From: Juergen Gross <jgross@suse.com>
To: Jiri Kosina <jikos@kernel.org>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Michal Hocko <mhocko@suse.com>
Subject: Re: Access to non-RAM pages
Date: Sat, 1 Sep 2018 12:47:48 +0200 [thread overview]
Message-ID: <b1b5ef64-d49b-e3f7-98b4-0ae3fd57b812@suse.com> (raw)
In-Reply-To: <alpine.LRH.2.00.1808312312480.14475@gjva.wvxbf.pm>
On 31/08/18 23:18, Jiri Kosina wrote:
> On Wed, 29 Aug 2018, Juergen Gross wrote:
>
>> While being very unlikely I still believe this is possible. Any
>> thoughts?
>
> So in theory we should somehow test whether the next page is some form of
> mmio/gart/... mapping, but I guess that by itself would kill the
> performance advantage of the whole load_unaligned_zeropad() trick.
>
> And yes, the sideffects of reading from mmio mapping is a real thing --
> see for example the issue fixed by 2a3e83c6f9.
>
> If noone has any clever idea how to work this around (I don't), I am
> afraid we'd have to ditch the whole DCACHE_WORD_ACCESS optimization, as
> it's silently dangerous.
Are there any architectures which can still use DCACHE_WORD_ACCESS?
x86 shouldn't, what about powerpc, arm and arm64?
I'm happy to send patches to remove selection of DCACHE_WORD_ACCESS
and eventually to remove all of the load_unaligned_zeropad() stuff.
Juergen
next prev parent reply other threads:[~2018-09-01 10:47 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-29 12:10 Juergen Gross
2018-08-31 21:18 ` Jiri Kosina
2018-09-01 10:47 ` Juergen Gross [this message]
2018-09-01 17:13 ` Al Viro
2018-09-01 21:48 ` Jiri Kosina
2018-09-01 17:27 ` Linus Torvalds
2018-09-01 18:06 ` Linus Torvalds
2018-09-03 0:48 ` Benjamin Herrenschmidt
2018-09-03 0:55 ` Benjamin Herrenschmidt
2018-09-03 1:38 ` Linus Torvalds
2018-09-03 1:42 ` Linus Torvalds
2018-09-03 2:00 ` Benjamin Herrenschmidt
2018-09-03 2:10 ` Linus Torvalds
2018-09-03 2:25 ` Benjamin Herrenschmidt
2018-09-03 2:47 ` Linus Torvalds
2018-09-03 2:52 ` Linus Torvalds
2018-09-03 3:44 ` Benjamin Herrenschmidt
2018-09-03 5:08 ` Juergen Gross
2018-09-03 6:05 ` Jiri Kosina
2018-09-03 10:36 ` Will Deacon
2018-09-03 1:44 ` Benjamin Herrenschmidt
2018-09-03 1:46 ` Benjamin Herrenschmidt
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