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: 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>
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@ -18,9 +18,10 @@
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* means the userland is reading).
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*/
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#define UFFD_API ((__u64)0xAA)
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#define UFFD_API_FEATURES (UFFD_FEATURE_EVENT_FORK | \
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UFFD_FEATURE_EVENT_REMAP | \
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UFFD_FEATURE_EVENT_MADVDONTNEED)
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#define UFFD_API_FEATURES (UFFD_FEATURE_EVENT_FORK | \
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UFFD_FEATURE_EVENT_REMAP | \
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UFFD_FEATURE_EVENT_MADVDONTNEED | \
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UFFD_FEATURE_MISSING_HUGETLBFS)
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#define UFFD_API_IOCTLS \
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((__u64)1 << _UFFDIO_REGISTER | \
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(__u64)1 << _UFFDIO_UNREGISTER | \
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@ -125,11 +126,32 @@ struct uffdio_api {
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* Note: UFFD_EVENT_PAGEFAULT and UFFD_PAGEFAULT_FLAG_WRITE
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* are to be considered implicitly always enabled in all kernels as
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* long as the uffdio_api.api requested matches UFFD_API.
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*
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* UFFD_FEATURE_MISSING_HUGETLBFS means an UFFDIO_REGISTER
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* with UFFDIO_REGISTER_MODE_MISSING mode will succeed on
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* hugetlbfs virtual memory ranges. Adding or not adding
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* UFFD_FEATURE_MISSING_HUGETLBFS to uffdio_api.features has
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* no real functional effect after UFFDIO_API returns, but
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* it's only useful for an initial feature set probe at
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* UFFDIO_API time. There are two ways to use it:
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*
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* 1) by adding UFFD_FEATURE_MISSING_HUGETLBFS to the
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* uffdio_api.features before calling UFFDIO_API, an error
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* will be returned by UFFDIO_API on a kernel without
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* hugetlbfs missing support
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*
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* 2) the UFFD_FEATURE_MISSING_HUGETLBFS can not be added in
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* uffdio_api.features and instead it will be set by the
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* kernel in the uffdio_api.features if the kernel supports
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* it, so userland can later check if the feature flag is
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* present in uffdio_api.features after UFFDIO_API
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* succeeded.
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*/
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#define UFFD_FEATURE_PAGEFAULT_FLAG_WP (1<<0)
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#define UFFD_FEATURE_EVENT_FORK (1<<1)
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#define UFFD_FEATURE_EVENT_REMAP (1<<2)
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#define UFFD_FEATURE_EVENT_MADVDONTNEED (1<<3)
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#define UFFD_FEATURE_MISSING_HUGETLBFS (1<<4)
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__u64 features;
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__u64 ioctls;
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