[Xen-devel] [PATCH 1/9] mm: Introduce new vm_insert_range and vm_insert_range_buggy API

[Souptick Joarder <jrdr.linux@xxxxxxxxx>]

Previouly drivers have their own way of mapping range of
kernel pages/memory into user vma and this was done by
invoking vm_insert_page() within a loop.

As this pattern is common across different drivers, it can
be generalized by creating new functions and use it across
the drivers.

vm_insert_range() is the API which could be used to mapped
kernel memory/pages in drivers which has considered vm_pgoff

vm_insert_range_buggy() is the API which could be used to map
range of kernel memory/pages in drivers which has not considered
vm_pgoff. vm_pgoff is passed default as 0 for those drivers.

We _could_ then at a later "fix" these drivers which are using
vm_insert_range_buggy() to behave according to the normal vm_pgoff
offsetting simply by removing the _buggy suffix on the function
name and if that causes regressions, it gives us an easy way to revert.

Signed-off-by: Souptick Joarder <jrdr.linux@xxxxxxxxx>
Suggested-by: Russell King <linux@xxxxxxxxxxxxxxx>
Suggested-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
---
 include/linux/mm.h |  4 +++
 mm/memory.c        | 81 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 mm/nommu.c         | 14 ++++++++++
 3 files changed, 99 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 5411de9..9d1dff6 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2514,6 +2514,10 @@ unsigned long change_prot_numa(struct vm_area_struct 
*vma,
 int remap_pfn_range(struct vm_area_struct *, unsigned long addr,
                        unsigned long pfn, unsigned long size, pgprot_t);
 int vm_insert_page(struct vm_area_struct *, unsigned long addr, struct page *);
+int vm_insert_range(struct vm_area_struct *vma, struct page **pages,
+                               unsigned long num);
+int vm_insert_range_buggy(struct vm_area_struct *vma, struct page **pages,
+                               unsigned long num);
 vm_fault_t vmf_insert_pfn(struct vm_area_struct *vma, unsigned long addr,
                        unsigned long pfn);
 vm_fault_t vmf_insert_pfn_prot(struct vm_area_struct *vma, unsigned long addr,
diff --git a/mm/memory.c b/mm/memory.c
index 4ad2d29..00e66df 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1520,6 +1520,87 @@ int vm_insert_page(struct vm_area_struct *vma, unsigned 
long addr,
 }
 EXPORT_SYMBOL(vm_insert_page);
 
+/**
+ * __vm_insert_range - insert range of kernel pages into user vma
+ * @vma: user vma to map to
+ * @pages: pointer to array of source kernel pages
+ * @num: number of pages in page array
+ * @offset: user's requested vm_pgoff
+ *
+ * This allows drivers to insert range of kernel pages they've allocated
+ * into a user vma.
+ *
+ * If we fail to insert any page into the vma, the function will return
+ * immediately leaving any previously inserted pages present.  Callers
+ * from the mmap handler may immediately return the error as their caller
+ * will destroy the vma, removing any successfully inserted pages. Other
+ * callers should make their own arrangements for calling unmap_region().
+ *
+ * Context: Process context.
+ * Return: 0 on success and error code otherwise.
+ */
+static int __vm_insert_range(struct vm_area_struct *vma, struct page **pages,
+                               unsigned long num, unsigned long offset)
+{
+       unsigned long count = vma_pages(vma);
+       unsigned long uaddr = vma->vm_start;
+       int ret, i;
+
+       /* Fail if the user requested offset is beyond the end of the object */
+       if (offset > num)
+               return -ENXIO;
+
+       /* Fail if the user requested size exceeds available object size */
+       if (count > num - offset)
+               return -ENXIO;
+
+       for (i = 0; i < count; i++) {
+               ret = vm_insert_page(vma, uaddr, pages[offset + i]);
+               if (ret < 0)
+                       return ret;
+               uaddr += PAGE_SIZE;
+       }
+
+       return 0;
+}
+
+/**
+ * vm_insert_range - insert range of kernel pages starts with non zero offset
+ * @vma: user vma to map to
+ * @pages: pointer to array of source kernel pages
+ * @num: number of pages in page array
+ *
+ * Maps an object consisting of `num' `pages', catering for the user's
+ * requested vm_pgoff
+ *
+ * Context: Process context. Called by mmap handlers.
+ * Return: 0 on success and error code otherwise.
+ */
+int vm_insert_range(struct vm_area_struct *vma, struct page **pages,
+                               unsigned long num)
+{
+       return __vm_insert_range(vma, pages, num, vma->vm_pgoff);
+}
+EXPORT_SYMBOL(vm_insert_range);
+
+/**
+ * vm_insert_range_buggy - insert range of kernel pages starts with zero offset
+ * @vma: user vma to map to
+ * @pages: pointer to array of source kernel pages
+ * @num: number of pages in page array
+ *
+ * Maps a set of pages, always starting at page[0]
+ *
+ * Context: Process context. Called by mmap handlers.
+ * Return: 0 on success and error code otherwise.
+ */
+int vm_insert_range_buggy(struct vm_area_struct *vma, struct page **pages,
+                               unsigned long num)
+{
+       return __vm_insert_range(vma, pages, num, 0);
+}
+EXPORT_SYMBOL(vm_insert_range_buggy);
+
 static vm_fault_t insert_pfn(struct vm_area_struct *vma, unsigned long addr,
                        pfn_t pfn, pgprot_t prot, bool mkwrite)
 {
diff --git a/mm/nommu.c b/mm/nommu.c
index 749276b..21d101e 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -473,6 +473,20 @@ int vm_insert_page(struct vm_area_struct *vma, unsigned 
long addr,
 }
 EXPORT_SYMBOL(vm_insert_page);
 
+int vm_insert_range(struct vm_area_struct *vma, struct page **pages,
+                       unsigned long num)
+{
+       return -EINVAL;
+}
+EXPORT_SYMBOL(vm_insert_range);
+
+int vm_insert_range_buggy(struct vm_area_struct *vma, struct page **pages,
+                               unsigned long num)
+{
+       return -EINVAL;
+}
+EXPORT_SYMBOL(vm_insert_range_buggy);
+
 /*
  *  sys_brk() for the most part doesn't need the global kernel
  *  lock, except when an application is doing something nasty
-- 
1.9.1


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