Commit 6ad8d010 authored May 27, 2007 by Benjamin Herrenschmidt Committed by Paul Mackerras Jun 02, 2007

[POWERPC] Fix possible access to free pages



I think we have a subtle race on ppc64 with the tlb batching.  The
common code expects tlb_flush() to actually flush any pending TLB
batch.  It does that because it delays all page freeing until after
tlb_flush() is called, in order to ensure no stale reference to
those pages exist in any TLB, thus causing potential access to
the freed pages.

However, our tlb_flush only triggers the RCU for freeing page
table pages, it does not currently trigger a flush of a pending
TLB/hash batch, which is, I think, an error.  This fixes it.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

parent 988519ac

include/asm-powerpc/tlb.h

+9 −0

Original line number	Diff line number	Diff line
		@@ -38,6 +38,15 @@ extern void pte_free_finish(void);

		static inline void tlb_flush(struct mmu_gather *tlb)
		{
		struct ppc64_tlb_batch *tlbbatch = &__get_cpu_var(ppc64_tlb_batch);

		/* If there's a TLB batch pending, then we must flush it because the
		* pages are going to be freed and we really don't want to have a CPU
		* access a freed page because it has a stale TLB
		*/
		if (tlbbatch->index)
		__flush_tlb_pending(tlbbatch);

		pte_free_finish();
		}