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 <[email protected]>
Index: BUILD-2.6/Documentation/cachetlb.txt
===================================================================
--- BUILD-2.6.orig/Documentation/cachetlb.txt 2006-03-20 10:44:45.000000000 -0600
+++ BUILD-2.6/Documentation/cachetlb.txt 2006-03-21 13:38:32.000000000 -0600
@@ -362,6 +362,15 @@
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.
Index: BUILD-2.6/include/linux/highmem.h
===================================================================
--- BUILD-2.6.orig/include/linux/highmem.h 2006-03-20 10:44:46.000000000 -0600
+++ BUILD-2.6/include/linux/highmem.h 2006-03-21 13:38:24.000000000 -0600
@@ -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>
Index: BUILD-2.6/mm/memory.c
===================================================================
--- BUILD-2.6.orig/mm/memory.c 2006-03-20 10:44:46.000000000 -0600
+++ BUILD-2.6/mm/memory.c 2006-03-20 10:44:55.000000000 -0600
@@ -1074,6 +1074,8 @@
}
if (pages) {
pages[i] = page;
+
+ flush_anon_page(page, start);
flush_dcache_page(page);
}
if (vmas)
-
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