linux-kernel - Re: fuse, get_user_pages, flush_anon_page, aliasing caches and all that again

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Message-Id: <E1H0wiB-0003iu-00@dorka.pomaz.szeredi.hu>
Date:	Sun, 31 Dec 2006 10:10:35 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	davem@...emloft.net
CC:	rmk+lkml@....linux.org.uk, torvalds@...l.org,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	akpm@...l.org
Subject: Re: fuse, get_user_pages, flush_anon_page, aliasing caches and all
 that again

> Therefore, FUSE probably could have been fixed by judicious use
> of copy_{to,from}_user_page() calls instead of adding this new
> ad-hoc flush_anon_page() thing.

Probably, but I don't think either interface is perfect.
copy_*_user_page() will double flush the user mapping
(get_user_pages() already does a flush_dcache_page()).  Actually
nothing except ptrace uses the copy_*_user_page() interface even
though there are many uses of get_user_pages().

What I think get_user_pages() really needs is a single operation that

  - flushes the virtual address view
  - flushes the kernel view

regardles whether the page is anonymous or file backed.

Miklos
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