linux-kernel - MTRR initialization

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-next>] [day] [month] [year] [list]

Message-ID: <46EAB7DA.10507@symas.com>
Date:	Fri, 14 Sep 2007 09:33:30 -0700
From:	Howard Chu <hyc@...as.com>
To:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: MTRR initialization

Hi, was wondering if anyone else has been tripped up by this... I've got 4GB of 
RAM in my Asus A8V Deluxe and memory hole mapping enabled in the BIOS. By 
default, my system boots up with these MTRR settings:

reg00: base=0x00000000 (   0MB), size=4096MB: write-back, count=1
reg01: base=0x100000000 (4096MB), size=1024MB: write-back, count=1
reg02: base=0xc0000000 (3072MB), size=1024MB: uncachable, count=1
reg03: base=0xc0000000 (3072MB), size= 256MB: write-combining, count=1

The X server and various other programs try to add a mapping for my video 
card's buffer, at 0xd0000000, size=256MB, type=write-combining, and this always 
fails with a type mismatch error (old type is write-back). Apparently it's 
conflicting with mapping register 0. I can't just disable the existing settings 
and re-add them; the system hangs soon after disabling reg01.

I guess the kernel must be getting the initial setup from the BIOS. I've hacked 
around this in mtrr/generic.c by explicitly changing the MTRR state in 
get_mtrr_state to split the first mapping into two; one at base 0 size 2048M 
and one at base 2048M size 1024M. So now I have this, which is pretty much what 
I wanted:

reg00: base=0x00000000 (   0MB), size=2048MB: write-back, count=1
reg01: base=0x80000000 (2048MB), size=1024MB: write-back, count=1
reg02: base=0x100000000 (4096MB), size=1024MB: write-back, count=1
reg03: base=0xc0000000 (3072MB), size=1024MB: uncachable, count=1
reg04: base=0xc0000000 (3072MB), size= 256MB: write-combining, count=1
reg05: base=0xd0000000 (3328MB), size= 256MB: write-combining, count=1

So the question is - was there an easier/correct way to do this?

It might have been nice if the MTRR ioctls allowed the register number to be 
specified on the Set commands, though I'm not sure that would have helped in 
this case.
-- 
   -- Howard Chu
   Chief Architect, Symas Corp.  http://www.symas.com
   Director, Highland Sun        http://highlandsun.com/hyc/
   Chief Architect, OpenLDAP     http://www.openldap.org/project/
-
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/