-loads/LLC-load-misses ...) in guest to trigger offcore_rsp #GP
> 
>     Signed-off-by: Andi Kleen <ak@...ux.intel.com>

This order indicates Andi is the author; but there's no corresponding
From.

>     Signed-off-by: Kan Liang <kan.liang@...el.com>

And here I thought that Andi was of the opinion that if you set CPUID to
indicate a particular CPU you had better also handle all its MSRs.



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