[PATCH v5 25/26] mm/userfaultfd: Enable write protection for shmem & hugetlbfs

Peter Xu
2021-07-15T20:18:06Z

We've had all the necessary changes ready for both shmem and hugetlbfs. Turn
on all the shmem/hugetlbfs switches for userfaultfd-wp.

We can expand UFFD_API_RANGE_IOCTLS_BASIC with _UFFDIO_WRITEPROTECT too because
all existing types now support write protection mode.

Since vma_can_userfault() will be used elsewhere, move into userfaultfd_k.h.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
fs/userfaultfd.c | 21 ++-------------------
include/linux/userfaultfd_k.h | 12 ++++++++++++
include/uapi/linux/userfaultfd.h | 10 ++++++++--
mm/userfaultfd.c | 9 +++------
4 files changed, 25 insertions(+), 27 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 644df737fbb2..980879117110 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1275,24 +1275,6 @@ static __always_inline int validate_range(struct mm_struct *mm,
return 0;
}

-static inline bool vma_can_userfault(struct vm_area_struct *vma,
- unsigned long vm_flags)
-{
- /* FIXME: add WP support to hugetlbfs and shmem */
- if (vm_flags & VM_UFFD_WP) {
- if (is_vm_hugetlb_page(vma) || vma_is_shmem(vma))
- return false;
- }
-
- if (vm_flags & VM_UFFD_MINOR) {
- if (!(is_vm_hugetlb_page(vma) || vma_is_shmem(vma)))
- return false;
- }
-
- return vma_is_anonymous(vma) || is_vm_hugetlb_page(vma) ||
- vma_is_shmem(vma);
-}
-
static int userfaultfd_register(struct userfaultfd_ctx *ctx,
unsigned long arg)
{
@@ -1966,7 +1948,8 @@ static int userfaultfd_api(struct userfaultfd_ctx *ctx,
~(UFFD_FEATURE_MINOR_HUGETLBFS | UFFD_FEATURE_MINOR_SHMEM);
#endif
#ifndef CONFIG_HAVE_ARCH_USERFAULTFD_WP
- uffdio_api.features &= ~UFFD_FEATURE_PAGEFAULT_FLAG_WP;
+ uffdio_api.features &=
+ ~(UFFD_FEATURE_PAGEFAULT_FLAG_WP | UFFD_FEATURE_WP_HUGETLBFS_SHMEM);
#endif
uffdio_api.ioctls = UFFD_API_IOCTLS;
ret = -EFAULT;
diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h
index 92606d95b005..4382240de7c3 100644
--- a/include/linux/userfaultfd_k.h
+++ b/include/linux/userfaultfd_k.h
@@ -16,6 +16,7 @@
#include <linux/fcntl.h>
#include <linux/mm.h>
#include <asm-generic/pgtable_uffd.h>
+#include <linux/hugetlb_inline.h>

/* The set of all possible UFFD-related VM flags. */
#define __VM_UFFD_FLAGS (VM_UFFD_MISSING | VM_UFFD_WP | VM_UFFD_MINOR)
@@ -138,6 +139,17 @@ static inline bool userfaultfd_armed(struct vm_area_struct *vma)
return vma->vm_flags & __VM_UFFD_FLAGS;
}

+static inline bool vma_can_userfault(struct vm_area_struct *vma,
+ unsigned long vm_flags)
+{
+ if (vm_flags & VM_UFFD_MINOR)
+ return is_vm_hugetlb_page(vma) || vma_is_shmem(vma);
+
+ return vma_is_anonymous(vma) || is_vm_hugetlb_page(vma) ||
+ vma_is_shmem(vma);
+}
+
+
extern int dup_userfaultfd(struct vm_area_struct *, struct list_head *);
extern void dup_userfaultfd_complete(struct list_head *);

diff --git a/include/uapi/linux/userfaultfd.h b/include/uapi/linux/userfaultfd.h
index 05b31d60acf6..a67b5185a7a9 100644
--- a/include/uapi/linux/userfaultfd.h
+++ b/include/uapi/linux/userfaultfd.h
@@ -32,7 +32,8 @@
UFFD_FEATURE_SIGBUS | \
UFFD_FEATURE_THREAD_ID | \
UFFD_FEATURE_MINOR_HUGETLBFS | \
- UFFD_FEATURE_MINOR_SHMEM)
+ UFFD_FEATURE_MINOR_SHMEM | \
+ UFFD_FEATURE_WP_HUGETLBFS_SHMEM)
#define UFFD_API_IOCTLS \
((__u64)1 << _UFFDIO_REGISTER | \
(__u64)1 << _UFFDIO_UNREGISTER | \
@@ -46,7 +47,8 @@
#define UFFD_API_RANGE_IOCTLS_BASIC \
((__u64)1 << _UFFDIO_WAKE | \
(__u64)1 << _UFFDIO_COPY | \
- (__u64)1 << _UFFDIO_CONTINUE)
+ (__u64)1 << _UFFDIO_CONTINUE | \
+ (__u64)1 << _UFFDIO_WRITEPROTECT)

/*
* Valid ioctl command number range with this API is from 0x00 to
@@ -189,6 +191,9 @@ struct uffdio_api {
*
* UFFD_FEATURE_MINOR_SHMEM indicates the same support as
* UFFD_FEATURE_MINOR_HUGETLBFS, but for shmem-backed pages instead.
+ *
+ * UFFD_FEATURE_WP_HUGETLBFS_SHMEM indicates that userfaultfd
+ * write-protection mode is supported on both shmem and hugetlbfs.
*/
#define UFFD_FEATURE_PAGEFAULT_FLAG_WP (1<<0)
#define UFFD_FEATURE_EVENT_FORK (1<<1)
@@ -201,6 +206,7 @@ struct uffdio_api {
#define UFFD_FEATURE_THREAD_ID (1<<8)
#define UFFD_FEATURE_MINOR_HUGETLBFS (1<<9)
#define UFFD_FEATURE_MINOR_SHMEM (1<<10)
+#define UFFD_FEATURE_WP_HUGETLBFS_SHMEM (1<<11)
__u64 features;

__u64 ioctls;
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index a8038903effd..6587ed787707 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -724,15 +724,12 @@ int mwriteprotect_range(struct mm_struct *dst_mm, unsigned long start,

err = -ENOENT;
dst_vma = find_dst_vma(dst_mm, start, len);
- /*
- * Make sure the vma is not shared, that the dst range is
- * both valid and fully within a single existing vma.
- */
- if (!dst_vma || (dst_vma->vm_flags & VM_SHARED))
+
+ if (!dst_vma)
goto out_unlock;
if (!userfaultfd_wp(dst_vma))
goto out_unlock;
- if (!vma_is_anonymous(dst_vma))
+ if (!vma_can_userfault(dst_vma, dst_vma->vm_flags))
goto out_unlock;

if (is_vm_hugetlb_page(dst_vma)) {
--
2.31.1