linux-kernel - Re: MTRR use in drivers

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: <b8bfa877-5663-4a93-94b4-6ea313e4d563@email.android.com>
Date:	Sun, 23 Jun 2013 07:07:46 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Brice Goglin <brice.goglin@...il.com>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	David Airlie <airlied@...ux.ie>,
	dri-devel@...ts.freedesktop.org
Subject: Re: MTRR use in drivers

Why do you care about performance when PAT is disabled?

Brice Goglin <brice.goglin@...il.com> wrote:

>Le 21/06/2013 07:00, H. Peter Anvin a écrit :
>> An awful lot of drivers, mostly DRI drivers, are still mucking with
>> MTRRs directly as opposed to using ioremap_wc() or similar
>interfaces.
>> In addition to the architecture dependency, this is really
>undesirable
>> because MTRRs are a limited resource, whereas page table attributes
>are not.
>>
>> Furthermore, this perpetuates the need for the horrific hack known as
>> "MTRR cleanup".
>>
>> What, if anything, can we do to clean up this mess?
>>
>> 	-hpa
>>
>
>The first network driver that used ioremap_wc() back in 2008 (myri10ge)
>had to keep using MTRR because ioremap_wc() silently falls back to
>ioremap_nocache() when PAT is disabled.
>
>I asked about this in https://lkml.org/lkml/2008/5/31/42 and there was
>some talk about putting the MTRR addition in the nocache fallback path
>but I guess nobody implemented the idea.
>
>Brice

-- 
Sent from my mobile phone. Please excuse brevity and lack of formatting.
--
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/