mm: introduce page_vma_mapped_walk()

Introduce a new interface to check if a page is mapped into a vma.  It
aims to address shortcomings of page_check_address{,_transhuge}.

Existing interface is not able to handle PTE-mapped THPs: it only finds
the first PTE.  The rest lefted unnoticed.

page_vma_mapped_walk() iterates over all possible mapping of the page in
the vma.

Link: http://lkml.kernel.org/r/20170129173858.45174-3-kirill.shutemov@linux.intel.com
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 15321fb1df6b5a70263fef971654ec709b1731ba..b76343610653fee971e1ee897fddc9e7bf9e8990 100644 (file)
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -9,6 +9,7 @@
 #include <linux/mm.h>
 #include <linux/rwsem.h>
 #include <linux/memcontrol.h>
+#include <linux/highmem.h>
 
 /*
  * The anon_vma heads a list of private "related" vmas, to scan if
@@ -232,6 +233,31 @@ static inline bool page_check_address_transhuge(struct page *page,
 }
 #endif
 
+/* Avoid racy checks */
+#define PVMW_SYNC              (1 << 0)
+/* Look for migarion entries rather than present PTEs */
+#define PVMW_MIGRATION         (1 << 1)
+
+struct page_vma_mapped_walk {
+       struct page *page;
+       struct vm_area_struct *vma;
+       unsigned long address;
+       pmd_t *pmd;
+       pte_t *pte;
+       spinlock_t *ptl;
+       unsigned int flags;
+};
+
+static inline void page_vma_mapped_walk_done(struct page_vma_mapped_walk *pvmw)
+{
+       if (pvmw->pte)
+               pte_unmap(pvmw->pte);
+       if (pvmw->ptl)
+               spin_unlock(pvmw->ptl);
+}
+
+bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw);
+
 /*
  * Used by swapoff to help locate where page is expected in vma.
  */

diff --git a/mm/Makefile b/mm/Makefile
index 433eaf9a876ed71b06a588a7fb08b28ce4254717..aa0aa17cb413ad223bac0fff88c15ec8ee3f8dd9 100644 (file)
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -23,8 +23,10 @@ KCOV_INSTRUMENT_vmstat.o := n
 
 mmu-y                  := nommu.o
 mmu-$(CONFIG_MMU)      := gup.o highmem.o memory.o mincore.o \
-                          mlock.o mmap.o mprotect.o mremap.o msync.o rmap.o \
-                          vmalloc.o pagewalk.o pgtable-generic.o
+                          mlock.o mmap.o mprotect.o mremap.o msync.o \
+                          page_vma_mapped.o pagewalk.o pgtable-generic.o \
+                          rmap.o vmalloc.o
+
 
 ifdef CONFIG_CROSS_MEMORY_ATTACH
 mmu-$(CONFIG_MMU)      += process_vm_access.o

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 85742ac5b32ea6f72cfdb229c1ee843dc823d8fb..a7bac4f2b78aa62e750f6282dd6215b54a983dd3 100644 (file)
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2129,9 +2129,12 @@ static void freeze_page(struct page *page)
 static void unfreeze_page(struct page *page)
 {
        int i;
-
-       for (i = 0; i < HPAGE_PMD_NR; i++)
-               remove_migration_ptes(page + i, page + i, true);
+       if (PageTransHuge(page)) {
+               remove_migration_ptes(page, page, true);
+       } else {
+               for (i = 0; i < HPAGE_PMD_NR; i++)
+                       remove_migration_ptes(page + i, page + i, true);
+       }
 }
 
 static void __split_huge_page_tail(struct page *head, int tail,

diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
new file mode 100644 (file)
index 0000000..dc1a548
--- /dev/null
+++ b/mm/page_vma_mapped.c
@@ -0,0 +1,188 @@
+#include <linux/mm.h>
+#include <linux/rmap.h>
+#include <linux/hugetlb.h>
+#include <linux/swap.h>
+#include <linux/swapops.h>
+
+#include "internal.h"
+
+static inline bool check_pmd(struct page_vma_mapped_walk *pvmw)
+{
+       pmd_t pmde;
+       /*
+        * Make sure we don't re-load pmd between present and !trans_huge check.
+        * We need a consistent view.
+        */
+       pmde = READ_ONCE(*pvmw->pmd);
+       return pmd_present(pmde) && !pmd_trans_huge(pmde);
+}
+
+static inline bool not_found(struct page_vma_mapped_walk *pvmw)
+{
+       page_vma_mapped_walk_done(pvmw);
+       return false;
+}
+
+static bool map_pte(struct page_vma_mapped_walk *pvmw)
+{
+       pvmw->pte = pte_offset_map(pvmw->pmd, pvmw->address);
+       if (!(pvmw->flags & PVMW_SYNC)) {
+               if (pvmw->flags & PVMW_MIGRATION) {
+                       if (!is_swap_pte(*pvmw->pte))
+                               return false;
+               } else {
+                       if (!pte_present(*pvmw->pte))
+                               return false;
+               }
+       }
+       pvmw->ptl = pte_lockptr(pvmw->vma->vm_mm, pvmw->pmd);
+       spin_lock(pvmw->ptl);
+       return true;
+}
+
+static bool check_pte(struct page_vma_mapped_walk *pvmw)
+{
+       if (pvmw->flags & PVMW_MIGRATION) {
+#ifdef CONFIG_MIGRATION
+               swp_entry_t entry;
+               if (!is_swap_pte(*pvmw->pte))
+                       return false;
+               entry = pte_to_swp_entry(*pvmw->pte);
+               if (!is_migration_entry(entry))
+                       return false;
+               if (migration_entry_to_page(entry) - pvmw->page >=
+                               hpage_nr_pages(pvmw->page)) {
+                       return false;
+               }
+               if (migration_entry_to_page(entry) < pvmw->page)
+                       return false;
+#else
+               WARN_ON_ONCE(1);
+#endif
+       } else {
+               if (!pte_present(*pvmw->pte))
+                       return false;
+
+               /* THP can be referenced by any subpage */
+               if (pte_page(*pvmw->pte) - pvmw->page >=
+                               hpage_nr_pages(pvmw->page)) {
+                       return false;
+               }
+               if (pte_page(*pvmw->pte) < pvmw->page)
+                       return false;
+       }
+
+       return true;
+}
+
+/**
+ * page_vma_mapped_walk - check if @pvmw->page is mapped in @pvmw->vma at
+ * @pvmw->address
+ * @pvmw: pointer to struct page_vma_mapped_walk. page, vma, address and flags
+ * must be set. pmd, pte and ptl must be NULL.
+ *
+ * Returns true if the page is mapped in the vma. @pvmw->pmd and @pvmw->pte point
+ * to relevant page table entries. @pvmw->ptl is locked. @pvmw->address is
+ * adjusted if needed (for PTE-mapped THPs).
+ *
+ * If @pvmw->pmd is set but @pvmw->pte is not, you have found PMD-mapped page
+ * (usually THP). For PTE-mapped THP, you should run page_vma_mapped_walk() in
+ * a loop to find all PTEs that map the THP.
+ *
+ * For HugeTLB pages, @pvmw->pte is set to the relevant page table entry
+ * regardless of which page table level the page is mapped at. @pvmw->pmd is
+ * NULL.
+ *
+ * Retruns false if there are no more page table entries for the page in
+ * the vma. @pvmw->ptl is unlocked and @pvmw->pte is unmapped.
+ *
+ * If you need to stop the walk before page_vma_mapped_walk() returned false,
+ * use page_vma_mapped_walk_done(). It will do the housekeeping.
+ */
+bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
+{
+       struct mm_struct *mm = pvmw->vma->vm_mm;
+       struct page *page = pvmw->page;
+       pgd_t *pgd;
+       pud_t *pud;
+
+       /* The only possible pmd mapping has been handled on last iteration */
+       if (pvmw->pmd && !pvmw->pte)
+               return not_found(pvmw);
+
+       /* Only for THP, seek to next pte entry makes sense */
+       if (pvmw->pte) {
+               if (!PageTransHuge(pvmw->page) || PageHuge(pvmw->page))
+                       return not_found(pvmw);
+               goto next_pte;
+       }
+
+       if (unlikely(PageHuge(pvmw->page))) {
+               /* when pud is not present, pte will be NULL */
+               pvmw->pte = huge_pte_offset(mm, pvmw->address);
+               if (!pvmw->pte)
+                       return false;
+
+               pvmw->ptl = huge_pte_lockptr(page_hstate(page), mm, pvmw->pte);
+               spin_lock(pvmw->ptl);
+               if (!check_pte(pvmw))
+                       return not_found(pvmw);
+               return true;
+       }
+restart:
+       pgd = pgd_offset(mm, pvmw->address);
+       if (!pgd_present(*pgd))
+               return false;
+       pud = pud_offset(pgd, pvmw->address);
+       if (!pud_present(*pud))
+               return false;
+       pvmw->pmd = pmd_offset(pud, pvmw->address);
+       if (pmd_trans_huge(*pvmw->pmd)) {
+               pvmw->ptl = pmd_lock(mm, pvmw->pmd);
+               if (!pmd_present(*pvmw->pmd))
+                       return not_found(pvmw);
+               if (likely(pmd_trans_huge(*pvmw->pmd))) {
+                       if (pvmw->flags & PVMW_MIGRATION)
+                               return not_found(pvmw);
+                       if (pmd_page(*pvmw->pmd) != page)
+                               return not_found(pvmw);
+                       return true;
+               } else {
+                       /* THP pmd was split under us: handle on pte level */
+                       spin_unlock(pvmw->ptl);
+                       pvmw->ptl = NULL;
+               }
+       } else {
+               if (!check_pmd(pvmw))
+                       return false;
+       }
+       if (!map_pte(pvmw))
+               goto next_pte;
+       while (1) {
+               if (check_pte(pvmw))
+                       return true;
+next_pte:      do {
+                       pvmw->address += PAGE_SIZE;
+                       if (pvmw->address >=
+                                       __vma_address(pvmw->page, pvmw->vma) +
+                                       hpage_nr_pages(pvmw->page) * PAGE_SIZE)
+                               return not_found(pvmw);
+                       /* Did we cross page table boundary? */
+                       if (pvmw->address % PMD_SIZE == 0) {
+                               pte_unmap(pvmw->pte);
+                               if (pvmw->ptl) {
+                                       spin_unlock(pvmw->ptl);
+                                       pvmw->ptl = NULL;
+                               }
+                               goto restart;
+                       } else {
+                               pvmw->pte++;
+                       }
+               } while (pte_none(*pvmw->pte));
+
+               if (!pvmw->ptl) {
+                       pvmw->ptl = pte_lockptr(mm, pvmw->pmd);
+                       spin_lock(pvmw->ptl);
+               }
+       }
+}