linux-kernel - Re: [PATCH v2 3/6] x86, mm, asm-gen: Add ioremap

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]

Date:	Wed, 10 Sep 2014 13:08:38 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Toshi Kani <toshi.kani@...com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arnd Bergmann <arnd@...db.de>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Juergen Gross <jgross@...e.com>,
	Stefan Bader <stefan.bader@...onical.com>,
	Henrique de Moraes Holschuh <hmh@....eng.br>,
	Yigal Korman <yigal@...xistor.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: Re: [PATCH v2 3/6] x86, mm, asm-gen: Add ioremap_wt() for WT

On Wed, Sep 10, 2014 at 12:40 PM, Toshi Kani <toshi.kani@...com> wrote:
> On Wed, 2014-09-10 at 11:29 -0700, Andy Lutomirski wrote:
>> On Wed, Sep 10, 2014 at 9:51 AM, Toshi Kani <toshi.kani@...com> wrote:
>  :
>> > +#ifndef ARCH_HAS_IOREMAP_WT
>> > +#define ioremap_wt ioremap_nocache
>> > +#endif
>> > +
>>
>> This is a little bit sad.  I wouldn't be too surprised if there are
>> eventually users who prefer WC or WB over UC if WT isn't available
>> (and they'll want a corresponding way to figure out what kind of fence
>> to use).
>
> Right, this redirection is not ideal for the performance, but it is done
> this way for the correctness.  WT & UC have strongly ordered writes, but
> WB & WC do not.

Fair enough.  I think that this is unlikely to ever matter on x86, but
it might if NV-DIMMs end up used on another architecture w/o WT (or on
Xen, perhaps).  Your code is certainly fine from a correctness POV.

Aside: WB writes are IIRC even more strongly ordered than WC.

>
> Thanks,
> -Toshi
>



-- 
Andy Lutomirski
AMA Capital Management, LLC
--
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/