linux-kernel - Re: [PATCH 2/3] x86, perf: Support custom test values for extra

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Message-ID: <20150630111907.GF3644@twins.programming.kicks-ass.net>
Date:	Tue, 30 Jun 2015 13:19:07 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	eranian@...gle.com, linux-kernel@...r.kernel.org,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 2/3] x86, perf: Support custom test values for extra_regs

On Mon, Jun 29, 2015 at 02:22:14PM -0700, Andi Kleen wrote:
> From: Andi Kleen <ak@...ux.intel.com>
> 
> Current kernels always test extra registers at boot with RMW
> cycle, to catch lying virtual machines.
> 
> For a new register the standard 0x1ff test value does not work,
> as 0x1ff is not a valid value and causes an #GP.
> 
> Add the ability to add custom test values to an extra_reg
> into the description tables.

Just wondering; is there not a test value that works for all registers?
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