[PATCH] Add API for flushing Anon pages

Currently, get_user_pages() returns fully coherent pages to the kernel for
anything other than anonymous pages.  This is a problem for things like
fuse and the SCSI generic ioctl SG_IO which can potentially wish to do DMA
to anonymous pages passed in by users.

The fix is to add a new memory management API: flush_anon_page() which
is used in get_user_pages() to make anonymous pages coherent.

Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

3 files changed, 17 insertions, 0 deletions

diff --git a/Documentation/cachetlb.txt b/Documentation/cachetlb.txt
index 4ae418889b88..1f312a9893d9 100644
--- a/Documentation/cachetlb.txt
+++ b/Documentation/cachetlb.txt
@@ -362,6 +362,15 @@ maps this page at its virtual address.
         likely that you will need to flush the instruction cache
         for copy_to_user_page().
 
+  void flush_anon_page(struct page *page, unsigned long vmaddr)
+        When the kernel needs to access the contents of an anonymous
+        page, it calls this function (currently only
+        get_user_pages()).  Note: flush_dcache_page() deliberately
+        doesn't work for an anonymous page.  The default
+        implementation is a nop (and should remain so for all coherent
+        architectures).  For incoherent architectures, it should flush
+        the cache of the page at vmaddr in the current user process.
+
   void flush_icache_range(unsigned long start, unsigned long end)
         When the kernel stores into addresses that it will execute
         out of (eg when loading modules), this function is called.
diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index 6bece9280eb7..7bd2593dbef9 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -7,6 +7,12 @@
 
 #include <asm/cacheflush.h>
 
+#ifndef ARCH_HAS_FLUSH_ANON_PAGE
+static inline void flush_anon_page(struct page *page, unsigned long vmaddr)
+{
+}
+#endif
+
 #ifdef CONFIG_HIGHMEM
 
 #include <asm/highmem.h>
diff --git a/mm/memory.c b/mm/memory.c
index e347e106ca3a..67686048f094 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1071,6 +1071,8 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
                         }
                         if (pages) {
                                 pages[i] = page;
+
+                                flush_anon_page(page, start);
                                 flush_dcache_page(page);
                         }
                         if (vmas)