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Commit 163e11bc authored by Andrea Arcangeli's avatar Andrea Arcangeli Committed by Linus Torvalds
Browse files

userfaultfd: hugetlbfs: UFFD_FEATURE_MISSING_HUGETLBFS 

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: default avatarAndrea 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 21205bf8

include/uapi/linux/userfaultfd.h

+25 −3
Original line number Diff line number Diff line
@@ -20,7 +20,8 @@ 
#define UFFD_API ((__u64)0xAA)

#define UFFD_API_FEATURES (UFFD_FEATURE_EVENT_FORK |		\

			   UFFD_FEATURE_EVENT_REMAP |		\

			   UFFD_FEATURE_EVENT_MADVDONTNEED)

			   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;