From: Will Deacon <will.deacon@arm.com>
Date: Thu, 28 Feb 2013 16:47:20 +0000 (+0100)
Subject: ARM: 7658/1: mm: fix race updating mm->context.id on ASID rollover
X-Git-Tag: v3.9-rc2~17^2~10
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=37f47e3d62533c931b04cb409f2eb299e6342331;p=pandora-kernel.git

ARM: 7658/1: mm: fix race updating mm->context.id on ASID rollover

If a thread triggers an ASID rollover, other threads of the same process
must be made to wait until the mm->context.id for the shared mm_struct
has been updated to new generation and associated book-keeping (e.g.
TLB invalidation) has ben performed.

However, there is a *tiny* window where both mm->context.id and the
relevant active_asids entry are updated to the new generation, but the
TLB flush has not been performed, which could allow another thread to
return to userspace with a dirty TLB, potentially leading to data
corruption. In reality this will never occur because one CPU would need
to perform a context-switch in the time it takes another to do a couple
of atomic test/set operations but we should plug the race anyway.

This patch moves the active_asids update until after the potential TLB
flush on context-switch.

Cc: <stable@vger.kernel.org> # 3.8
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
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