path: root/Documentation
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authorMatthew Wilcox <matthew.r.wilcox@intel.com>2015-02-16 15:59:44 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2015-02-16 17:56:04 -0800
commitd92576f1167cacf7844e5993f343eed4a6d8a147 (patch)
tree59bac8408c6faff4adb2d32398cff07b2e122b6b /Documentation
parenta7a97fc9ff6c2fcec00feb34d9b87b94452b0b78 (diff)
dax: does not work correctly with virtual aliasing caches
The DAX code accesses the underlying storage through the kernel's linear mapping, which may not be cache-coherent with user mappings on ARM, MIPS or SPARC. Temporarily disable the DAX code until this problem is resolved. The original XIP code also had this problem, but it was never noticed. Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com> Cc: Andreas Dilger <andreas.dilger@intel.com> Cc: Boaz Harrosh <boaz@plexistor.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Dave Chinner <david@fromorbit.com> Cc: Jan Kara <jack@suse.cz> Cc: Jens Axboe <axboe@kernel.dk> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Randy Dunlap <rdunlap@infradead.org> Cc: Ross Zwisler <ross.zwisler@linux.intel.com> Cc: Theodore Ts'o <tytso@mit.edu> Cc: Ralf Baechle <ralf@linux-mips.org> Cc: Russell King <rmk@arm.linux.org.uk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation')
1 files changed, 3 insertions, 0 deletions
diff --git a/Documentation/filesystems/dax.txt b/Documentation/filesystems/dax.txt
index be376d91d058..baf41118660d 100644
--- a/Documentation/filesystems/dax.txt
+++ b/Documentation/filesystems/dax.txt
@@ -82,6 +82,9 @@ Shortcomings
Even if the kernel or its modules are stored on a filesystem that supports
DAX on a block device that supports DAX, they will still be copied into RAM.
+The DAX code does not work correctly on architectures which have virtually
+mapped caches such as ARM, MIPS and SPARC.
Calling get_user_pages() on a range of user memory that has been mmaped
from a DAX file will fail as there are no 'struct page' to describe
those pages. This problem is being worked on. That means that O_DIRECT

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