VM: add "vm_insert_page()" function
This is what a lot of drivers will actually want to use to insert
individual pages into a user VMA. It doesn't have the old PageReserved
restrictions of remap_pfn_range(), and it doesn't complain about partial
remappings.
The page you insert needs to be a nice clean kernel allocation, so you
can't insert arbitrary page mappings with this, but that's not what
people want.
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 0e73f15..29f02d8 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -956,6 +956,7 @@
unsigned long vmalloc_to_pfn(void *addr);
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 *);
struct page *follow_page(struct vm_area_struct *, unsigned long address,
unsigned int foll_flags);
diff --git a/mm/memory.c b/mm/memory.c
index 8d10b55..4b4fc3a 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1172,7 +1172,7 @@
spinlock_t *ptl;
retval = -EINVAL;
- if (PageAnon(page) || !PageReserved(page))
+ if (PageAnon(page))
goto out;
retval = -ENOMEM;
flush_dcache_page(page);
@@ -1197,6 +1197,35 @@
}
/*
+ * This allows drivers to insert individual pages they've allocated
+ * into a user vma.
+ *
+ * The page has to be a nice clean _individual_ kernel allocation.
+ * If you allocate a compound page, you need to have marked it as
+ * such (__GFP_COMP), or manually just split the page up yourself
+ * (which is mainly an issue of doing "set_page_count(page, 1)" for
+ * each sub-page, and then freeing them one by one when you free
+ * them rather than freeing it as a compound page).
+ *
+ * NOTE! Traditionally this was done with "remap_pfn_range()" which
+ * took an arbitrary page protection parameter. This doesn't allow
+ * that. Your vma protection will have to be set up correctly, which
+ * means that if you want a shared writable mapping, you'd better
+ * ask for a shared writable mapping!
+ *
+ * The page does not need to be reserved.
+ */
+int vm_insert_page(struct vm_area_struct *vma, unsigned long addr, struct page *page)
+{
+ if (addr < vma->vm_start || addr >= vma->vm_end)
+ return -EFAULT;
+ if (!page_count(page))
+ return -EINVAL;
+ return insert_page(vma->vm_mm, addr, page, vma->vm_page_prot);
+}
+EXPORT_SYMBOL_GPL(vm_insert_page);
+
+/*
* Somebody does a pfn remapping that doesn't actually work as a vma.
*
* Do it as individual pages instead, and warn about it. It's bad form,
@@ -1225,8 +1254,11 @@
if (!pfn_valid(pfn))
return -EINVAL;
- retval = 0;
page = pfn_to_page(pfn);
+ if (!PageReserved(page))
+ return -EINVAL;
+
+ retval = 0;
while (start < end) {
retval = insert_page(vma->vm_mm, start, page, prot);
if (retval < 0)