linux-kernel - Re: [PATCH] x86: Fix AMD K6 indirect call check v2

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Message-ID: <51741CB2.3090209@zytor.com>
Date:	Sun, 21 Apr 2013 10:06:58 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	x86@...nel.org, linux-kernel@...r.kernel.org,
	Andi Kleen <ak@...ux.intel.com>, Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH] x86: Fix AMD K6 indirect call check v2

On 04/21/2013 09:49 AM, Andi Kleen wrote:
> From: Andi Kleen <ak@...ux.intel.com>
> 
> The AMD K6 errata check relies on timing a indirect call.
> But the way it was written it could be optimized to a direct call.
> Force gcc to actually do a indirect call and not just
> constant resolve the target address.
> 
> Found during code review, no runtime testing due to lack
> of hardware.

Maybe it would be even better to just code the indirect call instruction
in assembly?

Something like:

	asm volatile("call *%0"
		     : : "r" (vide)
		     : "eax", "ecx", "edx");

Gotta love the metal mask(?) fix without bumping the stepping number...

	-hpa

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