[RESEND PATCH] ARM: Handle user space mapped pages in flush_kernel_dcache_page
gmbnomis at gmail.com
Sat Jul 28 04:41:54 EDT 2012
Commit f8b63c1 made flush_kernel_dcache_page a no-op assuming that the pages
it needs to handle are kernel mapped only. However, for example when doing
direct I/O, pages with user space mappings may occur.
Thus, continue to do lazy flushing if there are no user space mappings.
Otherwise, flush the kernel cache lines directly.
Signed-off-by: Simon Baatz <gmbnomis at gmail.com>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Russell King <linux at arm.linux.org.uk>
a while ago I sent the patch above to fix a data corruption problem
on VIVT architectures (and probably VIPT aliasing). There has been a
bit of discussion with Catalin, but there was no real conclusion on
how to proceed. (See
http://www.spinics.net/lists/arm-kernel/msg176913.html for the
The case is not hit too often apparently; the ingredients are PIO
(like) driver, use of flush_kernel_dcache_page(), and direct I/O.
However, there is at least one real world example (running lvm2 on
top of an encrypted block device using mv_cesa on Kirkwood) that does
not work at all because of this problem.
arch/arm/include/asm/cacheflush.h | 4 ++++
arch/arm/mm/flush.c | 22 ++++++++++++++++++++++
2 files changed, 26 insertions(+)
diff --git a/arch/arm/include/asm/cacheflush.h b/arch/arm/include/asm/cacheflush.h
index 004c1bc..91ddc70 100644
@@ -303,6 +303,10 @@ static inline void flush_anon_page(struct vm_area_struct *vma,
static inline void flush_kernel_dcache_page(struct page *page)
+ extern void __flush_kernel_dcache_page(struct page *);
+ /* highmem pages are always flushed upon kunmap already */
+ if ((cache_is_vivt() || cache_is_vipt_aliasing()) && !PageHighMem(page))
#define flush_dcache_mmap_lock(mapping) \
diff --git a/arch/arm/mm/flush.c b/arch/arm/mm/flush.c
index 7745854..bcba3a9 100644
@@ -192,6 +192,28 @@ void __flush_dcache_page(struct address_space *mapping, struct page *page)
page->index << PAGE_CACHE_SHIFT);
+ * Ensure cache coherency for kernel mapping of this page.
+ * If the page only exists in the page cache and there are no user
+ * space mappings, this is a no-op since the page was already marked
+ * dirty at creation. Otherwise, we need to flush the dirty kernel
+ * cache lines directly.
+ * We can assume that the page is no high mem page, see
+ * flush_kernel_dcache_page.
+void __flush_kernel_dcache_page(struct page *page)
+ struct address_space *mapping;
+ mapping = page_mapping(page);
+ if (!mapping || mapping_mapped(mapping))
+ __cpuc_flush_dcache_area(page_address(page), PAGE_SIZE);
static void __flush_dcache_aliases(struct address_space *mapping, struct page *page)
struct mm_struct *mm = current->active_mm;
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