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Message-ID: <20091219183305.GA10568@linux-mips.org>
Date: Sat, 19 Dec 2009 18:33:05 +0000
From: Ralf Baechle <ralf@...ux-mips.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Christoph Hellwig <hch@...radead.org>, tytso@....edu,
Kyle McMartin <kyle@...artin.ca>, linux-parisc@...r.kernel.org,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
James.Bottomley@...e.de, linux-arch@...r.kernel.org,
Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [git patches] xfs and block fixes for virtually indexed arches
On Thu, Dec 17, 2009 at 09:42:15AM -0800, Linus Torvalds wrote:
>
> I also think that the changes to bio_map_kernel() and bio_map_kern_endio()
> are not just "fundamentally ugly", I think they are made worse by the fact
> that it's not even done "right". You both flush the virtual caches before
> the IO and invalidate after - when the real pattern should be that you
> flush it before a write, and invalidate it after a read.
>
> And I really think that would be all much more properly done at the
> _caller_ level, not by the BIO layer.
>
> You must have some locking and allocation etc logic at the caller anyway,
> why doesn't _that_ level just do the flushing or invalidation?
And then there are certain types of caches that need invalidation before
_and_ after a DMA transaction as a workaround for a processor being
grossly abused in a system that it should not be used in. Basically the
issue is that falsly speculated stores may dirty caches.
Ralf
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