mm/thp: fix vma_address() if virtual address below file offset

Running certain tests with a DEBUG_VM kernel would crash within hours,
on the total_mapcount BUG() in split_huge_page_to_list(), while trying
to free up some memory by punching a hole in a shmem huge page: split's
try_to_unmap() was unable to find all the mappings of the page (which,
on a !DEBUG_VM kernel, would then keep the huge page pinned in memory).

When that BUG() was changed to a WARN(), it would later crash on the
VM_BUG_ON_VMA(end < vma->vm_start || start >= vma->vm_end, vma) in
mm/internal.h:vma_address(), used by rmap_walk_file() for
try_to_unmap().

vma_address() is usually correct, but there's a wraparound case when the
vm_start address is unusually low, but vm_pgoff not so low:
vma_address() chooses max(start, vma->vm_start), but that decides on the
wrong address, because start has become almost ULONG_MAX.

Rewrite vma_address() to be more careful about vm_pgoff; move the
VM_BUG_ON_VMA() out of it, returning -EFAULT for errors, so that it can
be safely used from page_mapped_in_vma() and page_address_in_vma() too.

Add vma_address_end() to apply similar care to end address calculation,
in page_vma_mapped_walk() and page_mkclean_one() and try_to_unmap_one();
though it raises a question of whether callers would do better to supply
pvmw->end to page_vma_mapped_walk() - I chose not, for a smaller patch.

An irritation is that their apparent generality breaks down on KSM
pages, which cannot be located by the page->index that page_to_pgoff()
uses: as commit 4b0ece6fa016 ("mm: migrate: fix remove_migration_pte()
for ksm pages") once discovered.  I dithered over the best thing to do
about that, and have ended up with a VM_BUG_ON_PAGE(PageKsm) in both
vma_address() and vma_address_end(); though the only place in danger of
using it on them was try_to_unmap_one().

Sidenote: vma_address() and vma_address_end() now use compound_nr() on a
head page, instead of thp_size(): to make the right calculation on a
hugetlbfs page, whether or not THPs are configured.  try_to_unmap() is
used on hugetlbfs pages, but perhaps the wrong calculation never
mattered.

Link: https://lkml.kernel.org/r/caf1c1a3-7cfb-7f8f-1beb-ba816e932825@google.com
Fixes: a8fa41ad2f6f ("mm, rmap: check all VMAs that PTE-mapped THP can be part of")
Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jue Wang <juew@google.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Wang Yugui <wangyugui@e16-tech.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/internal.h b/mm/internal.h
index 2f11829..e8fdb53 100644 (file)
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -384,27 +384,52 @@ static inline void mlock_migrate_page(struct page *newpage, struct page *page)
 extern pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma);
 
 /*
- * At what user virtual address is page expected in @vma?
+ * At what user virtual address is page expected in vma?
+ * Returns -EFAULT if all of the page is outside the range of vma.
+ * If page is a compound head, the entire compound page is considered.
  */
 static inline unsigned long
-__vma_address(struct page *page, struct vm_area_struct *vma)
+vma_address(struct page *page, struct vm_area_struct *vma)
 {
-       pgoff_t pgoff = page_to_pgoff(page);
-       return vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
+       pgoff_t pgoff;
+       unsigned long address;
+
+       VM_BUG_ON_PAGE(PageKsm(page), page);    /* KSM page->index unusable */
+       pgoff = page_to_pgoff(page);
+       if (pgoff >= vma->vm_pgoff) {
+               address = vma->vm_start +
+                       ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
+               /* Check for address beyond vma (or wrapped through 0?) */
+               if (address < vma->vm_start || address >= vma->vm_end)
+                       address = -EFAULT;
+       } else if (PageHead(page) &&
+                  pgoff + compound_nr(page) - 1 >= vma->vm_pgoff) {
+               /* Test above avoids possibility of wrap to 0 on 32-bit */
+               address = vma->vm_start;
+       } else {
+               address = -EFAULT;
+       }
+       return address;
 }
 
+/*
+ * Then at what user virtual address will none of the page be found in vma?
+ * Assumes that vma_address() already returned a good starting address.
+ * If page is a compound head, the entire compound page is considered.
+ */
 static inline unsigned long
-vma_address(struct page *page, struct vm_area_struct *vma)
+vma_address_end(struct page *page, struct vm_area_struct *vma)
 {
-       unsigned long start, end;
-
-       start = __vma_address(page, vma);
-       end = start + thp_size(page) - PAGE_SIZE;
-
-       /* page should be within @vma mapping range */
-       VM_BUG_ON_VMA(end < vma->vm_start || start >= vma->vm_end, vma);
-
-       return max(start, vma->vm_start);
+       pgoff_t pgoff;
+       unsigned long address;
+
+       VM_BUG_ON_PAGE(PageKsm(page), page);    /* KSM page->index unusable */
+       pgoff = page_to_pgoff(page) + compound_nr(page);
+       address = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
+       /* Check for address beyond vma (or wrapped through 0?) */
+       if (address < vma->vm_start || address > vma->vm_end)
+               address = vma->vm_end;
+       return address;
 }
 
 static inline struct file *maybe_unlock_mmap_for_io(struct vm_fault *vmf,

diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
index 5b55996..e37bd43 100644 (file)
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c
@@ -228,18 +228,18 @@ restart:
        if (!map_pte(pvmw))
                goto next_pte;
        while (1) {
+               unsigned long end;
+
                if (check_pte(pvmw))
                        return true;
 next_pte:
                /* Seek to next pte only makes sense for THP */
                if (!PageTransHuge(pvmw->page) || PageHuge(pvmw->page))
                        return not_found(pvmw);
+               end = vma_address_end(pvmw->page, pvmw->vma);
                do {
                        pvmw->address += PAGE_SIZE;
-                       if (pvmw->address >= pvmw->vma->vm_end ||
-                           pvmw->address >=
-                                       __vma_address(pvmw->page, pvmw->vma) +
-                                       thp_size(pvmw->page))
+                       if (pvmw->address >= end)
                                return not_found(pvmw);
                        /* Did we cross page table boundary? */
                        if (pvmw->address % PMD_SIZE == 0) {
@@ -277,14 +277,10 @@ int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma)
                .vma = vma,
                .flags = PVMW_SYNC,
        };
-       unsigned long start, end;
-
-       start = __vma_address(page, vma);
-       end = start + thp_size(page) - PAGE_SIZE;
 
-       if (unlikely(end < vma->vm_start || start >= vma->vm_end))
+       pvmw.address = vma_address(page, vma);
+       if (pvmw.address == -EFAULT)
                return 0;
-       pvmw.address = max(start, vma->vm_start);
        if (!page_vma_mapped_walk(&pvmw))
                return 0;
        page_vma_mapped_walk_done(&pvmw);

diff --git a/mm/rmap.c b/mm/rmap.c
index 07811b4..144de54 100644 (file)
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -707,7 +707,6 @@ static bool should_defer_flush(struct mm_struct *mm, enum ttu_flags flags)
  */
 unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma)
 {
-       unsigned long address;
        if (PageAnon(page)) {
                struct anon_vma *page__anon_vma = page_anon_vma(page);
                /*
@@ -722,10 +721,8 @@ unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma)
                        return -EFAULT;
        } else
                return -EFAULT;
-       address = __vma_address(page, vma);
-       if (unlikely(address < vma->vm_start || address >= vma->vm_end))
-               return -EFAULT;
-       return address;
+
+       return vma_address(page, vma);
 }
 
 pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address)
@@ -919,7 +916,7 @@ static bool page_mkclean_one(struct page *page, struct vm_area_struct *vma,
         */
        mmu_notifier_range_init(&range, MMU_NOTIFY_PROTECTION_PAGE,
                                0, vma, vma->vm_mm, address,
-                               min(vma->vm_end, address + page_size(page)));
+                               vma_address_end(page, vma));
        mmu_notifier_invalidate_range_start(&range);
 
        while (page_vma_mapped_walk(&pvmw)) {
@@ -1435,9 +1432,10 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
         * Note that the page can not be free in this function as call of
         * try_to_unmap() must hold a reference on the page.
         */
+       range.end = PageKsm(page) ?
+                       address + PAGE_SIZE : vma_address_end(page, vma);
        mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, vma->vm_mm,
-                               address,
-                               min(vma->vm_end, address + page_size(page)));
+                               address, range.end);
        if (PageHuge(page)) {
                /*
                 * If sharing is possible, start and end will be adjusted
@@ -1889,6 +1887,7 @@ static void rmap_walk_anon(struct page *page, struct rmap_walk_control *rwc,
                struct vm_area_struct *vma = avc->vma;
                unsigned long address = vma_address(page, vma);
 
+               VM_BUG_ON_VMA(address == -EFAULT, vma);
                cond_resched();
 
                if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg))
@@ -1943,6 +1942,7 @@ static void rmap_walk_file(struct page *page, struct rmap_walk_control *rwc,
                        pgoff_start, pgoff_end) {
                unsigned long address = vma_address(page, vma);
 
+               VM_BUG_ON_VMA(address == -EFAULT, vma);
                cond_resched();
 
                if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg))