@@ -377,3 +377,27 @@ maps this page at its virtual address.
All the functionality of flush_icache_page can be implemented in
flush_dcache_page and update_mmu_cache. In 2.7 the hope is to
remove this interface completely.
+
+For machines where aliasing can be a problem, there exist two
+additional APIs to handle I/O to vmap/vmalloc areas within the
+kernel. These are areas that have two kernel mappings, one the regular
+page offset map through which the page has likely been previously
+accessed and the other, the new contiguous map in the kernel virtual
+map area. This dual mapping sets up aliasing within the kernel and,
+in particular since all kernel flushing goes through the offset map,
+must be handled separately for I/O. to declare your architecture as
+needing to use these functions, you must define
+ARCH_HAS_FLUSH_KERNEL_DCACHE_PAGE in asm/cacheflush.h and add two API
+helpers (usually as static inlines in cacheflush.h). The two new APIs
+are:
+
+ void flush_kernel_dcache_addr(void *addr)
+ Flush a single page through the vmap alias for addr. This is
+ usually executed prior to performing I/O on the page to make
+ sure the underlying physical page is up to date.
+
+ void invalidate_kernel_dcache_addr(void *addr)
+ Invalidate the page after I/O has completed. This is necessary
+ on machines whose cache mechanisms might trigger cache movein
+ during I/O. If you can ensure architecturally that this movein
+ never occurs, this function can be empty on your architecture.