From 68b5a652485682f67eacdee3deae640fb7845b63 Mon Sep 17 00:00:00 2001 From: Peter Feiner Date: Wed, 6 Aug 2014 16:08:09 -0700 Subject: [PATCH] mm: softdirty: respect VM_SOFTDIRTY in PTE holes After a VMA is created with the VM_SOFTDIRTY flag set, /proc/pid/pagemap should report that the VMA's virtual pages are soft-dirty until VM_SOFTDIRTY is cleared (i.e., by the next write of "4" to /proc/pid/clear_refs). However, pagemap ignores the VM_SOFTDIRTY flag for virtual addresses that fall in PTE holes (i.e., virtual addresses that don't have a PMD, PUD, or PGD allocated yet). To observe this bug, use mmap to create a VMA large enough such that there's a good chance that the VMA will occupy an unused PMD, then test the soft-dirty bit on its pages. In practice, I found that a VMA that covered a PMD's worth of address space was big enough. This patch adds the necessary VMA lookup to the PTE hole callback in /proc/pid/pagemap's page walk and sets soft-dirty according to the VMAs' VM_SOFTDIRTY flag. Signed-off-by: Peter Feiner Acked-by: Cyrill Gorcunov Cc: Pavel Emelyanov Cc: Hugh Dickins Acked-by: Naoya Horiguchi Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/proc/task_mmu.c | 27 +++++++++++++++++++++------ 1 file changed, 21 insertions(+), 6 deletions(-) diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index cfa63ee92c96..dfc791c42d64 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -925,15 +925,30 @@ static int pagemap_pte_hole(unsigned long start, unsigned long end, struct mm_walk *walk) { struct pagemapread *pm = walk->private; - unsigned long addr; + unsigned long addr = start; int err = 0; - pagemap_entry_t pme = make_pme(PM_NOT_PRESENT(pm->v2)); - for (addr = start; addr < end; addr += PAGE_SIZE) { - err = add_to_pagemap(addr, &pme, pm); - if (err) - break; + while (addr < end) { + struct vm_area_struct *vma = find_vma(walk->mm, addr); + pagemap_entry_t pme = make_pme(PM_NOT_PRESENT(pm->v2)); + unsigned long vm_end; + + if (!vma) { + vm_end = end; + } else { + vm_end = min(end, vma->vm_end); + if (vma->vm_flags & VM_SOFTDIRTY) + pme.pme |= PM_STATUS2(pm->v2, __PM_SOFT_DIRTY); + } + + for (; addr < vm_end; addr += PAGE_SIZE) { + err = add_to_pagemap(addr, &pme, pm); + if (err) + goto out; + } } + +out: return err; } -- 2.20.1