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| author | Dan Williams <dan.j.williams@intel.com> | 2017-10-14 21:33:32 +0300 |
|---|---|---|
| committer | Dan Williams <dan.j.williams@intel.com> | 2018-01-20 03:50:53 +0300 |
| commit | 569d0365f571fa6421a5c80bc30d1b2cdab857fe (patch) | |
| tree | 5f8be5e460e8d764a0481dda710e2131cdfb1991 /drivers/s390/block | |
| parent | b4b5798cea8f40ab61f3a2c79a26314465dd83e3 (diff) | |
| download | linux-569d0365f571fa6421a5c80bc30d1b2cdab857fe.tar.xz | |
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 'drivers/s390/block')
| -rw-r--r-- | drivers/s390/block/Kconfig | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/drivers/s390/block/Kconfig b/drivers/s390/block/Kconfig index bc27d716aa6b..1444333210c7 100644 --- a/drivers/s390/block/Kconfig +++ b/drivers/s390/block/Kconfig @@ -16,6 +16,7 @@ config BLK_DEV_XPRAM config DCSSBLK def_tristate m select DAX + select FS_DAX_LIMITED prompt "DCSSBLK support" depends on S390 && BLOCK help |