summaryrefslogtreecommitdiff
path: root/mm
diff options
context:
space:
mode:
authorPeter Feiner <pfeiner@google.com>2014-10-13 15:55:46 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-10-14 02:18:28 +0200
commit64e455079e1bd7787cc47be30b7f601ce682a5f6 (patch)
tree05193bd91be3ffc0d33ddd3ffb654ef4c23778f9 /mm
parent63a12d9d01831208a47f5c0fbbf93f503d1fb162 (diff)
downloadlinux-sh-64e455079e1bd7787cc47be30b7f601ce682a5f6.tar.gz
mm: softdirty: enable write notifications on VMAs after VM_SOFTDIRTY cleared
For VMAs that don't want write notifications, PTEs created for read faults have their write bit set. If the read fault happens after VM_SOFTDIRTY is cleared, then the PTE's softdirty bit will remain clear after subsequent writes. Here's a simple code snippet to demonstrate the bug: char* m = mmap(NULL, getpagesize(), PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_SHARED, -1, 0); system("echo 4 > /proc/$PPID/clear_refs"); /* clear VM_SOFTDIRTY */ assert(*m == '\0'); /* new PTE allows write access */ assert(!soft_dirty(x)); *m = 'x'; /* should dirty the page */ assert(soft_dirty(x)); /* fails */ With this patch, write notifications are enabled when VM_SOFTDIRTY is cleared. Furthermore, to avoid unnecessary faults, write notifications are disabled when VM_SOFTDIRTY is set. As a side effect of enabling and disabling write notifications with care, this patch fixes a bug in mprotect where vm_page_prot bits set by drivers were zapped on mprotect. An analogous bug was fixed in mmap by commit c9d0bf241451 ("mm: uncached vma support with writenotify"). Signed-off-by: Peter Feiner <pfeiner@google.com> Reported-by: Peter Feiner <pfeiner@google.com> Suggested-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Cyrill Gorcunov <gorcunov@openvz.org> Cc: Pavel Emelyanov <xemul@parallels.com> Cc: Jamie Liu <jamieliu@google.com> Cc: Hugh Dickins <hughd@google.com> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Cc: Bjorn Helgaas <bhelgaas@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/memory.c3
-rw-r--r--mm/mmap.c45
-rw-r--r--mm/mprotect.c20
3 files changed, 35 insertions, 33 deletions
diff --git a/mm/memory.c b/mm/memory.c
index e229970e4223..1cc6bfbd872e 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2053,7 +2053,8 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
old_page = vm_normal_page(vma, address, orig_pte);
if (!old_page) {
/*
- * VM_MIXEDMAP !pfn_valid() case
+ * VM_MIXEDMAP !pfn_valid() case, or VM_SOFTDIRTY clear on a
+ * VM_PFNMAP VMA.
*
* We should not cow pages in a shared writeable mapping.
* Just mark the pages writable as we can't do any dirty
diff --git a/mm/mmap.c b/mm/mmap.c
index 93d28c7e5420..7f855206e7fb 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -89,6 +89,25 @@ pgprot_t vm_get_page_prot(unsigned long vm_flags)
}
EXPORT_SYMBOL(vm_get_page_prot);
+static pgprot_t vm_pgprot_modify(pgprot_t oldprot, unsigned long vm_flags)
+{
+ return pgprot_modify(oldprot, vm_get_page_prot(vm_flags));
+}
+
+/* Update vma->vm_page_prot to reflect vma->vm_flags. */
+void vma_set_page_prot(struct vm_area_struct *vma)
+{
+ unsigned long vm_flags = vma->vm_flags;
+
+ vma->vm_page_prot = vm_pgprot_modify(vma->vm_page_prot, vm_flags);
+ if (vma_wants_writenotify(vma)) {
+ vm_flags &= ~VM_SHARED;
+ vma->vm_page_prot = vm_pgprot_modify(vma->vm_page_prot,
+ vm_flags);
+ }
+}
+
+
int sysctl_overcommit_memory __read_mostly = OVERCOMMIT_GUESS; /* heuristic overcommit */
int sysctl_overcommit_ratio __read_mostly = 50; /* default is 50% */
unsigned long sysctl_overcommit_kbytes __read_mostly;
@@ -1475,11 +1494,16 @@ int vma_wants_writenotify(struct vm_area_struct *vma)
if (vma->vm_ops && vma->vm_ops->page_mkwrite)
return 1;
- /* The open routine did something to the protections already? */
+ /* The open routine did something to the protections that pgprot_modify
+ * won't preserve? */
if (pgprot_val(vma->vm_page_prot) !=
- pgprot_val(vm_get_page_prot(vm_flags)))
+ pgprot_val(vm_pgprot_modify(vma->vm_page_prot, vm_flags)))
return 0;
+ /* Do we need to track softdirty? */
+ if (IS_ENABLED(CONFIG_MEM_SOFT_DIRTY) && !(vm_flags & VM_SOFTDIRTY))
+ return 1;
+
/* Specialty mapping? */
if (vm_flags & VM_PFNMAP)
return 0;
@@ -1615,21 +1639,6 @@ munmap_back:
goto free_vma;
}
- if (vma_wants_writenotify(vma)) {
- pgprot_t pprot = vma->vm_page_prot;
-
- /* Can vma->vm_page_prot have changed??
- *
- * Answer: Yes, drivers may have changed it in their
- * f_op->mmap method.
- *
- * Ensures that vmas marked as uncached stay that way.
- */
- vma->vm_page_prot = vm_get_page_prot(vm_flags & ~VM_SHARED);
- if (pgprot_val(pprot) == pgprot_val(pgprot_noncached(pprot)))
- vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
- }
-
vma_link(mm, vma, prev, rb_link, rb_parent);
/* Once vma denies write, undo our temporary denial count */
if (file) {
@@ -1663,6 +1672,8 @@ out:
*/
vma->vm_flags |= VM_SOFTDIRTY;
+ vma_set_page_prot(vma);
+
return addr;
unmap_and_free_vma:
diff --git a/mm/mprotect.c b/mm/mprotect.c
index c43d557941f8..ace93454ce8e 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -29,13 +29,6 @@
#include <asm/cacheflush.h>
#include <asm/tlbflush.h>
-#ifndef pgprot_modify
-static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
-{
- return newprot;
-}
-#endif
-
/*
* For a prot_numa update we only hold mmap_sem for read so there is a
* potential race with faulting where a pmd was temporarily none. This
@@ -93,7 +86,9 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
* Avoid taking write faults for pages we
* know to be dirty.
*/
- if (dirty_accountable && pte_dirty(ptent))
+ if (dirty_accountable && pte_dirty(ptent) &&
+ (pte_soft_dirty(ptent) ||
+ !(vma->vm_flags & VM_SOFTDIRTY)))
ptent = pte_mkwrite(ptent);
ptep_modify_prot_commit(mm, addr, pte, ptent);
updated = true;
@@ -320,13 +315,8 @@ success:
* held in write mode.
*/
vma->vm_flags = newflags;
- vma->vm_page_prot = pgprot_modify(vma->vm_page_prot,
- vm_get_page_prot(newflags));
-
- if (vma_wants_writenotify(vma)) {
- vma->vm_page_prot = vm_get_page_prot(newflags & ~VM_SHARED);
- dirty_accountable = 1;
- }
+ dirty_accountable = vma_wants_writenotify(vma);
+ vma_set_page_prot(vma);
change_protection(vma, start, end, vma->vm_page_prot,
dirty_accountable, 0);