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

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Message-Id: <20061231.014630.130845911.davem@davemloft.net>
Date:	Sun, 31 Dec 2006 01:46:30 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	rmk+lkml@....linux.org.uk
Cc:	torvalds@...l.org, miklos@...redi.hu, 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

From: Russell King <rmk+lkml@....linux.org.uk>
Date: Sun, 31 Dec 2006 09:23:18 +0000

> We do this on ARM - if page_mapping() is NULL, we flush the kernel
> alias unconditionally.  However, we have no view where the user
> mapping of that page is, which is where the problem is.  Cache lines
> remain allocated for the user mapping and data contained within is
> not visible via the kernel mapping.

You can walk the RMAP list.

> However, it's not only FUSE which is suffering - direct-IO also doesn't
> work.  If my analysis is correct, only _two_ users of get_user_pages()
> with the current process actually does the right thing and that's ptrace
> and ELF core dumping.  All other users are buggy.

I do not argue that these cases need work, in fact I am aware
of the direct-IO bit.
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