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

[Ralf Baechle <ralf@linux-mips.org>]

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