[PATCH v5 03/10] userfaultfd/shmem: support minor fault registration for shmem
From: Axel Rasmussen <axelrasmussen@google.com>
Date: 2021-04-27 22:52:59
Also in:
linux-fsdevel, linux-kselftest, linux-mm, lkml
Subsystem:
filesystems (vfs and infrastructure), memory management, memory management - core, the rest, tmpfs (shmem filesystem) · Maintainers:
Alexander Viro, Christian Brauner, Andrew Morton, David Hildenbrand, Linus Torvalds, Hugh Dickins
This patch allows shmem-backed VMAs to be registered for minor faults. Minor faults are appropriately relayed to userspace in the fault path, for VMAs with the relevant flag. This commit doesn't hook up the UFFDIO_CONTINUE ioctl for shmem-backed minor faults, though, so userspace doesn't yet have a way to resolve such faults. Because of this, we also don't yet advertise this as a supported feature. That will be done in a separate commit when the feature is fully implemented. Acked-by: Peter Xu <peterx@redhat.com> Signed-off-by: Axel Rasmussen <axelrasmussen@google.com> --- fs/userfaultfd.c | 3 +-- mm/memory.c | 8 +++++--- mm/shmem.c | 12 +++++++++++- 3 files changed, 17 insertions(+), 6 deletions(-)
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 14f92285d04f..468556fb04a9 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c@@ -1267,8 +1267,7 @@ static inline bool vma_can_userfault(struct vm_area_struct *vma, } if (vm_flags & VM_UFFD_MINOR) { - /* FIXME: Add minor fault interception for shmem. */ - if (!is_vm_hugetlb_page(vma)) + if (!(is_vm_hugetlb_page(vma) || vma_is_shmem(vma))) return false; }
diff --git a/mm/memory.c b/mm/memory.c
index 4e358601c5d6..cc71a445c76c 100644
--- a/mm/memory.c
+++ b/mm/memory.c@@ -3972,9 +3972,11 @@ static vm_fault_t do_read_fault(struct vm_fault *vmf) * something). */ if (vma->vm_ops->map_pages && fault_around_bytes >> PAGE_SHIFT > 1) { - ret = do_fault_around(vmf); - if (ret) - return ret; + if (likely(!userfaultfd_minor(vmf->vma))) { + ret = do_fault_around(vmf); + if (ret) + return ret; + } } ret = __do_fault(vmf);
diff --git a/mm/shmem.c b/mm/shmem.c
index b72c55aa07fc..30c0bb501dc9 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c@@ -1785,7 +1785,7 @@ static int shmem_swapin_page(struct inode *inode, pgoff_t index, * vm. If we swap it in we mark it dirty since we also free the swap * entry since a page cannot live in both the swap and page cache. * - * vmf and fault_type are only supplied by shmem_fault: + * vma, vmf, and fault_type are only supplied by shmem_fault: * otherwise they are NULL. */ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
@@ -1820,6 +1820,16 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index, page = pagecache_get_page(mapping, index, FGP_ENTRY | FGP_HEAD | FGP_LOCK, 0); + + if (page && vma && userfaultfd_minor(vma)) { + if (!xa_is_value(page)) { + unlock_page(page); + put_page(page); + } + *fault_type = handle_userfault(vmf, VM_UFFD_MINOR); + return 0; + } + if (xa_is_value(page)) { error = shmem_swapin_page(inode, index, &page, sgp, gfp, vma, fault_type);
--
2.31.1.498.g6c1eba8ee3d-goog