Commit 44734f23 authored by Aneesh Kumar K.V's avatar Aneesh Kumar K.V Committed by Michael Ellerman

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: 6a119eae ("powerpc/mm: Add a _PAGE_PTE bit")
Reported-by: default avatarHugh Dickins <hughd@google.com>
Suggested-by: default avatarHugh Dickins <hughd@google.com>
Signed-off-by: default avatarAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Acked-by: default avatarHugh Dickins <hughd@google.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent 68adb7bf
...@@ -158,9 +158,14 @@ static inline void pgd_set(pgd_t *pgdp, unsigned long val) ...@@ -158,9 +158,14 @@ static inline void pgd_set(pgd_t *pgdp, unsigned long val)
#define __swp_entry(type, offset) ((swp_entry_t) { \ #define __swp_entry(type, offset) ((swp_entry_t) { \
((type) << _PAGE_BIT_SWAP_TYPE) \ ((type) << _PAGE_BIT_SWAP_TYPE) \
| ((offset) << PTE_RPN_SHIFT) }) | ((offset) << PTE_RPN_SHIFT) })
/*
#define __pte_to_swp_entry(pte) ((swp_entry_t) { pte_val((pte)) }) * swp_entry_t must be independent of pte bits. We build a swp_entry_t from
#define __swp_entry_to_pte(x) __pte((x).val) * 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 #ifdef CONFIG_HAVE_ARCH_SOFT_DIRTY
#define _PAGE_SWP_SOFT_DIRTY (1UL << (SWP_TYPE_BITS + _PAGE_BIT_SWAP_TYPE)) #define _PAGE_SWP_SOFT_DIRTY (1UL << (SWP_TYPE_BITS + _PAGE_BIT_SWAP_TYPE))
......
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