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

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Message-ID: <20120821143115.GJ16230@one.firstfloor.org>
Date:	Tue, 21 Aug 2012 16:31:15 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	"Yan, Zheng" <zheng.z.yan@...el.com>
Cc:	a.p.zijlstra@...llo.nl, eranian@...gle.com, mingo@...e.hu,
	andi@...stfloor.org, 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.

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.

-Andi
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