diff options
| author | Dan Williams <dan.j.williams@intel.com> | 2017-10-14 20:33:32 +0200 |
|---|---|---|
| committer | Dan Williams <dan.j.williams@intel.com> | 2018-01-20 01:50:53 +0100 |
| commit | 569d0365f571fa6421a5c80bc30d1b2cdab857fe (patch) | |
| tree | 5f8be5e460e8d764a0481dda710e2131cdfb1991 /fs | |
| parent | ext2: auto disable dax instead of failing mount (diff) | |
| download | linux-569d0365f571fa6421a5c80bc30d1b2cdab857fe.tar.xz linux-569d0365f571fa6421a5c80bc30d1b2cdab857fe.zip | |
dax: require 'struct page' by default for filesystem dax
If a dax buffer from a device that does not map pages is passed to
read(2) or write(2) as a target for direct-I/O it triggers SIGBUS. If
gdb attempts to examine the contents of a dax buffer from a device that
does not map pages it triggers SIGBUS. If fork(2) is called on a process
with a dax mapping from a device that does not map pages it triggers
SIGBUS. 'struct page' is required otherwise several kernel code paths
break in surprising ways. Disable filesystem-dax on devices that do not
map pages.
In addition to needing pfn_to_page() to be valid we also require devmap
pages. We need this to detect dax pages in the get_user_pages_fast()
path and so that we can stop managing the VM_MIXEDMAP flag. For DAX
drivers that have not supported get_user_pages() to date we allow them
to opt-in to supporting DAX with the CONFIG_FS_DAX_LIMITED configuration
option which requires ->direct_access() to return pfn_t_special() pfns.
This leaves DAX support in brd disabled and scheduled for removal.
Note that when the initial dax support was being merged a few years back
there was concern that struct page was unsuitable for use with next
generation persistent memory devices. The theoretical concern was that
struct page access, being such a hotly used data structure in the
kernel, would lead to media wear out. While that was a reasonable
conservative starting position it has not held true in practice. We have
long since committed to using devm_memremap_pages() to support higher
order kernel functionality that needs get_user_pages() and
pfn_to_page().
Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/Kconfig | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/fs/Kconfig b/fs/Kconfig index 7aee6d699fd6..b40128bf6d1a 100644 --- a/fs/Kconfig +++ b/fs/Kconfig @@ -58,6 +58,13 @@ config FS_DAX_PMD depends on ZONE_DEVICE depends on TRANSPARENT_HUGEPAGE +# Selected by DAX drivers that do not expect filesystem DAX to support +# get_user_pages() of DAX mappings. I.e. "limited" indicates no support +# for fork() of processes with MAP_SHARED mappings or support for +# direct-I/O to a DAX mapping. +config FS_DAX_LIMITED + bool + endif # BLOCK # Posix ACL utility routines |