diff options
| author | Kiryl Shutsemau (Meta) <kas@kernel.org> | 2026-07-08 12:14:13 +0100 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2026-08-04 19:18:39 -0700 |
| commit | 45347e3d32c15bc70f097bef9ef1a7b90218d450 (patch) | |
| tree | 17d45560378dd54b1a5ed981293d3d4aa77097a2 /include/uapi/linux | |
| parent | 3389648819829299517a8d482fda213fd7166a2c (diff) | |
userfaultfd: add UFFD_FEATURE_RWP_ASYNC for async fault resolution
Sync RWP delivers a message and blocks the faulting thread until the
handler resolves the fault. For working-set tracking the VMM does not
need the message: it just needs to know, at scan time, which pages were
touched. Async RWP serves that use case — the kernel restores access
in-place and the faulting thread continues without blocking.
The VMM reconstructs the access pattern after the fact via PAGEMAP_SCAN:
pages whose uffd bit is still set (inverted PAGE_IS_ACCESSED) were not
re-accessed since the last RWP cycle.
Worth calling out: async resolution upgrades writable private anon PTEs
via pte_mkwrite() when can_change_pte_writable() allows, mirroring
do_numa_page(). Without it, every re-access of an RWP'd writable page
would COW-fault a second time.
UFFD_FEATURE_RWP_ASYNC requires UFFD_FEATURE_RWP.
Link: https://lore.kernel.org/20260708111417.173443-13-kirill@shutemov.name
Signed-off-by: Kiryl Shutsemau <kas@kernel.org>
Assisted-by: Claude:claude-opus-4-6
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: James Houghton <jthoughton@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'include/uapi/linux')
| -rw-r--r-- | include/uapi/linux/userfaultfd.h | 11 |
1 files changed, 10 insertions, 1 deletions
diff --git a/include/uapi/linux/userfaultfd.h b/include/uapi/linux/userfaultfd.h index d803e76d47ad..c10f08f8a618 100644 --- a/include/uapi/linux/userfaultfd.h +++ b/include/uapi/linux/userfaultfd.h @@ -44,7 +44,8 @@ UFFD_FEATURE_POISON | \ UFFD_FEATURE_WP_ASYNC | \ UFFD_FEATURE_MOVE | \ - UFFD_FEATURE_RWP) + UFFD_FEATURE_RWP | \ + UFFD_FEATURE_RWP_ASYNC) #define UFFD_API_IOCTLS \ ((__u64)1 << _UFFDIO_REGISTER | \ (__u64)1 << _UFFDIO_UNREGISTER | \ @@ -243,6 +244,13 @@ struct uffdio_api { * UFFDIO_REGISTER_MODE_RWP for read-write protection tracking. * Pages are made inaccessible via UFFDIO_RWPROTECT and faults * are delivered when the pages are re-accessed. + * + * UFFD_FEATURE_RWP_ASYNC indicates asynchronous mode for + * UFFDIO_REGISTER_MODE_RWP. When set, faults on read-write + * protected pages are auto-resolved by the kernel (PTE + * permissions restored immediately) without delivering a message + * to the userfaultfd handler. Use PAGEMAP_SCAN with inverted + * PAGE_IS_ACCESSED to find pages that were not re-accessed. */ #define UFFD_FEATURE_PAGEFAULT_FLAG_WP (1<<0) #define UFFD_FEATURE_EVENT_FORK (1<<1) @@ -262,6 +270,7 @@ struct uffdio_api { #define UFFD_FEATURE_WP_ASYNC (1<<15) #define UFFD_FEATURE_MOVE (1<<16) #define UFFD_FEATURE_RWP (1<<17) +#define UFFD_FEATURE_RWP_ASYNC (1<<18) __u64 features; __u64 ioctls; |