Commit 17ebba1f authored Jun 07, 2010 by Nicolas Pitre Committed by Russell King Jun 08, 2010

ARM: 6165/1: trap overflows on highmem pages from kmap_atomic when debugging



When CONFIG_DEBUG_HIGHMEM is used, the fixmap entry used for a highmem page
by kmap_atomic() is always cleared by kunmap_atomic().  This helps find
bad usages such as dereferences after the unmap, or overflow into the
adjacent fixmap areas.

But this debugging aid is completely bypassed when a kmap for the same
page already exists as the kmap is reused instead.  ON VIVT systems we
have no choice but to reuse that kmap due to cache coherency issues,
but on non VIVT systems we should always force the fixmap usage when
debugging is active.

Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

parent b394eebd

arch/arm/mm/highmem.c

+10 −1

Original line number	Diff line number	Diff line
		@@ -48,6 +48,15 @@ void kmap_atomic(struct page page, enum km_type type)

		debug_kmap_atomic(type);

		#ifdef CONFIG_DEBUG_HIGHMEM
		/*
		* There is no cache coherency issue when non VIVT, so force the
		* dedicated kmap usage for better debugging purposes in that case.
		*/
		if (!cache_is_vivt())
		kmap = NULL;
		else
		#endif
		kmap = kmap_high_get(page);
		if (kmap)
		return kmap;

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