[RESEND PATCH] ARM: Handle user space mapped pages in flush_kernel_dcache_page

[Simon Baatz]

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>
---

Hi,

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
original post)

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.

- Simon


 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
--- a/arch/arm/include/asm/cacheflush.h
+++ b/arch/arm/include/asm/cacheflush.h
@@ -303,6 +303,10 @@ static inline void flush_anon_page(struct vm_area_struct *vma,
 #define ARCH_HAS_FLUSH_KERNEL_DCACHE_PAGE
 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))
+		__flush_kernel_dcache_page(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
--- a/arch/arm/mm/flush.c
+++ b/arch/arm/mm/flush.c
@@ -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);
+}
+EXPORT_SYMBOL(__flush_kernel_dcache_page);
+
 static void __flush_dcache_aliases(struct address_space *mapping, struct page *page)
 {
 	struct mm_struct *mm = current->active_mm;
-- 
1.7.9.5