mm: pagewalk: allow walking without vma

Since 48684a65b4e3: "mm: pagewalk: fix misbehavior of walk_page_range for
vma(VM_PFNMAP)", page_table_walk() will report any kernel area as a hole,
because it lacks a vma.

This means each arch has re-implemented page table walking when needed,
for example in the per-arch ptdump walker.

Remove the requirement to have a vma in the generic code and add a new
function walk_page_range_novma() which ignores the VMAs and simply walks
the page tables.

Link: http://lkml.kernel.org/r/20191218162402.45610-13-steven.price@arm.com
Signed-off-by: Steven Price <steven.price@arm.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexandre Ghiti <alex@ghiti.fr>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Hogan <jhogan@kernel.org>
Cc: James Morse <james.morse@arm.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: "Liang, Kan" <kan.liang@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Burton <paul.burton@mips.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: Will Deacon <will@kernel.org>
Cc: Zong Li <zong.li@sifive.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/pagewalk.h b/include/linux/pagewalk.h
index aa6a0b6..d5d07f7 100644 (file)
--- a/include/linux/pagewalk.h
+++ b/include/linux/pagewalk.h
@@ -73,6 +73,7 @@ enum page_walk_action {
  * @mm:                mm_struct representing the target process of page table walk
  * @vma:       vma currently walked (NULL if walking outside vmas)
  * @action:    next action to perform (see enum page_walk_action)
+ * @no_vma:    walk ignoring vmas (vma will always be NULL)
  * @private:   private data for callbacks' usage
  *
  * (see the comment on walk_page_range() for more details)
@@ -82,12 +83,16 @@ struct mm_walk {
        struct mm_struct *mm;
        struct vm_area_struct *vma;
        enum page_walk_action action;
+       bool no_vma;
        void *private;
 };
 
 int walk_page_range(struct mm_struct *mm, unsigned long start,
                unsigned long end, const struct mm_walk_ops *ops,
                void *private);
+int walk_page_range_novma(struct mm_struct *mm, unsigned long start,
+                         unsigned long end, const struct mm_walk_ops *ops,
+                         void *private);
 int walk_page_vma(struct vm_area_struct *vma, const struct mm_walk_ops *ops,
                void *private);
 int walk_page_mapping(struct address_space *mapping, pgoff_t first_index,

diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index 690af44..d577346 100644 (file)
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -39,7 +39,7 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,
        do {
 again:
                next = pmd_addr_end(addr, end);
-               if (pmd_none(*pmd) || !walk->vma) {
+               if (pmd_none(*pmd) || (!walk->vma && !walk->no_vma)) {
                        if (ops->pte_hole)
                                err = ops->pte_hole(addr, next, walk);
                        if (err)
@@ -65,13 +65,16 @@ again:
                 * Check this here so we only break down trans_huge
                 * pages when we _need_ to
                 */
-               if (walk->action == ACTION_CONTINUE ||
+               if ((!walk->vma && (pmd_leaf(*pmd) || !pmd_present(*pmd))) ||
+                   walk->action == ACTION_CONTINUE ||
                    !(ops->pte_entry))
                        continue;
 
-               split_huge_pmd(walk->vma, pmd, addr);
-               if (pmd_trans_unstable(pmd))
-                       goto again;
+               if (walk->vma) {
+                       split_huge_pmd(walk->vma, pmd, addr);
+                       if (pmd_trans_unstable(pmd))
+                               goto again;
+               }
 
                err = walk_pte_range(pmd, addr, next, walk);
                if (err)
@@ -93,7 +96,7 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,
        do {
  again:
                next = pud_addr_end(addr, end);
-               if (pud_none(*pud) || !walk->vma) {
+               if (pud_none(*pud) || (!walk->vma && !walk->no_vma)) {
                        if (ops->pte_hole)
                                err = ops->pte_hole(addr, next, walk);
                        if (err)
@@ -111,11 +114,13 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,
                if (walk->action == ACTION_AGAIN)
                        goto again;
 
-               if (walk->action == ACTION_CONTINUE ||
+               if ((!walk->vma && (pud_leaf(*pud) || !pud_present(*pud))) ||
+                   walk->action == ACTION_CONTINUE ||
                    !(ops->pmd_entry || ops->pte_entry))
                        continue;
 
-               split_huge_pud(walk->vma, pud, addr);
+               if (walk->vma)
+                       split_huge_pud(walk->vma, pud, addr);
                if (pud_none(*pud))
                        goto again;
 
@@ -389,6 +394,25 @@ int walk_page_range(struct mm_struct *mm, unsigned long start,
        return err;
 }
 
+int walk_page_range_novma(struct mm_struct *mm, unsigned long start,
+                         unsigned long end, const struct mm_walk_ops *ops,
+                         void *private)
+{
+       struct mm_walk walk = {
+               .ops            = ops,
+               .mm             = mm,
+               .private        = private,
+               .no_vma         = true
+       };
+
+       if (start >= end || !walk.mm)
+               return -EINVAL;
+
+       lockdep_assert_held(&walk.mm->mmap_sem);
+
+       return __walk_page_range(start, end, &walk);
+}
+
 int walk_page_vma(struct vm_area_struct *vma, const struct mm_walk_ops *ops,
                void *private)
 {