On Thu, 2011-01-06 at 12:25 -0600, James Bottomley wrote:

OK, so thinking about this, it seems that the only danger is actually
what NFS is doing: reading cache pages via a vmap.  In that case, since
the requirement is to invalidate the vmap range to prepare for read, we
could have invalidate_kernel_vmap_range loop over the underlying pages
and flush them through the kernel alias if the architecture specific
flag indicates their contents might be dirty.

The loop adds expense that is probably largely unnecessary to
invalidate_kernel_vmap_range() but the alternative is adding to the API
proliferation with something that only flushes the kernel pages if the
arch specific flag says they're dirty.

This is what I think the arm patch would look like (example only: I
can't compile it).  Is something like this too expensive? the loop can't
be optimised away because of the need to check the pages (and
vmalloc_to_page is a three level page table lookup).

James

---

diff --git a/arch/arm/include/asm/cacheflush.h b/arch/arm/include/asm/cacheflush.h
index 3acd8fa..34469ca 100644
--- a/arch/arm/include/asm/cacheflush.h
+++ b/arch/arm/include/asm/cacheflush.h

@@ -414,8 +414,17 @@ static inline void flush_kernel_vmap_range(void *addr, int size)
 }
 static inline void invalidate_kernel_vmap_range(void *addr, int size)
 {
-	if ((cache_is_vivt() || cache_is_vipt_aliasing()))
-	  __cpuc_flush_dcache_area(addr, (size_t)size);
+	if ((cache_is_vivt() || cache_is_vipt_aliasing())) {
+		void *cursor = addr;
+
+		for ( ; cursor < addr + size; cursor += PAGE_SIZE) {
+			struct page *page = vmalloc_to_page(cursor);
+
+			if (!test_and_set_bit(PG_dcache_clean, &page->flags))
+				__flush_dcache_page(page_mapping(page), page);
+		}
+		__cpuc_flush_dcache_area(addr, (size_t)size);
+	}
 }
 
 #define ARCH_HAS_FLUSH_ANON_PAGE