linux-kernel - Re: [PATCH] trim memory not covered by WB MTRRs

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: <200706071035.18356.jesse.barnes@intel.com>
Date:	Thu, 7 Jun 2007 10:35:18 -0700
From:	Jesse Barnes <jesse.barnes@...el.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	linux-kernel@...r.kernel.org,
	Justin Piszcz <jpiszcz@...idpixels.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH] trim memory not covered by WB MTRRs

On Thursday, June 7, 2007 1:16 am Andi Kleen wrote:
> On Wed, Jun 06, 2007 at 12:29:23PM -0700, Jesse Barnes wrote:
> > On some machines, buggy BIOSes don't properly setup WB MTRRs to
> > cover all available RAM, meaning the last few megs (or even gigs)
> > of memory will be marked uncached.  Since Linux tends to allocate
> > from high memory addresses first, this causes the machine to be
> > unusably slow as soon as the kernel starts really using memory
> > (i.e. right around init time).
>
> In theory -- while not recommended -- a BIOS could also
> use a default fallback MTRR for cached and use explicit MTRRs to
> map the non existing ranges uncached. Would it make sense to handle
> this case?

Probably.  I could just check the default memory type and bail out if 
it's cacheable.

> Should also probably have some command line option
> to disable the check in case something bad happens with it.

Sure.

> Another thing that might be sense to investigate in relationship
> to this patch is large page mappings with MTRRs. iirc P4 and also K8
> splits pages internally with MTRR boundaries and might have some
> other bad side effects. Should we use this as hints to use 4K pages
> for the boundary areas?

Or I could trim to the nearest large page boundary...  We'd lose a 
little more memory but it would keep things simple.

Jesse
-
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/