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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>
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ffd0579396
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63b2d4174c
@ -314,8 +314,11 @@ static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx,
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if (!pmd_present(_pmd))
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goto out;
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if (pmd_trans_huge(_pmd))
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if (pmd_trans_huge(_pmd)) {
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if (!pmd_write(_pmd) && (reason & VM_UFFD_WP))
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ret = true;
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goto out;
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}
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/*
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* the pmd is stable (as in !pmd_trans_unstable) so we can re-read it
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@ -328,6 +331,8 @@ static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx,
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*/
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if (pte_none(*pte))
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ret = true;
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if (!pte_write(*pte) && (reason & VM_UFFD_WP))
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ret = true;
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pte_unmap(pte);
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out:
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@ -1287,10 +1292,13 @@ static __always_inline int validate_range(struct mm_struct *mm,
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return 0;
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}
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static inline bool vma_can_userfault(struct vm_area_struct *vma)
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static inline bool vma_can_userfault(struct vm_area_struct *vma,
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unsigned long vm_flags)
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{
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return vma_is_anonymous(vma) || is_vm_hugetlb_page(vma) ||
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vma_is_shmem(vma);
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/* FIXME: add WP support to hugetlbfs and shmem */
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return vma_is_anonymous(vma) ||
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((is_vm_hugetlb_page(vma) || vma_is_shmem(vma)) &&
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!(vm_flags & VM_UFFD_WP));
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}
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static int userfaultfd_register(struct userfaultfd_ctx *ctx,
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@ -1322,15 +1330,8 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
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vm_flags = 0;
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if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING)
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vm_flags |= VM_UFFD_MISSING;
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if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP) {
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if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP)
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vm_flags |= VM_UFFD_WP;
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/*
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* FIXME: remove the below error constraint by
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* implementing the wprotect tracking mode.
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*/
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ret = -EINVAL;
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goto out;
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}
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ret = validate_range(mm, &uffdio_register.range.start,
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uffdio_register.range.len);
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@ -1380,7 +1381,7 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
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/* check not compatible vmas */
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ret = -EINVAL;
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if (!vma_can_userfault(cur))
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if (!vma_can_userfault(cur, vm_flags))
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goto out_unlock;
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/*
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@ -1408,6 +1409,8 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
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if (end & (vma_hpagesize - 1))
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goto out_unlock;
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}
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if ((vm_flags & VM_UFFD_WP) && !(cur->vm_flags & VM_MAYWRITE))
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goto out_unlock;
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/*
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* Check that this vma isn't already owned by a
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@ -1437,7 +1440,7 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
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do {
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cond_resched();
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BUG_ON(!vma_can_userfault(vma));
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BUG_ON(!vma_can_userfault(vma, vm_flags));
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BUG_ON(vma->vm_userfaultfd_ctx.ctx &&
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vma->vm_userfaultfd_ctx.ctx != ctx);
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WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
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@ -1575,7 +1578,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
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* provides for more strict behavior to notice
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* unregistration errors.
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*/
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if (!vma_can_userfault(cur))
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if (!vma_can_userfault(cur, cur->vm_flags))
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goto out_unlock;
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found = true;
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@ -1589,7 +1592,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
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do {
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cond_resched();
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BUG_ON(!vma_can_userfault(vma));
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BUG_ON(!vma_can_userfault(vma, vma->vm_flags));
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/*
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* Nothing to do: this vma is already registered into this
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@ -1802,6 +1805,50 @@ out:
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return ret;
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}
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static int userfaultfd_writeprotect(struct userfaultfd_ctx *ctx,
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unsigned long arg)
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{
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int ret;
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struct uffdio_writeprotect uffdio_wp;
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struct uffdio_writeprotect __user *user_uffdio_wp;
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struct userfaultfd_wake_range range;
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if (READ_ONCE(ctx->mmap_changing))
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return -EAGAIN;
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user_uffdio_wp = (struct uffdio_writeprotect __user *) arg;
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if (copy_from_user(&uffdio_wp, user_uffdio_wp,
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sizeof(struct uffdio_writeprotect)))
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return -EFAULT;
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ret = validate_range(ctx->mm, &uffdio_wp.range.start,
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uffdio_wp.range.len);
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if (ret)
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return ret;
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if (uffdio_wp.mode & ~(UFFDIO_WRITEPROTECT_MODE_DONTWAKE |
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UFFDIO_WRITEPROTECT_MODE_WP))
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return -EINVAL;
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if ((uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_WP) &&
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(uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_DONTWAKE))
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return -EINVAL;
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ret = mwriteprotect_range(ctx->mm, uffdio_wp.range.start,
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uffdio_wp.range.len, uffdio_wp.mode &
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UFFDIO_WRITEPROTECT_MODE_WP,
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&ctx->mmap_changing);
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if (ret)
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return ret;
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if (!(uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_DONTWAKE)) {
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range.start = uffdio_wp.range.start;
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range.len = uffdio_wp.range.len;
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wake_userfault(ctx, &range);
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}
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return ret;
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}
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static inline unsigned int uffd_ctx_features(__u64 user_features)
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{
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/*
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@ -1883,6 +1930,9 @@ static long userfaultfd_ioctl(struct file *file, unsigned cmd,
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case UFFDIO_ZEROPAGE:
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ret = userfaultfd_zeropage(ctx, arg);
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break;
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case UFFDIO_WRITEPROTECT:
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ret = userfaultfd_writeprotect(ctx, arg);
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break;
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}
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return ret;
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}
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@ -52,6 +52,7 @@
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#define _UFFDIO_WAKE (0x02)
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#define _UFFDIO_COPY (0x03)
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#define _UFFDIO_ZEROPAGE (0x04)
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#define _UFFDIO_WRITEPROTECT (0x06)
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#define _UFFDIO_API (0x3F)
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/* userfaultfd ioctl ids */
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@ -68,6 +69,8 @@
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struct uffdio_copy)
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#define UFFDIO_ZEROPAGE _IOWR(UFFDIO, _UFFDIO_ZEROPAGE, \
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struct uffdio_zeropage)
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#define UFFDIO_WRITEPROTECT _IOWR(UFFDIO, _UFFDIO_WRITEPROTECT, \
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struct uffdio_writeprotect)
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/* read() structure */
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struct uffd_msg {
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@ -232,4 +235,24 @@ struct uffdio_zeropage {
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__s64 zeropage;
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};
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struct uffdio_writeprotect {
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struct uffdio_range range;
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/*
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* UFFDIO_WRITEPROTECT_MODE_WP: set the flag to write protect a range,
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* unset the flag to undo protection of a range which was previously
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* write protected.
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*
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* UFFDIO_WRITEPROTECT_MODE_DONTWAKE: set the flag to avoid waking up
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* any wait thread after the operation succeeds.
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*
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* NOTE: Write protecting a region (WP=1) is unrelated to page faults,
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* therefore DONTWAKE flag is meaningless with WP=1. Removing write
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* protection (WP=0) in response to a page fault wakes the faulting
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* task unless DONTWAKE is set.
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*/
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#define UFFDIO_WRITEPROTECT_MODE_WP ((__u64)1<<0)
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#define UFFDIO_WRITEPROTECT_MODE_DONTWAKE ((__u64)1<<1)
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__u64 mode;
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};
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#endif /* _LINUX_USERFAULTFD_H */
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