5 files changed, 61 insertions, 12 deletions

diff --git a/Documentation/vm/soft-dirty.txt b/Documentation/vm/soft-dirty.txt
index 9a12a5956bc0..55684d11a1e8 100644
--- a/Documentation/vm/soft-dirty.txt
+++ b/Documentation/vm/soft-dirty.txt
@@ -28,6 +28,13 @@ This is so, since the pages are still mapped to physical memory, and thus all
 the kernel does is finds this fact out and puts both writable and soft-dirty
 bits on the PTE.
 
+  While in most cases tracking memory changes by #PF-s is more than enough
+there is still a scenario when we can lose soft dirty bits -- a task
+unmaps a previously mapped memory region and then maps a new one at exactly
+the same place. When unmap is called, the kernel internally clears PTE values
+including soft dirty bits. To notify user space application about such
+memory region renewal the kernel always marks new memory regions (and
+expanded regions) as soft dirty.
 
   This feature is actively used by the checkpoint-restore project. You
 can find more details about it on http://criu.org
diff --git a/fs/exec.c b/fs/exec.c
index fd774c7cb483..2d1e52a58fe9 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -266,7 +266,7 @@ static int __bprm_mm_init(struct linux_binprm *bprm)
         BUILD_BUG_ON(VM_STACK_FLAGS & VM_STACK_INCOMPLETE_SETUP);
         vma->vm_end = STACK_TOP_MAX;
         vma->vm_start = vma->vm_end - PAGE_SIZE;
-        vma->vm_flags = VM_STACK_FLAGS | VM_STACK_INCOMPLETE_SETUP;
+        vma->vm_flags = VM_SOFTDIRTY | VM_STACK_FLAGS | VM_STACK_INCOMPLETE_SETUP;
         vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
         INIT_LIST_HEAD(&vma->anon_vma_chain);
 
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 107d026f5d6e..09228639b83d 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -740,6 +740,9 @@ static inline void clear_soft_dirty(struct vm_area_struct *vma,
                 ptent = pte_file_clear_soft_dirty(ptent);
         }
 
+        if (vma->vm_flags & VM_SOFTDIRTY)
+                vma->vm_flags &= ~VM_SOFTDIRTY;
+
         set_pte_at(vma->vm_mm, addr, pte, ptent);
 #endif
 }
@@ -949,13 +952,15 @@ static void pte_to_pagemap_entry(pagemap_entry_t *pme, struct pagemapread *pm,
                 if (is_migration_entry(entry))
                         page = migration_entry_to_page(entry);
         } else {
-                *pme = make_pme(PM_NOT_PRESENT(pm->v2));
+                if (vma->vm_flags & VM_SOFTDIRTY)
+                        flags2 |= __PM_SOFT_DIRTY;
+                *pme = make_pme(PM_NOT_PRESENT(pm->v2) | PM_STATUS2(pm->v2, flags2));
                 return;
         }
 
         if (page && !PageAnon(page))
                 flags |= PM_FILE;
-        if (pte_soft_dirty(pte))
+        if ((vma->vm_flags & VM_SOFTDIRTY) || pte_soft_dirty(pte))
                 flags2 |= __PM_SOFT_DIRTY;
 
         *pme = make_pme(PM_PFRAME(frame) | PM_STATUS2(pm->v2, flags2) | flags);
@@ -974,7 +979,7 @@ static void thp_pmd_to_pagemap_entry(pagemap_entry_t *pme, struct pagemapread *p
                 *pme = make_pme(PM_PFRAME(pmd_pfn(pmd) + offset)
                                 | PM_STATUS2(pm->v2, pmd_flags2) | PM_PRESENT);
         else
-                *pme = make_pme(PM_NOT_PRESENT(pm->v2));
+                *pme = make_pme(PM_NOT_PRESENT(pm->v2) | PM_STATUS2(pm->v2, pmd_flags2));
 }
 #else
 static inline void thp_pmd_to_pagemap_entry(pagemap_entry_t *pme, struct pagemapread *pm,
@@ -997,7 +1002,11 @@ static int pagemap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
         if (vma && pmd_trans_huge_lock(pmd, vma) == 1) {
                 int pmd_flags2;
 
-                pmd_flags2 = (pmd_soft_dirty(*pmd) ? __PM_SOFT_DIRTY : 0);
+                if ((vma->vm_flags & VM_SOFTDIRTY) || pmd_soft_dirty(*pmd))
+                        pmd_flags2 = __PM_SOFT_DIRTY;
+                else
+                        pmd_flags2 = 0;
+
                 for (; addr != end; addr += PAGE_SIZE) {
                         unsigned long offset;
 
@@ -1015,12 +1024,17 @@ 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);
-                        pme = make_pme(PM_NOT_PRESENT(pm->v2));
+                        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));
                 }
 
                 /* check that 'vma' actually covers this address,
@@ -1044,13 +1058,15 @@ static int pagemap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
 
 #ifdef CONFIG_HUGETLB_PAGE
 static void huge_pte_to_pagemap_entry(pagemap_entry_t *pme, struct pagemapread *pm,
-                                        pte_t pte, int offset)
+                                        pte_t pte, int offset, int flags2)
 {
         if (pte_present(pte))
-                *pme = make_pme(PM_PFRAME(pte_pfn(pte) + offset)
-                                | PM_STATUS2(pm->v2, 0) | PM_PRESENT);
+                *pme = make_pme(PM_PFRAME(pte_pfn(pte) + offset)        |
+                                PM_STATUS2(pm->v2, flags2)              |
+                                PM_PRESENT);
         else
-                *pme = make_pme(PM_NOT_PRESENT(pm->v2));
+                *pme = make_pme(PM_NOT_PRESENT(pm->v2)                  |
+                                PM_STATUS2(pm->v2, flags2));
 }
 
 /* This function walks within one hugetlb entry in the single call */
@@ -1059,12 +1075,22 @@ static int pagemap_hugetlb_range(pte_t *pte, unsigned long hmask,
                                  struct mm_walk *walk)
 {
         struct pagemapread *pm = walk->private;
+        struct vm_area_struct *vma;
         int err = 0;
+        int flags2;
         pagemap_entry_t pme;
 
+        vma = find_vma(walk->mm, addr);
+        WARN_ON_ONCE(!vma);
+
+        if (vma && (vma->vm_flags & VM_SOFTDIRTY))
+                flags2 = __PM_SOFT_DIRTY;
+        else
+                flags2 = 0;
+
         for (; addr != end; addr += PAGE_SIZE) {
                 int offset = (addr & ~hmask) >> PAGE_SHIFT;
-                huge_pte_to_pagemap_entry(&pme, pm, *pte, offset);
+                huge_pte_to_pagemap_entry(&pme, pm, *pte, offset, flags2);
                 err = add_to_pagemap(addr, &pme, pm);
                 if (err)
                         return err;
diff --git a/include/linux/mm.h b/include/linux/mm.h
index d2d59b4149d0..dce24569f8fc 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -115,6 +115,12 @@ extern unsigned int kobjsize(const void *objp);
 #define VM_ARCH_1       0x01000000      /* Architecture-specific flag */
 #define VM_DONTDUMP     0x04000000      /* Do not include in the core dump */
 
+#ifdef CONFIG_MEM_SOFT_DIRTY
+# define VM_SOFTDIRTY   0x08000000      /* Not soft dirty clean area */
+#else
+# define VM_SOFTDIRTY   0
+#endif
+
 #define VM_MIXEDMAP     0x10000000      /* Can contain "struct page" and pure PFN pages */
 #define VM_HUGEPAGE     0x20000000      /* MADV_HUGEPAGE marked this vma */
 #define VM_NOHUGEPAGE   0x40000000      /* MADV_NOHUGEPAGE marked this vma */
diff --git a/mm/mmap.c b/mm/mmap.c
index 13926a5a6901..51958d192a48 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1609,6 +1609,15 @@ out:
         if (file)
                 uprobe_mmap(vma);
 
+        /*
+         * New (or expanded) vma always get soft dirty status.
+         * Otherwise user-space soft-dirty page tracker won't
+         * be able to distinguish situation when vma area unmapped,
+         * then new mapped in-place (which must be aimed as
+         * a completely new data area).
+         */
+        vma->vm_flags |= VM_SOFTDIRTY;
+
         return addr;
 
 unmap_and_free_vma:
@@ -2652,6 +2661,7 @@ out:
         mm->total_vm += len >> PAGE_SHIFT;
         if (flags & VM_LOCKED)
                 mm->locked_vm += (len >> PAGE_SHIFT);
+        vma->vm_flags |= VM_SOFTDIRTY;
         return addr;
 }
 
@@ -2916,7 +2926,7 @@ int install_special_mapping(struct mm_struct *mm,
         vma->vm_start = addr;
         vma->vm_end = addr + len;
 
-        vma->vm_flags = vm_flags | mm->def_flags | VM_DONTEXPAND;
+        vma->vm_flags = vm_flags | mm->def_flags | VM_DONTEXPAND | VM_SOFTDIRTY;
         vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
 
         vma->vm_ops = &special_mapping_vmops;