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authorAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>2016-01-11 21:19:34 +0530
committerMichael Ellerman <mpe@ellerman.id.au>2016-01-12 11:02:35 +1100
commit44734f23de2465c3c0d39e4a16df7735b23fd142 (patch)
tree9437405c5fff14e2820c0359367386686af80b69 /arch
parent68adb7bfd66504e97364651fb7dac3f9c8aa8561 (diff)
downloadlinux-44734f23de2465c3c0d39e4a16df7735b23fd142.tar.gz
powerpc/mm: Fix _PAGE_PTE breaking swapoff
Core kernel expects swp_entry_t to consist of only swap type and swap offset. We should not leak pte bits into swp_entry_t. This breaks swapoff which use the swap type and offset to build a swp_entry_t and later compare that to the swp_entry_t obtained from linux page table pte. Leaking pte bits into swp_entry_t breaks that comparison and results in us looping in try_to_unuse. The stack trace can be anywhere below try_to_unuse() in mm/swapfile.c, since swapoff is circling around and around that function, reading from each used swap block into a page, then trying to find where that page belongs, looking at every non-file pte of every mm that ever swapped. Fixes: 6a119eae942c ("powerpc/mm: Add a _PAGE_PTE bit") Reported-by: Hugh Dickins <hughd@google.com> Suggested-by: Hugh Dickins <hughd@google.com> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com> Acked-by: Hugh Dickins <hughd@google.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Diffstat (limited to 'arch')
-rw-r--r--arch/powerpc/include/asm/book3s/64/pgtable.h11
1 files changed, 8 insertions, 3 deletions
diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
index 03c1a5a21c0c..8e040c42e931 100644
--- a/arch/powerpc/include/asm/book3s/64/pgtable.h
+++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
@@ -158,9 +158,14 @@ static inline void pgd_set(pgd_t *pgdp, unsigned long val)
#define __swp_entry(type, offset) ((swp_entry_t) { \
((type) << _PAGE_BIT_SWAP_TYPE) \
| ((offset) << PTE_RPN_SHIFT) })
-
-#define __pte_to_swp_entry(pte) ((swp_entry_t) { pte_val((pte)) })
-#define __swp_entry_to_pte(x) __pte((x).val)
+/*
+ * swp_entry_t must be independent of pte bits. We build a swp_entry_t from
+ * swap type and offset we get from swap and convert that to pte to find a
+ * matching pte in linux page table.
+ * Clear bits not found in swap entries here.
+ */
+#define __pte_to_swp_entry(pte) ((swp_entry_t) { pte_val((pte)) & ~_PAGE_PTE })
+#define __swp_entry_to_pte(x) __pte((x).val | _PAGE_PTE)
#ifdef CONFIG_HAVE_ARCH_SOFT_DIRTY
#define _PAGE_SWP_SOFT_DIRTY (1UL << (SWP_TYPE_BITS + _PAGE_BIT_SWAP_TYPE))