From 44734f23de2465c3c0d39e4a16df7735b23fd142 Mon Sep 17 00:00:00 2001 From: "Aneesh Kumar K.V" Date: Mon, 11 Jan 2016 21:19:34 +0530 Subject: 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 Suggested-by: Hugh Dickins Signed-off-by: Aneesh Kumar K.V Acked-by: Hugh Dickins Signed-off-by: Michael Ellerman diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h index 03c1a5a..8e040c4 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)) -- cgit v0.10.2