linux-kernel - Re: pgprot_writecombine() and PATs on x86

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: <m11wi8s36o.fsf@ebiederm.dsl.xmission.com>
Date:	Wed, 25 Apr 2007 12:45:51 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Roland Dreier <rdreier@...co.com>
Cc:	Andi Kleen <ak@...e.de>, linux-kernel@...r.kernel.org,
	mst@...lanox.co.il, jackm@...lanox.co.il
Subject: Re: pgprot_writecombine() and PATs on x86

Roland Dreier <rdreier@...co.com> writes:

>  > Roland is the mlx4 sane enough to put the memory that needs
>  > write-combining a prefetchable bar.  So several cards can be combined
>  > together?
>
> Yes, it is in a prefetchable BAR.  It's the second half of the second
> BAR in:
>
>     0d:00.0 InfiniBand: Mellanox Technologies Unknown device 634a (rev a0)
>             Subsystem: Mellanox Technologies Unknown device 634a
>             Flags: bus master, fast devsel, latency 0, IRQ 16
>             Memory at fc400000 (64-bit, non-prefetchable) [size=1M]
>             Memory at d8000000 (64-bit, prefetchable) [size=8M]
>             Memory at fc3fe000 (64-bit, non-prefetchable) [size=8K]
>             Capabilities: <access denied>
>
> but I'm not sure what you mean about combining several cards?

So in general the pci prefetchable attribute means write-combining as
well as prefetching is safe.  A sane BIOS will allocate prefetchable
BARS contiguously in the address space.  So on a good day you
can just use one MTRR to map all of the prefetchable BARs as write-combining.

Eric
-
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/