linux-kernel - Re: [PATCH] disable CPU side GART accesses

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Date:	Thu, 16 Oct 2008 13:26:48 -0600
From:	Bob Montgomery <bob.montgomery@...com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"vojtech@...e.cz" <vojtech@...e.cz>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"chandru@...ibm.com" <chandru@...ibm.com>,
	Joerg Roedel <joerg.roedel@....com>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Pavel Machek <pavel@....cz>
Subject: Re: [PATCH] disable CPU side GART accesses

On Thu, 2008-10-16 at 17:43 +0000, Yinghai Lu wrote:
> On Thu, Oct 16, 2008 at 10:00 AM, Bob Montgomery <bob.montgomery@...com> wrote:
> >
> > The problem occurs when the copy operation reads from the GART aperture
> > (iommu window) and wakes up the GART translation hardware.  This patch
> > stops that by telling the GART to ignore addresses that come from the
> > CPU and to only translate addresses from the IO side.
> 
> why kdump need to copy those area? those area is supposed to be
> reserved in e820 table by BIOS or first kernel.
> 
> YH

The crashdump analysis tools do not need a copy of this area.  But if a
user tool associated with the kdump operation manages to touch it
through /proc/vmcore or /dev/oldmem, it can crash the kdump kernel.
This seemed like a simple and logical way to prevent that danger.

Bob Montgomery

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