Andy Lutomirski reported that in case if a page with _PAGE_SOFT_DIRTY bit set get swapped out, the bit is getting lost and no longer available when pte read back.
To resolve this we introduce _PTE_SWP_SOFT_DIRTY bit which is saved in pte entry for the page being swapped out. When such page is to be read back from a swap cache we check for bit presence and if it's there we clear it and restore the former _PAGE_SOFT_DIRTY bit back. One of the problem was to find a place in pte entry where we can save the _PTE_SWP_SOFT_DIRTY bit while page is in swap. The _PAGE_PSE was chosen for that, it doesn't intersect with swap entry format stored in pte. Reported-by: Andy Lutomirski <[email protected]> Signed-off-by: Cyrill Gorcunov <[email protected]> Cc: Pavel Emelyanov <[email protected]> Cc: Andrew Morton <[email protected]> Cc: Matt Mackall <[email protected]> Cc: Xiao Guangrong <[email protected]> Cc: Marcelo Tosatti <[email protected]> Cc: KOSAKI Motohiro <[email protected]> Cc: Stephen Rothwell <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: "Aneesh Kumar K.V" <[email protected]> --- arch/x86/include/asm/pgtable.h | 15 +++++++++++++++ arch/x86/include/asm/pgtable_types.h | 13 +++++++++++++ fs/proc/task_mmu.c | 21 +++++++++++++++------ include/asm-generic/pgtable.h | 15 +++++++++++++++ include/linux/swapops.h | 2 ++ mm/memory.c | 2 ++ mm/rmap.c | 6 +++++- mm/swapfile.c | 19 +++++++++++++++++-- 8 files changed, 84 insertions(+), 9 deletions(-) Index: linux-2.6.git/arch/x86/include/asm/pgtable.h =================================================================== --- linux-2.6.git.orig/arch/x86/include/asm/pgtable.h +++ linux-2.6.git/arch/x86/include/asm/pgtable.h @@ -314,6 +314,21 @@ static inline pmd_t pmd_mksoft_dirty(pmd return pmd_set_flags(pmd, _PAGE_SOFT_DIRTY); } +static inline pte_t pte_swp_mksoft_dirty(pte_t pte) +{ + return pte_set_flags(pte, _PAGE_SWP_SOFT_DIRTY); +} + +static inline int pte_swp_soft_dirty(pte_t pte) +{ + return pte_flags(pte) & _PAGE_SWP_SOFT_DIRTY; +} + +static inline pte_t pte_swp_clear_soft_dirty(pte_t pte) +{ + return pte_clear_flags(pte, _PAGE_SWP_SOFT_DIRTY); +} + /* * Mask out unsupported bits in a present pgprot. Non-present pgprots * can use those bits for other purposes, so leave them be. Index: linux-2.6.git/arch/x86/include/asm/pgtable_types.h =================================================================== --- linux-2.6.git.orig/arch/x86/include/asm/pgtable_types.h +++ linux-2.6.git/arch/x86/include/asm/pgtable_types.h @@ -67,6 +67,19 @@ #define _PAGE_SOFT_DIRTY (_AT(pteval_t, 0)) #endif +/* + * Tracking soft dirty bit when a page goes to a swap is tricky. + * We need a bit which can be stored in pte _and_ not conflict + * with swap entry format. On x86 bits 6 and 7 are *not* involved + * into swap entry computation, but bit 6 is used for nonlinear + * file mapping, so we borrow bit 7 for soft dirty tracking. + */ +#ifdef CONFIG_MEM_SOFT_DIRTY +#define _PAGE_SWP_SOFT_DIRTY _PAGE_PSE +#else +#define _PAGE_SWP_SOFT_DIRTY (_AT(pteval_t, 0)) +#endif + #if defined(CONFIG_X86_64) || defined(CONFIG_X86_PAE) #define _PAGE_NX (_AT(pteval_t, 1) << _PAGE_BIT_NX) #else Index: linux-2.6.git/fs/proc/task_mmu.c =================================================================== --- linux-2.6.git.orig/fs/proc/task_mmu.c +++ linux-2.6.git/fs/proc/task_mmu.c @@ -730,8 +730,14 @@ static inline void clear_soft_dirty(stru * of how soft-dirty works. */ pte_t ptent = *pte; - ptent = pte_wrprotect(ptent); - ptent = pte_clear_flags(ptent, _PAGE_SOFT_DIRTY); + + if (pte_present(ptent)) { + ptent = pte_wrprotect(ptent); + ptent = pte_clear_flags(ptent, _PAGE_SOFT_DIRTY); + } else if (is_swap_pte(ptent)) { + ptent = pte_swp_clear_soft_dirty(ptent); + } + set_pte_at(vma->vm_mm, addr, pte, ptent); #endif } @@ -752,14 +758,15 @@ static int clear_refs_pte_range(pmd_t *p pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl); for (; addr != end; pte++, addr += PAGE_SIZE) { ptent = *pte; - if (!pte_present(ptent)) - continue; if (cp->type == CLEAR_REFS_SOFT_DIRTY) { clear_soft_dirty(vma, addr, pte); continue; } + if (!pte_present(ptent)) + continue; + page = vm_normal_page(vma, addr, ptent); if (!page) continue; @@ -930,8 +937,10 @@ static void pte_to_pagemap_entry(pagemap flags = PM_PRESENT; page = vm_normal_page(vma, addr, pte); } else if (is_swap_pte(pte)) { - swp_entry_t entry = pte_to_swp_entry(pte); - + swp_entry_t entry; + if (pte_swp_soft_dirty(pte)) + flags2 |= __PM_SOFT_DIRTY; + entry = pte_to_swp_entry(pte); frame = swp_type(entry) | (swp_offset(entry) << MAX_SWAPFILES_SHIFT); flags = PM_SWAP; Index: linux-2.6.git/include/asm-generic/pgtable.h =================================================================== --- linux-2.6.git.orig/include/asm-generic/pgtable.h +++ linux-2.6.git/include/asm-generic/pgtable.h @@ -417,6 +417,21 @@ static inline pmd_t pmd_mksoft_dirty(pmd { return pmd; } + +static inline pte_t pte_swp_mksoft_dirty(pte_t pte) +{ + return pte; +} + +static inline int pte_swp_soft_dirty(pte_t pte) +{ + return 0; +} + +static inline pte_t pte_swp_clear_soft_dirty(pte_t pte) +{ + return pte; +} #endif #ifndef __HAVE_PFNMAP_TRACKING Index: linux-2.6.git/include/linux/swapops.h =================================================================== --- linux-2.6.git.orig/include/linux/swapops.h +++ linux-2.6.git/include/linux/swapops.h @@ -67,6 +67,8 @@ static inline swp_entry_t pte_to_swp_ent swp_entry_t arch_entry; BUG_ON(pte_file(pte)); + if (pte_swp_soft_dirty(pte)) + pte = pte_swp_clear_soft_dirty(pte); arch_entry = __pte_to_swp_entry(pte); return swp_entry(__swp_type(arch_entry), __swp_offset(arch_entry)); } Index: linux-2.6.git/mm/memory.c =================================================================== --- linux-2.6.git.orig/mm/memory.c +++ linux-2.6.git/mm/memory.c @@ -3115,6 +3115,8 @@ static int do_swap_page(struct mm_struct exclusive = 1; } flush_icache_page(vma, page); + if (pte_swp_soft_dirty(orig_pte)) + pte = pte_mksoft_dirty(pte); set_pte_at(mm, address, page_table, pte); if (page == swapcache) do_page_add_anon_rmap(page, vma, address, exclusive); Index: linux-2.6.git/mm/rmap.c =================================================================== --- linux-2.6.git.orig/mm/rmap.c +++ linux-2.6.git/mm/rmap.c @@ -1236,6 +1236,7 @@ int try_to_unmap_one(struct page *page, swp_entry_to_pte(make_hwpoison_entry(page))); } else if (PageAnon(page)) { swp_entry_t entry = { .val = page_private(page) }; + pte_t swp_pte; if (PageSwapCache(page)) { /* @@ -1264,7 +1265,10 @@ int try_to_unmap_one(struct page *page, BUG_ON(TTU_ACTION(flags) != TTU_MIGRATION); entry = make_migration_entry(page, pte_write(pteval)); } - set_pte_at(mm, address, pte, swp_entry_to_pte(entry)); + swp_pte = swp_entry_to_pte(entry); + if (pte_soft_dirty(pteval)) + swp_pte = pte_swp_mksoft_dirty(swp_pte); + set_pte_at(mm, address, pte, swp_pte); BUG_ON(pte_file(*pte)); } else if (IS_ENABLED(CONFIG_MIGRATION) && (TTU_ACTION(flags) == TTU_MIGRATION)) { Index: linux-2.6.git/mm/swapfile.c =================================================================== --- linux-2.6.git.orig/mm/swapfile.c +++ linux-2.6.git/mm/swapfile.c @@ -866,6 +866,21 @@ unsigned int count_swap_pages(int type, } #endif /* CONFIG_HIBERNATION */ +static inline int maybe_same_pte(pte_t pte, pte_t swp_pte) +{ +#ifdef CONFIG_MEM_SOFT_DIRTY + /* + * When pte keeps soft dirty bit the pte generated + * from swap entry does not has it, still it's same + * pte from logical point of view. + */ + pte_t swp_pte_dirty = pte_swp_mksoft_dirty(swp_pte); + return pte_same(pte, swp_pte) || pte_same(pte, swp_pte_dirty); +#else + return pte_same(pte, swp_pte); +#endif +} + /* * No need to decide whether this PTE shares the swap entry with others, * just let do_wp_page work it out if a write is requested later - to @@ -892,7 +907,7 @@ static int unuse_pte(struct vm_area_stru } pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl); - if (unlikely(!pte_same(*pte, swp_entry_to_pte(entry)))) { + if (unlikely(!maybe_same_pte(*pte, swp_entry_to_pte(entry)))) { mem_cgroup_cancel_charge_swapin(memcg); ret = 0; goto out; @@ -947,7 +962,7 @@ static int unuse_pte_range(struct vm_are * swapoff spends a _lot_ of time in this loop! * Test inline before going to call unuse_pte. */ - if (unlikely(pte_same(*pte, swp_pte))) { + if (unlikely(maybe_same_pte(*pte, swp_pte))) { pte_unmap(pte); ret = unuse_pte(vma, pmd, addr, entry, page); if (ret) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
