From 81d0fa623c5b8dbd5279d9713094b0f9b0a00fb4 Mon Sep 17 00:00:00 2001 From: Peter Feiner Date: Thu, 9 Oct 2014 15:28:32 -0700 Subject: [PATCH] mm: softdirty: unmapped addresses between VMAs are clean If a /proc/pid/pagemap read spans a [VMA, an unmapped region, then a VM_SOFTDIRTY VMA], the virtual pages in the unmapped region are reported as softdirty. Here's a program to demonstrate the bug: int main() { const uint64_t PAGEMAP_SOFTDIRTY = 1ul << 55; uint64_t pme[3]; int fd = open("/proc/self/pagemap", O_RDONLY);; char *m = mmap(NULL, 3 * getpagesize(), PROT_READ, MAP_ANONYMOUS | MAP_SHARED, -1, 0); munmap(m + getpagesize(), getpagesize()); pread(fd, pme, 24, (unsigned long) m / getpagesize() * 8); assert(pme[0] & PAGEMAP_SOFTDIRTY); /* passes */ assert(!(pme[1] & PAGEMAP_SOFTDIRTY)); /* fails */ assert(pme[2] & PAGEMAP_SOFTDIRTY); /* passes */ return 0; } (Note that all pages in new VMAs are softdirty until cleared). Tested: Used the program given above. I'm going to include this code in a selftest in the future. [n-horiguchi@ah.jp.nec.com: prevent pagemap_pte_range() from overrunning] Signed-off-by: Peter Feiner Cc: "Kirill A. Shutemov" Cc: Cyrill Gorcunov Cc: Pavel Emelyanov Cc: Jamie Liu Cc: Hugh Dickins Cc: Naoya Horiguchi Signed-off-by: Naoya Horiguchi Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/proc/task_mmu.c | 61 ++++++++++++++++++++++++++++++---------------- 1 file changed, 40 insertions(+), 21 deletions(-) diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index 1acec26a3758..b7a7dc963a35 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -1027,7 +1027,6 @@ static int pagemap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end, spinlock_t *ptl; pte_t *pte; int err = 0; - pagemap_entry_t pme = make_pme(PM_NOT_PRESENT(pm->v2)); /* find the first VMA at or above 'addr' */ vma = find_vma(walk->mm, addr); @@ -1041,6 +1040,7 @@ static int pagemap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end, for (; addr != end; addr += PAGE_SIZE) { unsigned long offset; + pagemap_entry_t pme; offset = (addr & ~PAGEMAP_WALK_MASK) >> PAGE_SHIFT; @@ -1055,32 +1055,51 @@ static int pagemap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end, if (pmd_trans_unstable(pmd)) return 0; - for (; addr != end; addr += PAGE_SIZE) { - int flags2; - - /* check to see if we've left 'vma' behind - * and need a new, higher one */ - if (vma && (addr >= vma->vm_end)) { - vma = find_vma(walk->mm, addr); - if (vma && (vma->vm_flags & VM_SOFTDIRTY)) - flags2 = __PM_SOFT_DIRTY; - else - flags2 = 0; - pme = make_pme(PM_NOT_PRESENT(pm->v2) | PM_STATUS2(pm->v2, flags2)); + + while (1) { + /* End of address space hole, which we mark as non-present. */ + unsigned long hole_end; + + if (vma) + hole_end = min(end, vma->vm_start); + else + hole_end = end; + + for (; addr < hole_end; addr += PAGE_SIZE) { + pagemap_entry_t pme = make_pme(PM_NOT_PRESENT(pm->v2)); + + err = add_to_pagemap(addr, &pme, pm); + if (err) + return err; } - /* check that 'vma' actually covers this address, - * and that it isn't a huge page vma */ - if (vma && (vma->vm_start <= addr) && - !is_vm_hugetlb_page(vma)) { + if (!vma || vma->vm_start >= end) + break; + /* + * We can't possibly be in a hugetlb VMA. In general, + * for a mm_walk with a pmd_entry and a hugetlb_entry, + * the pmd_entry can only be called on addresses in a + * hugetlb if the walk starts in a non-hugetlb VMA and + * spans a hugepage VMA. Since pagemap_read walks are + * PMD-sized and PMD-aligned, this will never be true. + */ + BUG_ON(is_vm_hugetlb_page(vma)); + + /* Addresses in the VMA. */ + for (; addr < min(end, vma->vm_end); addr += PAGE_SIZE) { + pagemap_entry_t pme; pte = pte_offset_map(pmd, addr); pte_to_pagemap_entry(&pme, pm, vma, addr, *pte); - /* unmap before userspace copy */ pte_unmap(pte); + err = add_to_pagemap(addr, &pme, pm); + if (err) + return err; } - err = add_to_pagemap(addr, &pme, pm); - if (err) - return err; + + if (addr == end) + break; + + vma = find_vma(walk->mm, addr); } cond_resched(); -- 2.30.2