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.

Andrea Arcangeli committed 9 years ago

Commit 163e11b1 parent 21205bf1 file · +25 −3Browse files

Showing the changes to include/uapi/linux (1 of 1 file). Show all

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include/uapi/linux/userfaultfd.h+25−3

@@ -18,9 +18,10 @@ · 17 unmodified lines
18	18	* means the userland is reading).
19	19	*/
20	20	#define UFFD_API ((__u64)0xAA)
21		−#define UFFD_API_FEATURES (UFFD_FEATURE_EVENT_FORK \| \
22		− UFFD_FEATURE_EVENT_REMAP \| \
23		− UFFD_FEATURE_EVENT_MADVDONTNEED)
	21	+#define UFFD_API_FEATURES (UFFD_FEATURE_EVENT_FORK \| \
	22	+ UFFD_FEATURE_EVENT_REMAP \| \
	23	+ UFFD_FEATURE_EVENT_MADVDONTNEED \| \
	24	+ UFFD_FEATURE_MISSING_HUGETLBFS)
24	25	#define UFFD_API_IOCTLS \
25	26	((__u64)1 << _UFFDIO_REGISTER \| \
26	27	(__u64)1 << _UFFDIO_UNREGISTER \| \
@@ -125,11 +126,32 @@ struct uffdio_api { · 98 unmodified lines
125	126	* Note: UFFD_EVENT_PAGEFAULT and UFFD_PAGEFAULT_FLAG_WRITE
126	127	* are to be considered implicitly always enabled in all kernels as
127	128	* long as the uffdio_api.api requested matches UFFD_API.
	129	+ *
	130	+ * UFFD_FEATURE_MISSING_HUGETLBFS means an UFFDIO_REGISTER
	131	+ * with UFFDIO_REGISTER_MODE_MISSING mode will succeed on
	132	+ * hugetlbfs virtual memory ranges. Adding or not adding
	133	+ * UFFD_FEATURE_MISSING_HUGETLBFS to uffdio_api.features has
	134	+ * no real functional effect after UFFDIO_API returns, but
	135	+ * it's only useful for an initial feature set probe at
	136	+ * UFFDIO_API time. There are two ways to use it:
	137	+ *
	138	+ * 1) by adding UFFD_FEATURE_MISSING_HUGETLBFS to the
	139	+ * uffdio_api.features before calling UFFDIO_API, an error
	140	+ * will be returned by UFFDIO_API on a kernel without
	141	+ * hugetlbfs missing support
	142	+ *
	143	+ * 2) the UFFD_FEATURE_MISSING_HUGETLBFS can not be added in
	144	+ * uffdio_api.features and instead it will be set by the
	145	+ * kernel in the uffdio_api.features if the kernel supports
	146	+ * it, so userland can later check if the feature flag is
	147	+ * present in uffdio_api.features after UFFDIO_API
	148	+ * succeeded.
128	149	*/
129	150	#define UFFD_FEATURE_PAGEFAULT_FLAG_WP (1<<0)
130	151	#define UFFD_FEATURE_EVENT_FORK (1<<1)
131	152	#define UFFD_FEATURE_EVENT_REMAP (1<<2)
132	153	#define UFFD_FEATURE_EVENT_MADVDONTNEED (1<<3)
	154	+#define UFFD_FEATURE_MISSING_HUGETLBFS (1<<4)
133	155	__u64 features;
134	156
135	157	__u64 ioctls;