linux-kernel - Re: [git patches] xfs and block fixes for virtually indexed arches

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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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