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authorLinus Torvalds <torvalds@linux-foundation.org>2010-02-26 17:05:10 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2010-02-26 17:05:10 -0800
commitf24407d2bde27a4eb75ce5e52069bf4f1ba0e8a5 (patch)
tree6ad6dbc0b3d394435615b5e53b7d2ab3bde4c354 /Documentation
parent654451748b779b28077d9058442d0f354251870d (diff)
parent73c77e2ccc14413c232c3e0b3aa43a0c4b72ec70 (diff)
Merge git://git.kernel.org/pub/scm/linux/kernel/git/jejb/xfs-vipt
* git://git.kernel.org/pub/scm/linux/kernel/git/jejb/xfs-vipt: xfs: fix xfs to work with Virtually Indexed architectures sh: add mm API for DMA to vmalloc/vmap areas arm: add mm API for DMA to vmalloc/vmap areas parisc: add mm API for DMA to vmalloc/vmap areas mm: add coherence API for DMA to vmalloc/vmap areas
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/cachetlb.txt24
1 files changed, 24 insertions, 0 deletions
diff --git a/Documentation/cachetlb.txt b/Documentation/cachetlb.txt
index da42ab414c4..b231414bb8b 100644
--- a/Documentation/cachetlb.txt
+++ b/Documentation/cachetlb.txt
@@ -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.
+
+The final category of APIs is for I/O to deliberately aliased address
+ranges inside the kernel. Such aliases are set up by use of the
+vmap/vmalloc API. Since kernel I/O goes via physical pages, the I/O
+subsystem assumes that the user mapping and kernel offset mapping are
+the only aliases. This isn't true for vmap aliases, so anything in
+the kernel trying to do I/O to vmap areas must manually manage
+coherency. It must do this by flushing the vmap range before doing
+I/O and invalidating it after the I/O returns.
+
+ void flush_kernel_vmap_range(void *vaddr, int size)
+ flushes the kernel cache for a given virtual address range in
+ the vmap area. This is to make sure that any data the kernel
+ modified in the vmap range is made visible to the physical
+ page. The design is to make this area safe to perform I/O on.
+ Note that this API does *not* also flush the offset map alias
+ of the area.
+
+ void invalidate_kernel_vmap_range(void *vaddr, int size) invalidates
+ the cache for a given virtual address range in the vmap area
+ which prevents the processor from making the cache stale by
+ speculatively reading data while the I/O was occurring to the
+ physical pages. This is only necessary for data reads into the
+ vmap area.