linux-kernel - Re: Uncool feature for TTM introduced by x86, pat: Use page flags to track memtypes of RAM pages

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:	Thu, 18 Feb 2010 09:38:01 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Jerome Glisse <glisse@...edesktop.org>, suresh.b.siddha@...el.com,
	venkatesh.pallipadi@...el.com, thellstrom@...are.com,
	airlied@...ux.ie, currojerez@...eup.net,
	linux-kernel@...r.kernel.org
Subject: Re: Uncool feature for TTM introduced by x86, pat: Use page flags
 to track memtypes of RAM pages

On 02/18/2010 09:27 AM, Andi Kleen wrote:
> Jerome Glisse <glisse@...edesktop.org> writes:
>>
>> Can we modify the interface to support again changing from uc to wc
>> or wc to uc ? (i can try to do a patch for that).
> 
> At least on Intel CPUs that support self-snoop (all modern
> ones) that should really be very cheap.
> 

The UC/WC transition should be particularly trivial; I don't see any
reason it should have to go through any other procedure on *any* CPU --
selfsnoop shouldn't even figure into it, since neither UC nor WC
actually caches anything.  For the WC->UC direction, all we should need
to do is to flush the write combiners; a simple wmb() will do that.

Self-snoop is about not having to flush something that can have been
cached, as is normally needed to do WB/WT/WP -> UC/WC.

	-hpa

--
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/