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The data offset for a dax region needs to account for a reservation in
the resource range. Otherwise, device-dax is allowing mappings directly
into the memmap or device-info-block area with crash signatures like the
following:
BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
IP: get_zone_device_page+0x11/0x30
Call Trace:
follow_devmap_pmd+0x298/0x2c0
follow_page_mask+0x275/0x530
__get_user_pages+0xe3/0x750
__gfn_to_pfn_memslot+0x1b2/0x450 [kvm]
tdp_page_fault+0x130/0x280 [kvm]
kvm_mmu_page_fault+0x5f/0xf0 [kvm]
handle_ept_violation+0x94/0x180 [kvm_intel]
vmx_handle_exit+0x1d3/0x1440 [kvm_intel]
kvm_arch_vcpu_ioctl_run+0x81d/0x16a0 [kvm]
kvm_vcpu_ioctl+0x33c/0x620 [kvm]
do_vfs_ioctl+0xa2/0x5d0
SyS_ioctl+0x79/0x90
entry_SYSCALL_64_fastpath+0x1a/0xa4
Fixes: ab68f2622136 ("/dev/dax, pmem: direct access to persistent memory")
Link: http://lkml.kernel.org/r/147205536732.1606.8994275381938837346.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Reported-by: Abhilash Kumar Mulumudi <m.abhilash-kumar@hpe.com>
Reported-by: Toshi Kani <toshi.kani@hpe.com>
Tested-by: Toshi Kani <toshi.kani@hpe.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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If devm_add_action() fails, we are explicitly calling the cleanup to free
the resources allocated. Use the helper devm_add_action_or_reset()
and return directly in case of error, since the cleanup function
has been already called by the helper if there was any error.
Reported-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Signed-off-by: Vikas C Sajjan <vikas.cha.sajjan@hpe.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
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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>
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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>
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