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userfaultfd: hugetlbfs: UFFD_FEATURE_MISSING_HUGETLBFS

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Userland developers asked to be notified immediately by the UFFDIO_API
ioctl if hugetlbfs missing mode is supported by userfaultfd in the
running kernel.  This avoids the need to run UFFDIO_REGISTER on a
hugetlbfs virtual memory range to find out.

Link: http://lkml.kernel.org/r/20161216144821.5183-27-aarcange@redhat.com
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Michael Rapoport <RAPOPORT@il.ibm.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Andrea Arcangeli 2017-02-22 15:43:19 -08:00 committed by Linus Torvalds
parent 21205bf8f7
commit 163e11bc4f
1 changed files with 25 additions and 3 deletions
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28
include/uapi/linux/userfaultfd.h
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@ -18,9 +18,10 @@
* means the userland is reading).
*/
#define UFFD_API ((__u64)0xAA)
#define UFFD_API_FEATURES (UFFD_FEATURE_EVENT_FORK | \
UFFD_FEATURE_EVENT_REMAP | \
UFFD_FEATURE_EVENT_MADVDONTNEED)
#define UFFD_API_FEATURES (UFFD_FEATURE_EVENT_FORK | \
UFFD_FEATURE_EVENT_REMAP | \
UFFD_FEATURE_EVENT_MADVDONTNEED | \
UFFD_FEATURE_MISSING_HUGETLBFS)
#define UFFD_API_IOCTLS \
((__u64)1 << _UFFDIO_REGISTER | \
(__u64)1 << _UFFDIO_UNREGISTER | \
@ -125,11 +126,32 @@ struct uffdio_api {
* Note: UFFD_EVENT_PAGEFAULT and UFFD_PAGEFAULT_FLAG_WRITE
* are to be considered implicitly always enabled in all kernels as
* long as the uffdio_api.api requested matches UFFD_API.
*
* UFFD_FEATURE_MISSING_HUGETLBFS means an UFFDIO_REGISTER
* with UFFDIO_REGISTER_MODE_MISSING mode will succeed on
* hugetlbfs virtual memory ranges. Adding or not adding
* UFFD_FEATURE_MISSING_HUGETLBFS to uffdio_api.features has
* no real functional effect after UFFDIO_API returns, but
* it's only useful for an initial feature set probe at
* UFFDIO_API time. There are two ways to use it:
*
* 1) by adding UFFD_FEATURE_MISSING_HUGETLBFS to the
* uffdio_api.features before calling UFFDIO_API, an error
* will be returned by UFFDIO_API on a kernel without
* hugetlbfs missing support
*
* 2) the UFFD_FEATURE_MISSING_HUGETLBFS can not be added in
* uffdio_api.features and instead it will be set by the
* kernel in the uffdio_api.features if the kernel supports
* it, so userland can later check if the feature flag is
* present in uffdio_api.features after UFFDIO_API
* succeeded.
*/
#define UFFD_FEATURE_PAGEFAULT_FLAG_WP (1<<0)
#define UFFD_FEATURE_EVENT_FORK (1<<1)
#define UFFD_FEATURE_EVENT_REMAP (1<<2)
#define UFFD_FEATURE_EVENT_MADVDONTNEED (1<<3)
#define UFFD_FEATURE_MISSING_HUGETLBFS (1<<4)
__u64 features;
__u64 ioctls;