linux-kernel - Re: [PATCH] perf/x86: Disable uncore on virtualized CPU.

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Date:	Tue, 21 Aug 2012 17:42:08 +0300
From:	Pekka Enberg <penberg@...nel.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	"Yan, Zheng" <zheng.z.yan@...el.com>, a.p.zijlstra@...llo.nl,
	eranian@...gle.com, mingo@...e.hu, avi@...hat.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf/x86: Disable uncore on virtualized CPU.

On Tue, Aug 21, 2012 at 05:08:37PM +0800, Yan, Zheng wrote:
>> From: "Yan, Zheng" <zheng.z.yan@...el.com>
>>
>> Initializing uncore PMU on virtualized CPU may hang the kernel.
>> This is because kvm does not emulate the entire hardware. Thers
>> are lots of uncore related MSRs, making kvm enumerate them all
>> is a non-trival task. So just disable uncore on virtualized CPU.

On Tue, Aug 21, 2012 at 5:31 PM, Andi Kleen <andi@...stfloor.org> wrote:
> I'm not sure cpu_has_hypervisor is reliable enough for this.
> Better find out why it hangs and fix that.
>
> Early rdmsrls should be rdmsrl_safe()
> Early writes in the driver should check if anything was written,
> and if not then disable itself.

It's unfortunate that the changelog does not include any reference to
the actual thread this was discussed in:

http://www.mail-archive.com/kvm@vger.kernel.org/msg77524.html
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