[Xen-devel] [RFC PATCH 30/35] Add generic_page_range() function

[Chris Wright <chrisw@xxxxxxxxxxxx>]

Add a new mm function generic_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()).

Signed-off-by: Ian Pratt <ian.pratt@xxxxxxxxxxxxx>
Signed-off-by: Christian Limpach <Christian.Limpach@xxxxxxxxxxxx>
Signed-off-by: Chris Wright <chrisw@xxxxxxxxxxxx>
---
 include/linux/mm.h |    5 ++
 mm/memory.c        |   90 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 95 insertions(+)

--- xen-subarch-2.6.orig/include/linux/mm.h
+++ xen-subarch-2.6/include/linux/mm.h
@@ -1013,6 +1013,11 @@ struct page *follow_page(struct vm_area_
 #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 *pte_page, unsigned long addr,
+                        void *data);
+extern int generic_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
--- xen-subarch-2.6.orig/mm/memory.c
+++ xen-subarch-2.6/mm/memory.c
@@ -1359,6 +1359,96 @@ int remap_pfn_range(struct vm_area_struc
 }
 EXPORT_SYMBOL(remap_pfn_range);
 
+static inline int generic_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 *pte_page;
+
+       pte = (mm == &init_mm) ?
+               pte_alloc_kernel(pmd, addr) :
+               pte_alloc_map(mm, pmd, addr);
+       if (!pte)
+               return -ENOMEM;
+
+       pte_page = pmd_page(*pmd);
+
+       do {
+               err = fn(pte, pte_page, addr, data);
+               if (err)
+                       break;
+       } while (pte++, addr += PAGE_SIZE, addr != end);
+
+       if (mm != &init_mm)
+               pte_unmap(pte-1);
+       return err;
+}
+
+static inline int generic_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 = generic_pte_range(mm, pmd, addr, next, fn, data);
+               if (err)
+                       break;
+       } while (pmd++, addr = next, addr != end);
+       return err;
+}
+
+static inline int generic_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 = generic_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 generic_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 = generic_pud_range(mm, pgd, addr, next, fn, data);
+               if (err)
+                       break;
+       } while (pgd++, addr = next, addr != end);
+       return err;
+}
+
 /*
  * handle_pte_fault chooses page fault handler according to an entry
  * which was read non-atomically.  Before making any commitment, on

--

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