mm: pagewalk: add p4d_entry() and pgd_entry()

pgd_entry() and pud_entry() were removed by commit 0b1fbfe50006c410
("mm/pagewalk: remove pgd_entry() and pud_entry()") because there were no
users.  We're about to add users so reintroduce them, along with
p4d_entry() as we now have 5 levels of tables.

Note that commit a00cc7d9dd93d66a ("mm, x86: add support for PUD-sized
transparent hugepages") already re-added pud_entry() but with different
semantics to the other callbacks.  This commit reverts the semantics back
to match the other callbacks.

To support hmm.c which now uses the new semantics of pud_entry() a new
member ('action') of struct mm_walk is added which allows the callbacks to
either descend (ACTION_SUBTREE, the default), skip (ACTION_CONTINUE) or
repeat the callback (ACTION_AGAIN).  hmm.c is then updated to call
pud_trans_huge_lock() itself and make use of the splitting/retry logic of
the core code.

After this change pud_entry() is called for all entries, not just
transparent huge pages.

[arnd@arndb.de: fix unused variable warning]
Link: http://lkml.kernel.org/r/20200107204607.1533842-1-arnd@arndb.de
Link: http://lkml.kernel.org/r/20191218162402.45610-12-steven.price@arm.com
Change-Id: Iefcf3d5f987b2fcc64262da127543ae11207086c
Signed-off-by: Steven Price <steven.price@arm.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
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>
[backport of the commit 3afc423632a194d7d6afef34e4bb98f804cd071d from mainline]
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>

diff --git a/include/linux/pagewalk.h b/include/linux/pagewalk.h
index bddd975..ed30c86 100644 (file)
--- a/include/linux/pagewalk.h
+++ b/include/linux/pagewalk.h
@@ -8,15 +8,15 @@ struct mm_walk;
 
 /**
  * mm_walk_ops - callbacks for walk_page_range
- * @pud_entry:         if set, called for each non-empty PUD (2nd-level) entry
- *                     this handler should only handle pud_trans_huge() puds.
- *                     the pmd_entry or pte_entry callbacks will be used for
- *                     regular PUDs.
- * @pmd_entry:         if set, called for each non-empty PMD (3rd-level) entry
+ * @pgd_entry:         if set, called for each non-empty PGD (top-level) entry
+ * @p4d_entry:         if set, called for each non-empty P4D entry
+ * @pud_entry:         if set, called for each non-empty PUD entry
+ * @pmd_entry:         if set, called for each non-empty PMD entry
  *                     this handler is required to be able to handle
  *                     pmd_trans_huge() pmds.  They may simply choose to
  *                     split_huge_page() instead of handling it explicitly.
- * @pte_entry:         if set, called for each non-empty PTE (4th-level) entry
+ * @pte_entry:         if set, called for each non-empty PTE (lowest-level)
+ *                     entry
  * @pte_hole:          if set, called for each hole at all levels
  * @hugetlb_entry:     if set, called for each hugetlb entry
  * @test_walk:         caller specific callback function to determine whether
@@ -24,8 +24,15 @@ struct mm_walk;
  *                     "do page table walk over the current vma", returning
  *                     a negative value means "abort current page table walk
  *                     right now" and returning 1 means "skip the current vma"
+ *
+ * p?d_entry callbacks are called even if those levels are folded on a
+ * particular architecture/configuration.
  */
 struct mm_walk_ops {
+       int (*pgd_entry)(pgd_t *pgd, unsigned long addr,
+                        unsigned long next, struct mm_walk *walk);
+       int (*p4d_entry)(p4d_t *p4d, unsigned long addr,
+                        unsigned long next, struct mm_walk *walk);
        int (*pud_entry)(pud_t *pud, unsigned long addr,
                         unsigned long next, struct mm_walk *walk);
        int (*pmd_entry)(pmd_t *pmd, unsigned long addr,
@@ -41,11 +48,25 @@ struct mm_walk_ops {
                        struct mm_walk *walk);
 };
 
+/*
+ * Action for pud_entry / pmd_entry callbacks.
+ * ACTION_SUBTREE is the default
+ */
+enum page_walk_action {
+       /* Descend to next level, splitting huge pages if needed and possible */
+       ACTION_SUBTREE = 0,
+       /* Continue to next entry at this level (ignoring any subtree) */
+       ACTION_CONTINUE = 1,
+       /* Call again for this entry */
+       ACTION_AGAIN = 2
+};
+
 /**
  * mm_walk - walk_page_range data
  * @ops:       operation to call during the walk
  * @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)
  * @private:   private data for callbacks' usage
  *
  * (see the comment on walk_page_range() for more details)
@@ -54,6 +75,7 @@ struct mm_walk {
        const struct mm_walk_ops *ops;
        struct mm_struct *mm;
        struct vm_area_struct *vma;
+       enum page_walk_action action;
        void *private;
 };
 

diff --git a/mm/hmm.c b/mm/hmm.c
index 902f5fa..231de97 100644 (file)
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -658,23 +658,32 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end,
 {
        struct hmm_vma_walk *hmm_vma_walk = walk->private;
        struct hmm_range *range = hmm_vma_walk->range;
-       unsigned long addr = start, next;
-       pmd_t *pmdp;
+       unsigned long addr = start;
        pud_t pud;
-       int ret;
+       int ret = 0;
+       spinlock_t *ptl = pud_trans_huge_lock(pudp, walk->vma);
+
+       if (!ptl)
+               return 0;
+
+       /* Normally we don't want to split the huge page */
+       walk->action = ACTION_CONTINUE;
 
-again:
        pud = READ_ONCE(*pudp);
-       if (pud_none(pud))
-               return hmm_vma_walk_hole(start, end, walk);
+       if (pud_none(pud)) {
+               ret = hmm_vma_walk_hole(start, end, walk);
+               goto out_unlock;
+       }
 
        if (pud_huge(pud) && pud_devmap(pud)) {
                unsigned long i, npages, pfn;
                uint64_t *pfns, cpu_flags;
                bool fault, write_fault;
 
-               if (!pud_present(pud))
-                       return hmm_vma_walk_hole(start, end, walk);
+               if (!pud_present(pud)) {
+                       ret = hmm_vma_walk_hole(start, end, walk);
+                       goto out_unlock;
+               }
 
                i = (addr - range->start) >> PAGE_SHIFT;
                npages = (end - addr) >> PAGE_SHIFT;
@@ -683,16 +692,20 @@ again:
                cpu_flags = pud_to_hmm_pfn_flags(range, pud);
                hmm_range_need_fault(hmm_vma_walk, pfns, npages,
                                     cpu_flags, &fault, &write_fault);
-               if (fault || write_fault)
-                       return hmm_vma_walk_hole_(addr, end, fault,
-                                               write_fault, walk);
+               if (fault || write_fault) {
+                       ret = hmm_vma_walk_hole_(addr, end, fault,
+                                                write_fault, walk);
+                       goto out_unlock;
+               }
 
                pfn = pud_pfn(pud) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
                for (i = 0; i < npages; ++i, ++pfn) {
                        hmm_vma_walk->pgmap = get_dev_pagemap(pfn,
                                              hmm_vma_walk->pgmap);
-                       if (unlikely(!hmm_vma_walk->pgmap))
-                               return -EBUSY;
+                       if (unlikely(!hmm_vma_walk->pgmap)) {
+                               ret = -EBUSY;
+                               goto out_unlock;
+                       }
                        pfns[i] = hmm_device_entry_from_pfn(range, pfn) |
                                  cpu_flags;
                }
@@ -701,22 +714,15 @@ again:
                        hmm_vma_walk->pgmap = NULL;
                }
                hmm_vma_walk->last = end;
-               return 0;
+               goto out_unlock;
        }
 
-       split_huge_pud(walk->vma, pudp, addr);
-       if (pud_none(*pudp))
-               goto again;
+       /* Ask for the PUD to be split */
+       walk->action = ACTION_SUBTREE;
 
-       pmdp = pmd_offset(pudp, addr);
-       do {
-               next = pmd_addr_end(addr, end);
-               ret = hmm_vma_walk_pmd(pmdp, addr, next, walk);
-               if (ret)
-                       return ret;
-       } while (pmdp++, addr = next, addr != end);
-
-       return 0;
+out_unlock:
+       spin_unlock(ptl);
+       return ret;
 }
 #else
 #define hmm_vma_walk_pud       NULL

diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index d48c2a9..b36795d 100644 (file)
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -45,6 +45,9 @@ again:
                                break;
                        continue;
                }
+
+               walk->action = ACTION_SUBTREE;
+
                /*
                 * This implies that each ->pmd_entry() handler
                 * needs to know about pmd_trans_huge() pmds
@@ -54,16 +57,21 @@ again:
                if (err)
                        break;
 
+               if (walk->action == ACTION_AGAIN)
+                       goto again;
+
                /*
                 * Check this here so we only break down trans_huge
                 * pages when we _need_ to
                 */
-               if (!ops->pte_entry)
+               if (walk->action == ACTION_CONTINUE ||
+                   !(ops->pte_entry))
                        continue;
 
                split_huge_pmd(walk->vma, pmd, addr);
                if (pmd_trans_unstable(pmd))
                        goto again;
+
                err = walk_pte_range(pmd, addr, next, walk);
                if (err)
                        break;
@@ -92,24 +100,25 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,
                        continue;
                }
 
-               if (ops->pud_entry) {
-                       spinlock_t *ptl = pud_trans_huge_lock(pud, walk->vma);
+               walk->action = ACTION_SUBTREE;
 
-                       if (ptl) {
-                               err = ops->pud_entry(pud, addr, next, walk);
-                               spin_unlock(ptl);
-                               if (err)
-                                       break;
-                               continue;
-                       }
-               }
+               if (ops->pud_entry)
+                       err = ops->pud_entry(pud, addr, next, walk);
+               if (err)
+                       break;
+
+               if (walk->action == ACTION_AGAIN)
+                       goto again;
+
+               if (walk->action == ACTION_CONTINUE ||
+                   !(ops->pmd_entry || ops->pte_entry))
+                       continue;
 
                split_huge_pud(walk->vma, pud, addr);
                if (pud_none(*pud))
                        goto again;
 
-               if (ops->pmd_entry || ops->pte_entry)
-                       err = walk_pmd_range(pud, addr, next, walk);
+               err = walk_pmd_range(pud, addr, next, walk);
                if (err)
                        break;
        } while (pud++, addr = next, addr != end);
@@ -135,7 +144,12 @@ static int walk_p4d_range(pgd_t *pgd, unsigned long addr, unsigned long end,
                                break;
                        continue;
                }
-               if (ops->pmd_entry || ops->pte_entry)
+               if (ops->p4d_entry) {
+                       err = ops->p4d_entry(p4d, addr, next, walk);
+                       if (err)
+                               break;
+               }
+               if (ops->pud_entry || ops->pmd_entry || ops->pte_entry)
                        err = walk_pud_range(p4d, addr, next, walk);
                if (err)
                        break;
@@ -162,7 +176,13 @@ static int walk_pgd_range(unsigned long addr, unsigned long end,
                                break;
                        continue;
                }
-               if (ops->pmd_entry || ops->pte_entry)
+               if (ops->pgd_entry) {
+                       err = ops->pgd_entry(pgd, addr, next, walk);
+                       if (err)
+                               break;
+               }
+               if (ops->p4d_entry || ops->pud_entry || ops->pmd_entry ||
+                   ops->pte_entry)
                        err = walk_p4d_range(pgd, addr, next, walk);
                if (err)
                        break;