Add apply_to_page_range() which applies a function to a pte range

Add a new mm function apply_to_page_range() which applies a given function to
every pte in a given virtual address range in a given mm structure.  This is a
generic alternative to cut-and-pasting the Linux idiomatic pagetable walking
code in every place that a sequence of PTEs must be accessed.

Although this interface is intended to be useful in a wide range of
situations, it is currently used specifically by several Xen subsystems, for
example: to ensure that pagetables have been allocated for a virtual address
range, and to construct batched special pagetable update requests to map I/O
memory (in ioremap()).

[akpm@linux-foundation.org: fix warning, unpleasantly]
Signed-off-by: Ian Pratt <ian.pratt@xensource.com>
Signed-off-by: Christian Limpach <Christian.Limpach@cl.cam.ac.uk>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Cc: Christoph Lameter <clameter@sgi.com>
Cc: Matt Mackall <mpm@waste.org>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 99 insertions, 0 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 60e0e4a592d2..7bf0bd882fc3 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1130,6 +1130,11 @@ struct page *follow_page(struct vm_area_struct *, unsigned long address,
 #define FOLL_GET        0x04    /* do get_page on page */
 #define FOLL_ANON       0x08    /* give ZERO_PAGE if no pgtable */
 
+typedef int (*pte_fn_t)(pte_t *pte, struct page *pmd_page, unsigned long addr,
+                        void *data);
+extern int apply_to_page_range(struct mm_struct *mm, unsigned long address,
+                               unsigned long size, pte_fn_t fn, void *data);
+
 #ifdef CONFIG_PROC_FS
 void vm_stat_account(struct mm_struct *, unsigned long, struct file *, long);
 #else
diff --git a/mm/memory.c b/mm/memory.c
index e7066e71dfa3..044feb7e7134 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1448,6 +1448,100 @@ int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
 }
 EXPORT_SYMBOL(remap_pfn_range);
 
+static int apply_to_pte_range(struct mm_struct *mm, pmd_t *pmd,
+                                     unsigned long addr, unsigned long end,
+                                     pte_fn_t fn, void *data)
+{
+        pte_t *pte;
+        int err;
+        struct page *pmd_page;
+        spinlock_t *ptl = ptl;          /* Suppress gcc warning */
+
+        pte = (mm == &init_mm) ?
+                pte_alloc_kernel(pmd, addr) :
+                pte_alloc_map_lock(mm, pmd, addr, &ptl);
+        if (!pte)
+                return -ENOMEM;
+
+        BUG_ON(pmd_huge(*pmd));
+
+        pmd_page = pmd_page(*pmd);
+
+        do {
+                err = fn(pte, pmd_page, addr, data);
+                if (err)
+                        break;
+        } while (pte++, addr += PAGE_SIZE, addr != end);
+
+        if (mm != &init_mm)
+                pte_unmap_unlock(pte-1, ptl);
+        return err;
+}
+
+static int apply_to_pmd_range(struct mm_struct *mm, pud_t *pud,
+                                     unsigned long addr, unsigned long end,
+                                     pte_fn_t fn, void *data)
+{
+        pmd_t *pmd;
+        unsigned long next;
+        int err;
+
+        pmd = pmd_alloc(mm, pud, addr);
+        if (!pmd)
+                return -ENOMEM;
+        do {
+                next = pmd_addr_end(addr, end);
+                err = apply_to_pte_range(mm, pmd, addr, next, fn, data);
+                if (err)
+                        break;
+        } while (pmd++, addr = next, addr != end);
+        return err;
+}
+
+static int apply_to_pud_range(struct mm_struct *mm, pgd_t *pgd,
+                                     unsigned long addr, unsigned long end,
+                                     pte_fn_t fn, void *data)
+{
+        pud_t *pud;
+        unsigned long next;
+        int err;
+
+        pud = pud_alloc(mm, pgd, addr);
+        if (!pud)
+                return -ENOMEM;
+        do {
+                next = pud_addr_end(addr, end);
+                err = apply_to_pmd_range(mm, pud, addr, next, fn, data);
+                if (err)
+                        break;
+        } while (pud++, addr = next, addr != end);
+        return err;
+}
+
+/*
+ * Scan a region of virtual memory, filling in page tables as necessary
+ * and calling a provided function on each leaf page table.
+ */
+int apply_to_page_range(struct mm_struct *mm, unsigned long addr,
+                        unsigned long size, pte_fn_t fn, void *data)
+{
+        pgd_t *pgd;
+        unsigned long next;
+        unsigned long end = addr + size;
+        int err;
+
+        BUG_ON(addr >= end);
+        pgd = pgd_offset(mm, addr);
+        do {
+                next = pgd_addr_end(addr, end);
+                err = apply_to_pud_range(mm, pgd, addr, next, fn, data);
+                if (err)
+                        break;
+        } while (pgd++, addr = next, addr != end);
+        return err;
+}
+EXPORT_SYMBOL_GPL(apply_to_page_range);
+
 /*
  * handle_pte_fault chooses page fault handler according to an entry
  * which was read non-atomically.  Before making any commitment, on