linux-kernel - Re: [PATCH] x86: use int instead of long to set reset vector back to 0

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Message-ID: <20110228151516.GA5662@srcf.ucam.org>
Date:	Mon, 28 Feb 2011 15:15:16 +0000
From:	Matthew Garrett <mjg@...hat.com>
To:	Don Zickus <dzickus@...hat.com>
Cc:	x86@...nel.org, LKML <linux-kernel@...r.kernel.org>,
	mingo@...hat.com
Subject: Re: [PATCH] x86: use int instead of long to set reset vector back
	to 0

On Mon, Feb 07, 2011 at 11:25:00PM -0500, Don Zickus wrote:
> A customer of ours, complained that when setting the reset vector
> back to 0, it trashed other data and hung their box.  They noticed
> when only 4 bytes were set to 0 instead of 8, everything worked
> correctly.

We're supposed to be resetting trampoline_phys_low and 
trampoline_phys_high here, which are two 16-bit values. Writing 64 bits 
is definitely going to overwrite space that we're not supposed to be 
touching.

> -	*((volatile long *)phys_to_virt(apic->trampoline_phys_low)) = 0;
> +	*((volatile int *)phys_to_virt(apic->trampoline_phys_low)) = 0;

I'd suggest either using u32 here, or alternatively make it more obvious 
what's going on and set trampoline_phys_low and trampoline_phys_high 
(which are both 16 bit) independently.

Ingo? Looks like you touched this last, but it seems that the bug was 
there already.
-- 
Matthew Garrett | mjg59@...f.ucam.org
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