The patch titled
Subject: userfaultfd/shmem: support minor fault registration for shmem
has been added to the -mm tree. Its filename is
userfaultfd-shmem-support-minor-fault-registration-for-shmem.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/userfaultfd-shmem-support-minor-fault-registration-for-shmem.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/userfaultfd-shmem-support-minor-fault-registration-for-shmem.patch
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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
Subject: userfaultfd/shmem: support minor fault registration for shmem
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.
Link: https://lkml.kernel.org/r/20210503180737.2487560-4-axelrasmussen@xxxxxxxxxx
Signed-off-by: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
Acked-by: Peter Xu <peterx@xxxxxxxxxx>
Acked-by: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Brian Geffon <bgeffon@xxxxxxxxxx>
Cc: "Dr . David Alan Gilbert" <dgilbert@xxxxxxxxxx>
Cc: Jerome Glisse <jglisse@xxxxxxxxxx>
Cc: Joe Perches <joe@xxxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx>
Cc: Lokesh Gidra <lokeshgidra@xxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
Cc: Mina Almasry <almasrymina@xxxxxxxxxx>
Cc: Oliver Upton <oupton@xxxxxxxxxx>
Cc: Shaohua Li <shli@xxxxxx>
Cc: Shuah Khan <shuah@xxxxxxxxxx>
Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
Cc: Wang Qing <wangqing@xxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/userfaultfd.c | 3 +--
mm/memory.c | 8 +++++---
mm/shmem.c | 12 +++++++++++-
3 files changed, 17 insertions(+), 6 deletions(-)
--- a/fs/userfaultfd.c~userfaultfd-shmem-support-minor-fault-registration-for-shmem
+++ a/fs/userfaultfd.c
@@ -1267,8 +1267,7 @@ static inline bool vma_can_userfault(str
}
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;
}
--- a/mm/memory.c~userfaultfd-shmem-support-minor-fault-registration-for-shmem
+++ a/mm/memory.c
@@ -3973,9 +3973,11 @@ static vm_fault_t do_read_fault(struct v
* 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);
--- a/mm/shmem.c~userfaultfd-shmem-support-minor-fault-registration-for-shmem
+++ a/mm/shmem.c
@@ -1785,7 +1785,7 @@ unlock:
* 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 @@ repeat:
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);
_
Patches currently in -mm which might be from axelrasmussen@xxxxxxxxxx are
userfaultfd-release-page-in-error-path-to-avoid-bug_on.patch
userfaultfd-hugetlbfs-avoid-including-userfaultfd_kh-in-hugetlbh.patch
userfaultfd-shmem-combine-shmem_mcopy_atomicmfill_zeropage_pte.patch
userfaultfd-shmem-support-minor-fault-registration-for-shmem.patch
userfaultfd-shmem-support-uffdio_continue-for-shmem.patch
userfaultfd-shmem-advertise-shmem-minor-fault-support.patch
userfaultfd-shmem-modify-shmem_mfill_atomic_pte-to-use-install_pte.patch
userfaultfd-selftests-use-memfd_create-for-shmem-test-type.patch
userfaultfd-selftests-create-alias-mappings-in-the-shmem-test.patch
userfaultfd-selftests-reinitialize-test-context-in-each-test.patch
userfaultfd-selftests-exercise-minor-fault-handling-shmem-support.patch
