linux-kernel - Re: [PATCH 1/3] Fix COW D-cache aliasing on fork

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Message-Id: <20061020.123635.95058911.davem@davemloft.net>
Date:	Fri, 20 Oct 2006 12:36:35 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	torvalds@...l.org
Cc:	nickpiggin@...oo.com.au, ralf@...ux-mips.org, akpm@...l.org,
	linux-kernel@...r.kernel.org, anemo@....ocn.ne.jp
Subject: Re: [PATCH 1/3] Fix COW D-cache aliasing on fork

From: Linus Torvalds <torvalds@...l.org>
Date: Fri, 20 Oct 2006 08:49:35 -0700 (PDT)

> Why not do the cache flush _after_ the TLB flush? There's still a mapping, 
> and never mind that it's read-only: the _mapping_ still exists, and I 
> doubt any CPU will not do the writeback (the readonly bit had better 
> affect the _frontend_ of the memory pipeline, but affectign the back end 
> would be insane and very hard, since you can't raise a fault any more).
> 
> Hmm?

You get an asynchronous fault from the L2 cache, and that's also what
happens when the TLB entry is missing during L2 writeback too.  You
get a level 15 non-maskable IRQ when these asynchronous errors happen.
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