numa: fix /proc/<pid>/numa_maps for THP

In gather_pte_stats() a THP pmd is cast into a pte, which is wrong
because the layouts may differ depending on the architecture.  On s390
this will lead to inaccurate numa_maps accounting in /proc because of
misguided pte_present() and pte_dirty() checks on the fake pte.

On other architectures pte_present() and pte_dirty() may work by chance,
but there may be an issue with direct-access (dax) mappings w/o
underlying struct pages when HAVE_PTE_SPECIAL is set and THP is
available.  In vm_normal_page() the fake pte will be checked with
pte_special() and because there is no "special" bit in a pmd, this will
always return false and the VM_PFNMAP | VM_MIXEDMAP checking will be
skipped.  On dax mappings w/o struct pages, an invalid struct page
pointer would then be returned that can crash the kernel.

This patch fixes the numa_maps THP handling by introducing new "_pmd"
variants of the can_gather_numa_stats() and vm_normal_page() functions.

Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Cc: <stable@vger.kernel.org>	[4.3+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 72 insertions, 3 deletions

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 229cb546bee0..541583510cfb 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1518,6 +1518,32 @@ static struct page *can_gather_numa_stats(pte_t pte, struct vm_area_struct *vma,
         return page;
 }
 
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+static struct page *can_gather_numa_stats_pmd(pmd_t pmd,
+                                              struct vm_area_struct *vma,
+                                              unsigned long addr)
+{
+        struct page *page;
+        int nid;
+
+        if (!pmd_present(pmd))
+                return NULL;
+
+        page = vm_normal_page_pmd(vma, addr, pmd);
+        if (!page)
+                return NULL;
+
+        if (PageReserved(page))
+                return NULL;
+
+        nid = page_to_nid(page);
+        if (!node_isset(nid, node_states[N_MEMORY]))
+                return NULL;
+
+        return page;
+}
+#endif
+
 static int gather_pte_stats(pmd_t *pmd, unsigned long addr,
                 unsigned long end, struct mm_walk *walk)
 {
@@ -1527,14 +1553,14 @@ static int gather_pte_stats(pmd_t *pmd, unsigned long addr,
         pte_t *orig_pte;
         pte_t *pte;
 
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
         ptl = pmd_trans_huge_lock(pmd, vma);
         if (ptl) {
-                pte_t huge_pte = *(pte_t *)pmd;
                 struct page *page;
 
-                page = can_gather_numa_stats(huge_pte, vma, addr);
+                page = can_gather_numa_stats_pmd(*pmd, vma, addr);
                 if (page)
-                        gather_stats(page, md, pte_dirty(huge_pte),
+                        gather_stats(page, md, pmd_dirty(*pmd),
                                      HPAGE_PMD_SIZE/PAGE_SIZE);
                 spin_unlock(ptl);
                 return 0;
@@ -1542,6 +1568,7 @@ static int gather_pte_stats(pmd_t *pmd, unsigned long addr,
 
         if (pmd_trans_unstable(pmd))
                 return 0;
+#endif
         orig_pte = pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
         do {
                 struct page *page = can_gather_numa_stats(*pte, vma, addr);
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 79b6c18d0a38..864d7221de84 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1140,6 +1140,8 @@ struct zap_details {
 
 struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
                 pte_t pte);
+struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr,
+                                pmd_t pmd);
 
 int zap_vma_ptes(struct vm_area_struct *vma, unsigned long address,
                 unsigned long size);
diff --git a/mm/memory.c b/mm/memory.c
index 93897f23cc11..305537fc8640 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -789,6 +789,46 @@ out:
         return pfn_to_page(pfn);
 }
 
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr,
+                                pmd_t pmd)
+{
+        unsigned long pfn = pmd_pfn(pmd);
+
+        /*
+         * There is no pmd_special() but there may be special pmds, e.g.
+         * in a direct-access (dax) mapping, so let's just replicate the
+         * !HAVE_PTE_SPECIAL case from vm_normal_page() here.
+         */
+        if (unlikely(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP))) {
+                if (vma->vm_flags & VM_MIXEDMAP) {
+                        if (!pfn_valid(pfn))
+                                return NULL;
+                        goto out;
+                } else {
+                        unsigned long off;
+                        off = (addr - vma->vm_start) >> PAGE_SHIFT;
+                        if (pfn == vma->vm_pgoff + off)
+                                return NULL;
+                        if (!is_cow_mapping(vma->vm_flags))
+                                return NULL;
+                }
+        }
+
+        if (is_zero_pfn(pfn))
+                return NULL;
+        if (unlikely(pfn > highest_memmap_pfn))
+                return NULL;
+
+        /*
+         * NOTE! We still have PageReserved() pages in the page tables.
+         * eg. VDSO mappings can cause them to exist.
+         */
+out:
+        return pfn_to_page(pfn);
+}
+#endif
+
 /*
  * copy one vm_area from one task to the other. Assumes the page tables
  * already present in the new task to be cleared in the whole range