linux-kernel - Re: [PATCH] [ARM] force dcache flush if dcache

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Message-ID: <20091012170312.GB9453@flint.arm.linux.org.uk>
Date:	Mon, 12 Oct 2009 18:03:12 +0100
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	Hugh Dickins <hugh.dickins@...cali.co.uk>
Cc:	David Miller <davem@...emloft.net>,
	Nitin Gupta <ngupta@...are.org>, Nick Piggin <npiggin@...e.de>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH] [ARM] force dcache flush if dcache_dirty bit set

On Mon, Oct 12, 2009 at 05:09:53PM +0100, Hugh Dickins wrote:
> Sorry to muddy the waters on this, if you and Dave are sure that
> you have the right fix, down in your architectures, and that fix
> isn't going to hurt your performance significantly.

If I look at the issue from this point of view:

- we are using PG_arch_1 to delay cache handling for the page

- if PG_arch_1 is set on a page, we set it explicitly because we
  didn't do some flushing between the allocation of the page and
  mapping it into userspace

- if a page with PG_arch_1 set ever gets to userspace, this can
  only be because we did the lazy flushing thing

I don't see that there should have been any bearing on whether a page
has a mapping or not when we get to update_mmu_cache.  The issue here
is that > if PG_arch_1 is set on a page, then we didn't flush it at
the time when we believed it was appropriate to do so. <

Tell me I'm wrong (having only just sent it to Linus...)

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:
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