linux-kernel - Re: [PATCH 1/1] x86: Exclude E820_RESERVED regions and memory holes above 4 GB from direct mapping.

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1319148647.13035.4.camel@jshin-Toonie>
Date:	Thu, 20 Oct 2011 17:10:47 -0500
From:	Jacob Shin <jacob.shin@....com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Andi Kleen <andi@...stfloor.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Yinghai Lu <yinghai.lu@...cle.com>,
	"Herrmann3, Andreas" <Andreas.Herrmann3@....com>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] x86: Exclude E820_RESERVED regions and memory holes
 above 4 GB from direct mapping.

On Thu, 2011-10-20 at 16:30 -0500, H. Peter Anvin wrote:
> On 10/20/2011 02:28 PM, Andi Kleen wrote:
> > Jacob Shin <jacob.shin@....com> writes:
> > 
> >> On systems with very large memory (1 TB in our case), BIOS may report a
> >> reserved region or a hole in the E820 map, even above the 4 GB range. Exclude
> >> these from the direct mapping.
> > 
> > This doesn't make much sense.  Holes above 4GB are completely legal.
> > 
> > If you need to workaround a specific broken BIOS you would need a quirk
> > only matching that system, with a suitable "BIOS is broken" message.
> > 
> 
> The problem is that apparently right now we map those unconditionally
> into the 1:1 map and mark them cacheable in PAT, which we *don't* for
> the < 4 GiB map.
> 
> This thus makes the behavior match < 4 GiB, which is the correct
> behavior; this should be made clear in the patch description.

Will something like:

"On systems with very large memory (1 TB in our case), BIOS may report a
reserved region or a hole in the E820 map, even above the 4 GB range.
Avoid mapping them unconditionally into kernel 1:1 direct mapping as
cacheable memory, as we also already do for the MMIO hole under 4 GB."

Work?

Otherwise, does the patch look acceptable?

Thanks!

-Jacob Shin
Advanced Micro Devices, Inc.

> 
> 	-hpa
> 



--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/