[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>

diff --git a/include/asm-powerpc/tlb.h b/include/asm-powerpc/tlb.h
index 0a17682663d8f308411b26e8ba28eb91e1c8fe96..66714042e4383399a597ec5867a14e46e52ee1bc 100644 (file)
--- a/include/asm-powerpc/tlb.h
+++ b/include/asm-powerpc/tlb.h
@@ -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();
 }