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	Tue, 19 Jul 2011 21:10:50 +1000 (EST)
Subject: Re: [RFC/PATCH] mm/futex: Fix futex writes on archs with SW
	tracking of dirty & young
From: Peter Zijlstra <peterz@infradead.org>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
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Date: Tue, 19 Jul 2011 13:10:24 +0200
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Cc: tony.luck@intel.com, Shan Hai <haishan.bai@gmail.com>,
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On Tue, 2011-07-19 at 14:29 +1000, Benjamin Herrenschmidt wrote:
> The futex code currently attempts to write to user memory within
> a pagefault disabled section, and if that fails, tries to fix it
> up using get_user_pages().
>=20
> This doesn't work on archs where the dirty and young bits are
> maintained by software, since they will gate access permission
> in the TLB, and will not be updated by gup().
>=20
> In addition, there's an expectation on some archs that a
> spurious write fault triggers a local TLB flush, and that is
> missing from the picture as well.
>=20
> I decided that adding those "features" to gup() would be too much
> for this already too complex function, and instead added a new
> simpler fixup_user_fault() which is essentially a wrapper around
> handle_mm_fault() which the futex code can call.
>=20
> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>=20

Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>