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/dev/dax, pmem: direct access to persistent memory Device DAX is the device-centric analogue of Filesystem DAX (CONFIG_FS_DAX). It allows memory ranges to be allocated and mapped without need of an intervening file system. Device DAX is strict, precise and predictable. Specifically this interface: 1/ Guarantees fault granularity with respect to a given page size (pte, pmd, or pud) set at configuration time. 2/ Enforces deterministic behavior by being strict about what fault scenarios are supported. For example, by forcing MADV_DONTFORK semantics and omitting MAP_PRIVATE support device-dax guarantees that a mapping always behaves/performs the same once established. It is the "what you see is what you get" access mechanism to differentiated memory vs filesystem DAX which has filesystem specific implementation semantics. Persistent memory is the first target, but the mechanism is also targeted for exclusive allocations of performance differentiated memory ranges. This commit is limited to the base device driver infrastructure to associate a dax device with pmem range. Cc: Jeff Moyer <jmoyer@redhat.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Ross Zwisler <ross.zwisler@linux.intel.com> Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
2016-05-18 10:15:08 -06:00
menuconfig DEV_DAX
tristate "DAX: direct access to differentiated memory"
default m if NVDIMM_DAX
/dev/dax, core: file operations and dax-mmap The "Device DAX" core enables dax mappings of performance / feature differentiated memory. An open mapping or file handle keeps the backing struct device live, but new mappings are only possible while the device is enabled. Faults are handled under rcu_read_lock to synchronize with the enabled state of the device. Similar to the filesystem-dax case the backing memory may optionally have struct page entries. However, unlike fs-dax there is no support for private mappings, or mappings that are not backed by media (see use of zero-page in fs-dax). Mappings are always guaranteed to match the alignment of the dax_region. If the dax_region is configured to have a 2MB alignment, all mappings are guaranteed to be backed by a pmd entry. Contrast this determinism with the fs-dax case where pmd mappings are opportunistic. If userspace attempts to force a misaligned mapping, the driver will fail the mmap attempt. See dax_dev_check_vma() for other scenarios that are rejected, like MAP_PRIVATE mappings. Cc: Hannes Reinecke <hare@suse.de> Cc: Jeff Moyer <jmoyer@redhat.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Ross Zwisler <ross.zwisler@linux.intel.com> Acked-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
2016-05-14 13:20:44 -06:00
depends on TRANSPARENT_HUGEPAGE
device-dax: switch to srcu, fix rcu_read_lock() vs pte allocation The following warning triggers with a new unit test that stresses the device-dax interface. =============================== [ ERR: suspicious RCU usage. ] 4.11.0-rc4+ #1049 Tainted: G O ------------------------------- ./include/linux/rcupdate.h:521 Illegal context switch in RCU read-side critical section! other info that might help us debug this: rcu_scheduler_active = 2, debug_locks = 0 2 locks held by fio/9070: #0: (&mm->mmap_sem){++++++}, at: [<ffffffff8d0739d7>] __do_page_fault+0x167/0x4f0 #1: (rcu_read_lock){......}, at: [<ffffffffc03fbd02>] dax_dev_huge_fault+0x32/0x620 [dax] Call Trace: dump_stack+0x86/0xc3 lockdep_rcu_suspicious+0xd7/0x110 ___might_sleep+0xac/0x250 __might_sleep+0x4a/0x80 __alloc_pages_nodemask+0x23a/0x360 alloc_pages_current+0xa1/0x1f0 pte_alloc_one+0x17/0x80 __pte_alloc+0x1e/0x120 __get_locked_pte+0x1bf/0x1d0 insert_pfn.isra.70+0x3a/0x100 ? lookup_memtype+0xa6/0xd0 vm_insert_mixed+0x64/0x90 dax_dev_huge_fault+0x520/0x620 [dax] ? dax_dev_huge_fault+0x32/0x620 [dax] dax_dev_fault+0x10/0x20 [dax] __do_fault+0x1e/0x140 __handle_mm_fault+0x9af/0x10d0 handle_mm_fault+0x16d/0x370 ? handle_mm_fault+0x47/0x370 __do_page_fault+0x28c/0x4f0 trace_do_page_fault+0x58/0x2a0 do_async_page_fault+0x1a/0xa0 async_page_fault+0x28/0x30 Inserting a page table entry may trigger an allocation while we are holding a read lock to keep the device instance alive for the duration of the fault. Use srcu for this keep-alive protection. Fixes: dee410792419 ("/dev/dax, core: file operations and dax-mmap") Cc: <stable@vger.kernel.org> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
2017-04-07 17:42:08 -06:00
select SRCU
/dev/dax, pmem: direct access to persistent memory Device DAX is the device-centric analogue of Filesystem DAX (CONFIG_FS_DAX). It allows memory ranges to be allocated and mapped without need of an intervening file system. Device DAX is strict, precise and predictable. Specifically this interface: 1/ Guarantees fault granularity with respect to a given page size (pte, pmd, or pud) set at configuration time. 2/ Enforces deterministic behavior by being strict about what fault scenarios are supported. For example, by forcing MADV_DONTFORK semantics and omitting MAP_PRIVATE support device-dax guarantees that a mapping always behaves/performs the same once established. It is the "what you see is what you get" access mechanism to differentiated memory vs filesystem DAX which has filesystem specific implementation semantics. Persistent memory is the first target, but the mechanism is also targeted for exclusive allocations of performance differentiated memory ranges. This commit is limited to the base device driver infrastructure to associate a dax device with pmem range. Cc: Jeff Moyer <jmoyer@redhat.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Ross Zwisler <ross.zwisler@linux.intel.com> Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
2016-05-18 10:15:08 -06:00
help
Support raw access to differentiated (persistence, bandwidth,
latency...) memory via an mmap(2) capable character
device. Platform firmware or a device driver may identify a
platform memory resource that is differentiated from the
baseline memory pool. Mappings of a /dev/daxX.Y device impose
restrictions that make the mapping behavior deterministic.
if DEV_DAX
config DEV_DAX_PMEM
tristate "PMEM DAX: direct access to persistent memory"
nvdimm: make CONFIG_NVDIMM_DAX 'bool' A bugfix just tried to address a randconfig build problem and introduced a variant of the same problem: with CONFIG_LIBNVDIMM=y and CONFIG_NVDIMM_DAX=m, the nvdimm module now fails to link: drivers/nvdimm/built-in.o: In function `to_nd_device_type': bus.c:(.text+0x1b5d): undefined reference to `is_nd_dax' drivers/nvdimm/built-in.o: In function `nd_region_notify_driver_action.constprop.2': region_devs.c:(.text+0x6b6c): undefined reference to `is_nd_dax' region_devs.c:(.text+0x6b8c): undefined reference to `to_nd_dax' drivers/nvdimm/built-in.o: In function `nd_region_probe': region.c:(.text+0x70f3): undefined reference to `nd_dax_create' drivers/nvdimm/built-in.o: In function `mode_show': namespace_devs.c:(.text+0xa196): undefined reference to `is_nd_dax' drivers/nvdimm/built-in.o: In function `nvdimm_namespace_common_probe': (.text+0xa55f): undefined reference to `is_nd_dax' drivers/nvdimm/built-in.o: In function `nvdimm_namespace_common_probe': (.text+0xa56e): undefined reference to `to_nd_dax' This reverts the earlier fix, making NVDIMM_DAX a 'bool' option again as it should be (it gets linked into the libnvdimm module). To fix the original problem, I'm adding a dependency on LIBNVDIMM to DEV_DAX_PMEM, which ensures we can't have that one built-in if the rest is a module. Fixes: 4e65e9381c7a ("/dev/dax: fix Kconfig dependency build breakage") Signed-off-by: Arnd Bergmann <arnd@arndb.de> Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
2016-10-25 09:52:04 -06:00
depends on LIBNVDIMM && NVDIMM_DAX
/dev/dax, pmem: direct access to persistent memory Device DAX is the device-centric analogue of Filesystem DAX (CONFIG_FS_DAX). It allows memory ranges to be allocated and mapped without need of an intervening file system. Device DAX is strict, precise and predictable. Specifically this interface: 1/ Guarantees fault granularity with respect to a given page size (pte, pmd, or pud) set at configuration time. 2/ Enforces deterministic behavior by being strict about what fault scenarios are supported. For example, by forcing MADV_DONTFORK semantics and omitting MAP_PRIVATE support device-dax guarantees that a mapping always behaves/performs the same once established. It is the "what you see is what you get" access mechanism to differentiated memory vs filesystem DAX which has filesystem specific implementation semantics. Persistent memory is the first target, but the mechanism is also targeted for exclusive allocations of performance differentiated memory ranges. This commit is limited to the base device driver infrastructure to associate a dax device with pmem range. Cc: Jeff Moyer <jmoyer@redhat.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Ross Zwisler <ross.zwisler@linux.intel.com> Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
2016-05-18 10:15:08 -06:00
default DEV_DAX
help
Support raw access to persistent memory. Note that this
driver consumes memory ranges allocated and exported by the
libnvdimm sub-system.
Say Y if unsure
dax: convert to the cdev api A goal of the device-DAX interface is to be able to support many exclusive allocations (partitions) of performance / feature differentiated memory. This count may exceed the default minors limit of 256. As a result of switching to an embedded cdev the inode-to-dax_dev conversion is simplified, as well as reference counting which can switch to the cdev kobject lifetime. Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
2016-07-24 16:55:42 -06:00
config NR_DEV_DAX
int "Maximum number of Device-DAX instances"
default 32768
range 256 2147483647
/dev/dax, pmem: direct access to persistent memory Device DAX is the device-centric analogue of Filesystem DAX (CONFIG_FS_DAX). It allows memory ranges to be allocated and mapped without need of an intervening file system. Device DAX is strict, precise and predictable. Specifically this interface: 1/ Guarantees fault granularity with respect to a given page size (pte, pmd, or pud) set at configuration time. 2/ Enforces deterministic behavior by being strict about what fault scenarios are supported. For example, by forcing MADV_DONTFORK semantics and omitting MAP_PRIVATE support device-dax guarantees that a mapping always behaves/performs the same once established. It is the "what you see is what you get" access mechanism to differentiated memory vs filesystem DAX which has filesystem specific implementation semantics. Persistent memory is the first target, but the mechanism is also targeted for exclusive allocations of performance differentiated memory ranges. This commit is limited to the base device driver infrastructure to associate a dax device with pmem range. Cc: Jeff Moyer <jmoyer@redhat.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Ross Zwisler <ross.zwisler@linux.intel.com> Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
2016-05-18 10:15:08 -06:00
endif