[PATCH 2/2] add flush_kernel_dcache_page() API

From: James Bottomley
Date: Tue Mar 21 2006 - 14:43:00 EST

We have a problem in a lot of emulated storage in that it takes a page
from get_user_pages() and does something like

modify page

However, nothing has flushed the kernel cache view of the page before
the kunmap. We need a lightweight API to do this, so this new API
would specifically be for flushing the kernel cache view of a user
page which the kernel has modified. The driver would need to add
flush_kernel_dcache_page(page) before the final kunmap.

Signed-off-by: James Bottomley <James.Bottomley@xxxxxxxxxxxx>

Index: BUILD-2.6/Documentation/cachetlb.txt
--- BUILD-2.6.orig/Documentation/cachetlb.txt 2006-03-21 13:37:45.000000000 -0600
+++ BUILD-2.6/Documentation/cachetlb.txt 2006-03-21 13:37:54.000000000 -0600
@@ -371,6 +371,18 @@
architectures). For incoherent architectures, it should flush
the cache of the page at vmaddr in the current user process.

+ void flush_kernel_dcache_page(struct page *page)
+ When the kernel needs to modify a user page is has obtained
+ with kmap, it calls this function after all modifications are
+ complete (but before kunmapping it) to bring the underlying
+ page up to date. It is assumed here that the user has no
+ incoherent cached copies (i.e. the original page was obtained
+ from a mechanism like get_user_pages()). The default
+ implementation is a nop and should remain so on all coherent
+ architectures. On incoherent architectures, this should flush
+ the kernel cache for page (using page_address(page)).
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 2006-03-21 13:37:19.000000000 -0600
+++ BUILD-2.6/include/linux/highmem.h 2006-03-21 13:37:54.000000000 -0600
@@ -13,6 +13,12 @@

+static inline void flush_kernel_dcache_page(struct page *page)

#include <asm/highmem.h>

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