userfaultfd: wp: add the writeprotect API to userfaultfd ioctl

Introduce the new uffd-wp APIs for userspace.

Firstly, we'll allow to do UFFDIO_REGISTER with write protection tracking
using the new UFFDIO_REGISTER_MODE_WP flag.  Note that this flag can
co-exist with the existing UFFDIO_REGISTER_MODE_MISSING, in which case the
userspace program can not only resolve missing page faults, and at the
same time tracking page data changes along the way.

Secondly, we introduced the new UFFDIO_WRITEPROTECT API to do page level
write protection tracking.  Note that we will need to register the memory
region with UFFDIO_REGISTER_MODE_WP before that.

[peterx@redhat.com: write up the commit message]
[peterx@redhat.com: remove useless block, write commit message, check against
 VM_MAYWRITE rather than VM_WRITE when register]
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Jerome Glisse <jglisse@redhat.com>
Cc: Bobby Powers <bobbypowers@gmail.com>
Cc: Brian Geffon <bgeffon@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Denis Plotnikov <dplotnikov@virtuozzo.com>
Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: "Kirill A . Shutemov" <kirill@shutemov.name>
Cc: Martin Cracauer <cracauer@cons.org>
Cc: Marty McFadden <mcfadden8@llnl.gov>
Cc: Maya Gokhale <gokhale2@llnl.gov>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Shaohua Li <shli@fb.com>
Link: http://lkml.kernel.org/r/20200220163112.11409-14-peterx@redhat.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index c49bef5057750fb835d523fb1f4a2546c20684d3..59e9e399fddbeb60dcd33aaf6c093beef828e2d9 100644 (file)
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -314,8 +314,11 @@ static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx,
        if (!pmd_present(_pmd))
                goto out;
 
-       if (pmd_trans_huge(_pmd))
+       if (pmd_trans_huge(_pmd)) {
+               if (!pmd_write(_pmd) && (reason & VM_UFFD_WP))
+                       ret = true;
                goto out;
+       }
 
        /*
         * the pmd is stable (as in !pmd_trans_unstable) so we can re-read it
@@ -328,6 +331,8 @@ static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx,
         */
        if (pte_none(*pte))
                ret = true;
+       if (!pte_write(*pte) && (reason & VM_UFFD_WP))
+               ret = true;
        pte_unmap(pte);
 
 out:
@@ -1287,10 +1292,13 @@ static __always_inline int validate_range(struct mm_struct *mm,
        return 0;
 }
 
-static inline bool vma_can_userfault(struct vm_area_struct *vma)
+static inline bool vma_can_userfault(struct vm_area_struct *vma,
+                                    unsigned long vm_flags)
 {
-       return vma_is_anonymous(vma) || is_vm_hugetlb_page(vma) ||
-               vma_is_shmem(vma);
+       /* FIXME: add WP support to hugetlbfs and shmem */
+       return vma_is_anonymous(vma) ||
+               ((is_vm_hugetlb_page(vma) || vma_is_shmem(vma)) &&
+                !(vm_flags & VM_UFFD_WP));
 }
 
 static int userfaultfd_register(struct userfaultfd_ctx *ctx,
@@ -1322,15 +1330,8 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
        vm_flags = 0;
        if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING)
                vm_flags |= VM_UFFD_MISSING;
-       if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP) {
+       if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP)
                vm_flags |= VM_UFFD_WP;
-               /*
-                * FIXME: remove the below error constraint by
-                * implementing the wprotect tracking mode.
-                */
-               ret = -EINVAL;
-               goto out;
-       }
 
        ret = validate_range(mm, &uffdio_register.range.start,
                             uffdio_register.range.len);
@@ -1380,7 +1381,7 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
 
                /* check not compatible vmas */
                ret = -EINVAL;
-               if (!vma_can_userfault(cur))
+               if (!vma_can_userfault(cur, vm_flags))
                        goto out_unlock;
 
                /*
@@ -1408,6 +1409,8 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
                        if (end & (vma_hpagesize - 1))
                                goto out_unlock;
                }
+               if ((vm_flags & VM_UFFD_WP) && !(cur->vm_flags & VM_MAYWRITE))
+                       goto out_unlock;
 
                /*
                 * Check that this vma isn't already owned by a
@@ -1437,7 +1440,7 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
        do {
                cond_resched();
 
-               BUG_ON(!vma_can_userfault(vma));
+               BUG_ON(!vma_can_userfault(vma, vm_flags));
                BUG_ON(vma->vm_userfaultfd_ctx.ctx &&
                       vma->vm_userfaultfd_ctx.ctx != ctx);
                WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
@@ -1575,7 +1578,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
                 * provides for more strict behavior to notice
                 * unregistration errors.
                 */
-               if (!vma_can_userfault(cur))
+               if (!vma_can_userfault(cur, cur->vm_flags))
                        goto out_unlock;
 
                found = true;
@@ -1589,7 +1592,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
        do {
                cond_resched();
 
-               BUG_ON(!vma_can_userfault(vma));
+               BUG_ON(!vma_can_userfault(vma, vma->vm_flags));
 
                /*
                 * Nothing to do: this vma is already registered into this
@@ -1802,6 +1805,50 @@ out:
        return ret;
 }
 
+static int userfaultfd_writeprotect(struct userfaultfd_ctx *ctx,
+                                   unsigned long arg)
+{
+       int ret;
+       struct uffdio_writeprotect uffdio_wp;
+       struct uffdio_writeprotect __user *user_uffdio_wp;
+       struct userfaultfd_wake_range range;
+
+       if (READ_ONCE(ctx->mmap_changing))
+               return -EAGAIN;
+
+       user_uffdio_wp = (struct uffdio_writeprotect __user *) arg;
+
+       if (copy_from_user(&uffdio_wp, user_uffdio_wp,
+                          sizeof(struct uffdio_writeprotect)))
+               return -EFAULT;
+
+       ret = validate_range(ctx->mm, &uffdio_wp.range.start,
+                            uffdio_wp.range.len);
+       if (ret)
+               return ret;
+
+       if (uffdio_wp.mode & ~(UFFDIO_WRITEPROTECT_MODE_DONTWAKE |
+                              UFFDIO_WRITEPROTECT_MODE_WP))
+               return -EINVAL;
+       if ((uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_WP) &&
+            (uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_DONTWAKE))
+               return -EINVAL;
+
+       ret = mwriteprotect_range(ctx->mm, uffdio_wp.range.start,
+                                 uffdio_wp.range.len, uffdio_wp.mode &
+                                 UFFDIO_WRITEPROTECT_MODE_WP,
+                                 &ctx->mmap_changing);
+       if (ret)
+               return ret;
+
+       if (!(uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_DONTWAKE)) {
+               range.start = uffdio_wp.range.start;
+               range.len = uffdio_wp.range.len;
+               wake_userfault(ctx, &range);
+       }
+       return ret;
+}
+
 static inline unsigned int uffd_ctx_features(__u64 user_features)
 {
        /*
@@ -1883,6 +1930,9 @@ static long userfaultfd_ioctl(struct file *file, unsigned cmd,
        case UFFDIO_ZEROPAGE:
                ret = userfaultfd_zeropage(ctx, arg);
                break;
+       case UFFDIO_WRITEPROTECT:
+               ret = userfaultfd_writeprotect(ctx, arg);
+               break;
        }
        return ret;
 }

diff --git a/include/uapi/linux/userfaultfd.h b/include/uapi/linux/userfaultfd.h
index 340f23bc251d2053783c2e06d515500d1de592bc..95c4a160e5f8e2c72b0c0faa84f054c30b40def1 100644 (file)
--- a/include/uapi/linux/userfaultfd.h
+++ b/include/uapi/linux/userfaultfd.h
@@ -52,6 +52,7 @@
 #define _UFFDIO_WAKE                   (0x02)
 #define _UFFDIO_COPY                   (0x03)
 #define _UFFDIO_ZEROPAGE               (0x04)
+#define _UFFDIO_WRITEPROTECT           (0x06)
 #define _UFFDIO_API                    (0x3F)
 
 /* userfaultfd ioctl ids */
@@ -68,6 +69,8 @@
                                      struct uffdio_copy)
 #define UFFDIO_ZEROPAGE                _IOWR(UFFDIO, _UFFDIO_ZEROPAGE, \
                                      struct uffdio_zeropage)
+#define UFFDIO_WRITEPROTECT    _IOWR(UFFDIO, _UFFDIO_WRITEPROTECT, \
+                                     struct uffdio_writeprotect)
 
 /* read() structure */
 struct uffd_msg {
@@ -232,4 +235,24 @@ struct uffdio_zeropage {
        __s64 zeropage;
 };
 
+struct uffdio_writeprotect {
+       struct uffdio_range range;
+/*
+ * UFFDIO_WRITEPROTECT_MODE_WP: set the flag to write protect a range,
+ * unset the flag to undo protection of a range which was previously
+ * write protected.
+ *
+ * UFFDIO_WRITEPROTECT_MODE_DONTWAKE: set the flag to avoid waking up
+ * any wait thread after the operation succeeds.
+ *
+ * NOTE: Write protecting a region (WP=1) is unrelated to page faults,
+ * therefore DONTWAKE flag is meaningless with WP=1.  Removing write
+ * protection (WP=0) in response to a page fault wakes the faulting
+ * task unless DONTWAKE is set.
+ */
+#define UFFDIO_WRITEPROTECT_MODE_WP            ((__u64)1<<0)
+#define UFFDIO_WRITEPROTECT_MODE_DONTWAKE      ((__u64)1<<1)
+       __u64 mode;
+};
+
 #endif /* _LINUX_USERFAULTFD_H */