[PATCH 1/2] userfaultfd: merge fs/userfaultfd.c into mm/userfaultfd.c

[Mike Rapoport <rppt@kernel.org>]

From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>

Historically userfaultfd implementation has been split between
fs/userfaultfd.c and mm/userfaultfd.c.

The mm/ part implemented memory management operations, while the fs/ part
implemented file descriptor handling and called into the mm/ part for the
actual memory management work.

This separation is quite artificial and fs/userfaultfd.c does not seem to
belong to fs/ because it's only a user if vfs APIs and like for other
users, for example, memfd and secretmem, the file descriptor handling could
live in mm/ as well.

"Append" fs/userfaultfd.c to mm/userfaultfd and update fs/Makefile and
MAINTAINERS accordingly.

No intended functional changes.

Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Assisted-by: Copilot:claude-opus-4-6
---
 MAINTAINERS      |    1 -
 fs/Makefile      |    1 -
 fs/userfaultfd.c | 2231 ----------------------------------------------
 mm/userfaultfd.c | 2214 +++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 2214 insertions(+), 2233 deletions(-)
 delete mode 100644 fs/userfaultfd.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 2fb1c75afd16..afd3343a7336 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -17071,7 +17071,6 @@ R:	Peter Xu <peterx@redhat.com>
 L:	linux-mm@kvack.org
 S:	Maintained
 F:	Documentation/admin-guide/mm/userfaultfd.rst
-F:	fs/userfaultfd.c
 F:	include/asm-generic/pgtable_uffd.h
 F:	include/linux/userfaultfd_k.h
 F:	include/uapi/linux/userfaultfd.h
diff --git a/fs/Makefile b/fs/Makefile
index ae1b07f9c6a0..89a8a9d207d1 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -27,7 +27,6 @@ obj-y				+= anon_inodes.o
 obj-$(CONFIG_SIGNALFD)		+= signalfd.o
 obj-$(CONFIG_TIMERFD)		+= timerfd.o
 obj-$(CONFIG_EVENTFD)		+= eventfd.o
-obj-$(CONFIG_USERFAULTFD)	+= userfaultfd.o
 obj-$(CONFIG_AIO)               += aio.o
 obj-$(CONFIG_FS_DAX)		+= dax.o
 obj-$(CONFIG_FS_ENCRYPTION)	+= crypto/
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
deleted file mode 100644
index 4b53dc4a3266..000000000000
--- a/fs/userfaultfd.c
+++ /dev/null
@@ -1,2231 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0-only
-/*
- *  fs/userfaultfd.c
- *
- *  Copyright (C) 2007  Davide Libenzi <davidel@xmailserver.org>
- *  Copyright (C) 2008-2009 Red Hat, Inc.
- *  Copyright (C) 2015  Red Hat, Inc.
- *
- *  Some part derived from fs/eventfd.c (anon inode setup) and
- *  mm/ksm.c (mm hashing).
- */
-
-#include <linux/list.h>
-#include <linux/hashtable.h>
-#include <linux/sched/signal.h>
-#include <linux/sched/mm.h>
-#include <linux/mm.h>
-#include <linux/mm_inline.h>
-#include <linux/mmu_notifier.h>
-#include <linux/poll.h>
-#include <linux/slab.h>
-#include <linux/seq_file.h>
-#include <linux/file.h>
-#include <linux/bug.h>
-#include <linux/anon_inodes.h>
-#include <linux/syscalls.h>
-#include <linux/userfaultfd_k.h>
-#include <linux/mempolicy.h>
-#include <linux/ioctl.h>
-#include <linux/security.h>
-#include <linux/hugetlb.h>
-#include <linux/leafops.h>
-#include <linux/miscdevice.h>
-#include <linux/uio.h>
-
-static int sysctl_unprivileged_userfaultfd __read_mostly;
-
-#ifdef CONFIG_SYSCTL
-static const struct ctl_table vm_userfaultfd_table[] = {
-	{
-		.procname	= "unprivileged_userfaultfd",
-		.data		= &sysctl_unprivileged_userfaultfd,
-		.maxlen		= sizeof(sysctl_unprivileged_userfaultfd),
-		.mode		= 0644,
-		.proc_handler	= proc_dointvec_minmax,
-		.extra1		= SYSCTL_ZERO,
-		.extra2		= SYSCTL_ONE,
-	},
-};
-#endif
-
-static struct kmem_cache *userfaultfd_ctx_cachep __ro_after_init;
-
-struct userfaultfd_fork_ctx {
-	struct userfaultfd_ctx *orig;
-	struct userfaultfd_ctx *new;
-	struct list_head list;
-};
-
-struct userfaultfd_unmap_ctx {
-	struct userfaultfd_ctx *ctx;
-	unsigned long start;
-	unsigned long end;
-	struct list_head list;
-};
-
-struct userfaultfd_wait_queue {
-	struct uffd_msg msg;
-	wait_queue_entry_t wq;
-	struct userfaultfd_ctx *ctx;
-	bool waken;
-};
-
-struct userfaultfd_wake_range {
-	unsigned long start;
-	unsigned long len;
-};
-
-/* internal indication that UFFD_API ioctl was successfully executed */
-#define UFFD_FEATURE_INITIALIZED		(1u << 31)
-
-static bool userfaultfd_is_initialized(struct userfaultfd_ctx *ctx)
-{
-	return ctx->features & UFFD_FEATURE_INITIALIZED;
-}
-
-static bool userfaultfd_wp_async_ctx(struct userfaultfd_ctx *ctx)
-{
-	return ctx && (ctx->features & UFFD_FEATURE_WP_ASYNC);
-}
-
-/*
- * Whether WP_UNPOPULATED is enabled on the uffd context.  It is only
- * meaningful when userfaultfd_wp()==true on the vma and when it's
- * anonymous.
- */
-bool userfaultfd_wp_unpopulated(struct vm_area_struct *vma)
-{
-	struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx;
-
-	if (!ctx)
-		return false;
-
-	return ctx->features & UFFD_FEATURE_WP_UNPOPULATED;
-}
-
-static int userfaultfd_wake_function(wait_queue_entry_t *wq, unsigned mode,
-				     int wake_flags, void *key)
-{
-	struct userfaultfd_wake_range *range = key;
-	int ret;
-	struct userfaultfd_wait_queue *uwq;
-	unsigned long start, len;
-
-	uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
-	ret = 0;
-	/* len == 0 means wake all */
-	start = range->start;
-	len = range->len;
-	if (len && (start > uwq->msg.arg.pagefault.address ||
-		    start + len <= uwq->msg.arg.pagefault.address))
-		goto out;
-	WRITE_ONCE(uwq->waken, true);
-	/*
-	 * The Program-Order guarantees provided by the scheduler
-	 * ensure uwq->waken is visible before the task is woken.
-	 */
-	ret = wake_up_state(wq->private, mode);
-	if (ret) {
-		/*
-		 * Wake only once, autoremove behavior.
-		 *
-		 * After the effect of list_del_init is visible to the other
-		 * CPUs, the waitqueue may disappear from under us, see the
-		 * !list_empty_careful() in handle_userfault().
-		 *
-		 * try_to_wake_up() has an implicit smp_mb(), and the
-		 * wq->private is read before calling the extern function
-		 * "wake_up_state" (which in turns calls try_to_wake_up).
-		 */
-		list_del_init(&wq->entry);
-	}
-out:
-	return ret;
-}
-
-/**
- * userfaultfd_ctx_get - Acquires a reference to the internal userfaultfd
- * context.
- * @ctx: [in] Pointer to the userfaultfd context.
- */
-static void userfaultfd_ctx_get(struct userfaultfd_ctx *ctx)
-{
-	refcount_inc(&ctx->refcount);
-}
-
-/**
- * userfaultfd_ctx_put - Releases a reference to the internal userfaultfd
- * context.
- * @ctx: [in] Pointer to userfaultfd context.
- *
- * The userfaultfd context reference must have been previously acquired either
- * with userfaultfd_ctx_get() or userfaultfd_ctx_fdget().
- */
-static void userfaultfd_ctx_put(struct userfaultfd_ctx *ctx)
-{
-	if (refcount_dec_and_test(&ctx->refcount)) {
-		VM_WARN_ON_ONCE(spin_is_locked(&ctx->fault_pending_wqh.lock));
-		VM_WARN_ON_ONCE(waitqueue_active(&ctx->fault_pending_wqh));
-		VM_WARN_ON_ONCE(spin_is_locked(&ctx->fault_wqh.lock));
-		VM_WARN_ON_ONCE(waitqueue_active(&ctx->fault_wqh));
-		VM_WARN_ON_ONCE(spin_is_locked(&ctx->event_wqh.lock));
-		VM_WARN_ON_ONCE(waitqueue_active(&ctx->event_wqh));
-		VM_WARN_ON_ONCE(spin_is_locked(&ctx->fd_wqh.lock));
-		VM_WARN_ON_ONCE(waitqueue_active(&ctx->fd_wqh));
-		mmdrop(ctx->mm);
-		kmem_cache_free(userfaultfd_ctx_cachep, ctx);
-	}
-}
-
-static inline void msg_init(struct uffd_msg *msg)
-{
-	BUILD_BUG_ON(sizeof(struct uffd_msg) != 32);
-	/*
-	 * Must use memset to zero out the paddings or kernel data is
-	 * leaked to userland.
-	 */
-	memset(msg, 0, sizeof(struct uffd_msg));
-}
-
-static inline struct uffd_msg userfault_msg(unsigned long address,
-					    unsigned long real_address,
-					    unsigned int flags,
-					    unsigned long reason,
-					    unsigned int features)
-{
-	struct uffd_msg msg;
-
-	msg_init(&msg);
-	msg.event = UFFD_EVENT_PAGEFAULT;
-
-	msg.arg.pagefault.address = (features & UFFD_FEATURE_EXACT_ADDRESS) ?
-				    real_address : address;
-
-	/*
-	 * These flags indicate why the userfault occurred:
-	 * - UFFD_PAGEFAULT_FLAG_WP indicates a write protect fault.
-	 * - UFFD_PAGEFAULT_FLAG_MINOR indicates a minor fault.
-	 * - Neither of these flags being set indicates a MISSING fault.
-	 *
-	 * Separately, UFFD_PAGEFAULT_FLAG_WRITE indicates it was a write
-	 * fault. Otherwise, it was a read fault.
-	 */
-	if (flags & FAULT_FLAG_WRITE)
-		msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WRITE;
-	if (reason & VM_UFFD_WP)
-		msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WP;
-	if (reason & VM_UFFD_MINOR)
-		msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_MINOR;
-	if (features & UFFD_FEATURE_THREAD_ID)
-		msg.arg.pagefault.feat.ptid = task_pid_vnr(current);
-	return msg;
-}
-
-#ifdef CONFIG_HUGETLB_PAGE
-/*
- * Same functionality as userfaultfd_must_wait below with modifications for
- * hugepmd ranges.
- */
-static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
-					      struct vm_fault *vmf,
-					      unsigned long reason)
-{
-	struct vm_area_struct *vma = vmf->vma;
-	pte_t *ptep, pte;
-
-	assert_fault_locked(vmf);
-
-	ptep = hugetlb_walk(vma, vmf->address, vma_mmu_pagesize(vma));
-	if (!ptep)
-		return true;
-
-	pte = huge_ptep_get(vma->vm_mm, vmf->address, ptep);
-
-	/*
-	 * Lockless access: we're in a wait_event so it's ok if it
-	 * changes under us.
-	 */
-
-	/* Entry is still missing, wait for userspace to resolve the fault. */
-	if (huge_pte_none(pte))
-		return true;
-	/* UFFD PTE markers require userspace to resolve the fault. */
-	if (pte_is_uffd_marker(pte))
-		return true;
-	/*
-	 * If VMA has UFFD WP faults enabled and WP fault, wait for userspace to
-	 * resolve the fault.
-	 */
-	if (!huge_pte_write(pte) && (reason & VM_UFFD_WP))
-		return true;
-
-	return false;
-}
-#else
-static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
-					      struct vm_fault *vmf,
-					      unsigned long reason)
-{
-	/* Should never get here. */
-	VM_WARN_ON_ONCE(1);
-	return false;
-}
-#endif /* CONFIG_HUGETLB_PAGE */
-
-/*
- * Verify the pagetables are still not ok after having registered into
- * the fault_pending_wqh to avoid userland having to UFFDIO_WAKE any
- * userfault that has already been resolved, if userfaultfd_read_iter and
- * UFFDIO_COPY|ZEROPAGE are being run simultaneously on two different
- * threads.
- */
-static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx,
-					 struct vm_fault *vmf,
-					 unsigned long reason)
-{
-	struct mm_struct *mm = ctx->mm;
-	unsigned long address = vmf->address;
-	pgd_t *pgd;
-	p4d_t *p4d;
-	pud_t *pud;
-	pmd_t *pmd, _pmd;
-	pte_t *pte;
-	pte_t ptent;
-	bool ret;
-
-	assert_fault_locked(vmf);
-
-	pgd = pgd_offset(mm, address);
-	if (!pgd_present(*pgd))
-		return true;
-	p4d = p4d_offset(pgd, address);
-	if (!p4d_present(*p4d))
-		return true;
-	pud = pud_offset(p4d, address);
-	if (!pud_present(*pud))
-		return true;
-	pmd = pmd_offset(pud, address);
-again:
-	_pmd = pmdp_get_lockless(pmd);
-	if (pmd_none(_pmd))
-		return true;
-
-	/*
-	 * A race could arise which would result in a softleaf entry such as
-	 * migration entry unexpectedly being present in the PMD, so explicitly
-	 * check for this and bail out if so.
-	 */
-	if (!pmd_present(_pmd))
-		return false;
-
-	if (pmd_trans_huge(_pmd))
-		return !pmd_write(_pmd) && (reason & VM_UFFD_WP);
-
-	pte = pte_offset_map(pmd, address);
-	if (!pte)
-		goto again;
-
-	/*
-	 * Lockless access: we're in a wait_event so it's ok if it
-	 * changes under us.
-	 */
-	ptent = ptep_get(pte);
-
-	ret = true;
-	/* Entry is still missing, wait for userspace to resolve the fault. */
-	if (pte_none(ptent))
-		goto out;
-	/* UFFD PTE markers require userspace to resolve the fault. */
-	if (pte_is_uffd_marker(ptent))
-		goto out;
-	/*
-	 * If VMA has UFFD WP faults enabled and WP fault, wait for userspace to
-	 * resolve the fault.
-	 */
-	if (!pte_write(ptent) && (reason & VM_UFFD_WP))
-		goto out;
-
-	ret = false;
-out:
-	pte_unmap(pte);
-	return ret;
-}
-
-static inline unsigned int userfaultfd_get_blocking_state(unsigned int flags)
-{
-	if (flags & FAULT_FLAG_INTERRUPTIBLE)
-		return TASK_INTERRUPTIBLE;
-
-	if (flags & FAULT_FLAG_KILLABLE)
-		return TASK_KILLABLE;
-
-	return TASK_UNINTERRUPTIBLE;
-}
-
-/*
- * The locking rules involved in returning VM_FAULT_RETRY depending on
- * FAULT_FLAG_ALLOW_RETRY, FAULT_FLAG_RETRY_NOWAIT and
- * FAULT_FLAG_KILLABLE are not straightforward. The "Caution"
- * recommendation in __lock_page_or_retry is not an understatement.
- *
- * If FAULT_FLAG_ALLOW_RETRY is set, the mmap_lock must be released
- * before returning VM_FAULT_RETRY only if FAULT_FLAG_RETRY_NOWAIT is
- * not set.
- *
- * If FAULT_FLAG_ALLOW_RETRY is set but FAULT_FLAG_KILLABLE is not
- * set, VM_FAULT_RETRY can still be returned if and only if there are
- * fatal_signal_pending()s, and the mmap_lock must be released before
- * returning it.
- */
-vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
-{
-	struct vm_area_struct *vma = vmf->vma;
-	struct mm_struct *mm = vma->vm_mm;
-	struct userfaultfd_ctx *ctx;
-	struct userfaultfd_wait_queue uwq;
-	vm_fault_t ret = VM_FAULT_SIGBUS;
-	bool must_wait;
-	unsigned int blocking_state;
-
-	/*
-	 * We don't do userfault handling for the final child pid update
-	 * and when coredumping (faults triggered by get_dump_page()).
-	 */
-	if (current->flags & (PF_EXITING|PF_DUMPCORE))
-		goto out;
-
-	assert_fault_locked(vmf);
-
-	ctx = vma->vm_userfaultfd_ctx.ctx;
-	if (!ctx)
-		goto out;
-
-	VM_WARN_ON_ONCE(ctx->mm != mm);
-
-	/* Any unrecognized flag is a bug. */
-	VM_WARN_ON_ONCE(reason & ~__VM_UFFD_FLAGS);
-	/* 0 or > 1 flags set is a bug; we expect exactly 1. */
-	VM_WARN_ON_ONCE(!reason || (reason & (reason - 1)));
-
-	if (ctx->features & UFFD_FEATURE_SIGBUS)
-		goto out;
-	if (!(vmf->flags & FAULT_FLAG_USER) && (ctx->flags & UFFD_USER_MODE_ONLY))
-		goto out;
-
-	/*
-	 * Check that we can return VM_FAULT_RETRY.
-	 *
-	 * NOTE: it should become possible to return VM_FAULT_RETRY
-	 * even if FAULT_FLAG_TRIED is set without leading to gup()
-	 * -EBUSY failures, if the userfaultfd is to be extended for
-	 * VM_UFFD_WP tracking and we intend to arm the userfault
-	 * without first stopping userland access to the memory. For
-	 * VM_UFFD_MISSING userfaults this is enough for now.
-	 */
-	if (unlikely(!(vmf->flags & FAULT_FLAG_ALLOW_RETRY))) {
-		/*
-		 * Validate the invariant that nowait must allow retry
-		 * to be sure not to return SIGBUS erroneously on
-		 * nowait invocations.
-		 */
-		VM_WARN_ON_ONCE(vmf->flags & FAULT_FLAG_RETRY_NOWAIT);
-#ifdef CONFIG_DEBUG_VM
-		if (printk_ratelimit()) {
-			pr_warn("FAULT_FLAG_ALLOW_RETRY missing %x\n",
-				vmf->flags);
-			dump_stack();
-		}
-#endif
-		goto out;
-	}
-
-	/*
-	 * Handle nowait, not much to do other than tell it to retry
-	 * and wait.
-	 */
-	ret = VM_FAULT_RETRY;
-	if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
-		goto out;
-
-	if (unlikely(READ_ONCE(ctx->released))) {
-		/*
-		 * If a concurrent release is detected, do not return
-		 * VM_FAULT_SIGBUS or VM_FAULT_NOPAGE, but instead always
-		 * return VM_FAULT_RETRY with lock released proactively.
-		 *
-		 * If we were to return VM_FAULT_SIGBUS here, the non
-		 * cooperative manager would be instead forced to
-		 * always call UFFDIO_UNREGISTER before it can safely
-		 * close the uffd, to avoid involuntary SIGBUS triggered.
-		 *
-		 * If we were to return VM_FAULT_NOPAGE, it would work for
-		 * the fault path, in which the lock will be released
-		 * later.  However for GUP, faultin_page() does nothing
-		 * special on NOPAGE, so GUP would spin retrying without
-		 * releasing the mmap read lock, causing possible livelock.
-		 *
-		 * Here only VM_FAULT_RETRY would make sure the mmap lock
-		 * be released immediately, so that the thread concurrently
-		 * releasing the userfault would always make progress.
-		 */
-		release_fault_lock(vmf);
-		goto out;
-	}
-
-	/* take the reference before dropping the mmap_lock */
-	userfaultfd_ctx_get(ctx);
-
-	init_waitqueue_func_entry(&uwq.wq, userfaultfd_wake_function);
-	uwq.wq.private = current;
-	uwq.msg = userfault_msg(vmf->address, vmf->real_address, vmf->flags,
-				reason, ctx->features);
-	uwq.ctx = ctx;
-	uwq.waken = false;
-
-	blocking_state = userfaultfd_get_blocking_state(vmf->flags);
-
-        /*
-         * Take the vma lock now, in order to safely call
-         * userfaultfd_huge_must_wait() later. Since acquiring the
-         * (sleepable) vma lock can modify the current task state, that
-         * must be before explicitly calling set_current_state().
-         */
-	if (is_vm_hugetlb_page(vma))
-		hugetlb_vma_lock_read(vma);
-
-	spin_lock_irq(&ctx->fault_pending_wqh.lock);
-	/*
-	 * After the __add_wait_queue the uwq is visible to userland
-	 * through poll/read().
-	 */
-	__add_wait_queue(&ctx->fault_pending_wqh, &uwq.wq);
-	/*
-	 * The smp_mb() after __set_current_state prevents the reads
-	 * following the spin_unlock to happen before the list_add in
-	 * __add_wait_queue.
-	 */
-	set_current_state(blocking_state);
-	spin_unlock_irq(&ctx->fault_pending_wqh.lock);
-
-	if (is_vm_hugetlb_page(vma)) {
-		must_wait = userfaultfd_huge_must_wait(ctx, vmf, reason);
-		hugetlb_vma_unlock_read(vma);
-	} else {
-		must_wait = userfaultfd_must_wait(ctx, vmf, reason);
-	}
-
-	release_fault_lock(vmf);
-
-	if (likely(must_wait && !READ_ONCE(ctx->released))) {
-		wake_up_poll(&ctx->fd_wqh, EPOLLIN);
-		schedule();
-	}
-
-	__set_current_state(TASK_RUNNING);
-
-	/*
-	 * Here we race with the list_del; list_add in
-	 * userfaultfd_ctx_read(), however because we don't ever run
-	 * list_del_init() to refile across the two lists, the prev
-	 * and next pointers will never point to self. list_add also
-	 * would never let any of the two pointers to point to
-	 * self. So list_empty_careful won't risk to see both pointers
-	 * pointing to self at any time during the list refile. The
-	 * only case where list_del_init() is called is the full
-	 * removal in the wake function and there we don't re-list_add
-	 * and it's fine not to block on the spinlock. The uwq on this
-	 * kernel stack can be released after the list_del_init.
-	 */
-	if (!list_empty_careful(&uwq.wq.entry)) {
-		spin_lock_irq(&ctx->fault_pending_wqh.lock);
-		/*
-		 * No need of list_del_init(), the uwq on the stack
-		 * will be freed shortly anyway.
-		 */
-		list_del(&uwq.wq.entry);
-		spin_unlock_irq(&ctx->fault_pending_wqh.lock);
-	}
-
-	/*
-	 * ctx may go away after this if the userfault pseudo fd is
-	 * already released.
-	 */
-	userfaultfd_ctx_put(ctx);
-
-out:
-	return ret;
-}
-
-static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
-					      struct userfaultfd_wait_queue *ewq)
-{
-	struct userfaultfd_ctx *release_new_ctx;
-
-	if (WARN_ON_ONCE(current->flags & PF_EXITING))
-		goto out;
-
-	ewq->ctx = ctx;
-	init_waitqueue_entry(&ewq->wq, current);
-	release_new_ctx = NULL;
-
-	spin_lock_irq(&ctx->event_wqh.lock);
-	/*
-	 * After the __add_wait_queue the uwq is visible to userland
-	 * through poll/read().
-	 */
-	__add_wait_queue(&ctx->event_wqh, &ewq->wq);
-	for (;;) {
-		set_current_state(TASK_KILLABLE);
-		if (ewq->msg.event == 0)
-			break;
-		if (READ_ONCE(ctx->released) ||
-		    fatal_signal_pending(current)) {
-			/*
-			 * &ewq->wq may be queued in fork_event, but
-			 * __remove_wait_queue ignores the head
-			 * parameter. It would be a problem if it
-			 * didn't.
-			 */
-			__remove_wait_queue(&ctx->event_wqh, &ewq->wq);
-			if (ewq->msg.event == UFFD_EVENT_FORK) {
-				struct userfaultfd_ctx *new;
-
-				new = (struct userfaultfd_ctx *)
-					(unsigned long)
-					ewq->msg.arg.reserved.reserved1;
-				release_new_ctx = new;
-			}
-			break;
-		}
-
-		spin_unlock_irq(&ctx->event_wqh.lock);
-
-		wake_up_poll(&ctx->fd_wqh, EPOLLIN);
-		schedule();
-
-		spin_lock_irq(&ctx->event_wqh.lock);
-	}
-	__set_current_state(TASK_RUNNING);
-	spin_unlock_irq(&ctx->event_wqh.lock);
-
-	if (release_new_ctx) {
-		userfaultfd_release_new(release_new_ctx);
-		userfaultfd_ctx_put(release_new_ctx);
-	}
-
-	/*
-	 * ctx may go away after this if the userfault pseudo fd is
-	 * already released.
-	 */
-out:
-	atomic_dec(&ctx->mmap_changing);
-	VM_WARN_ON_ONCE(atomic_read(&ctx->mmap_changing) < 0);
-	userfaultfd_ctx_put(ctx);
-}
-
-static void userfaultfd_event_complete(struct userfaultfd_ctx *ctx,
-				       struct userfaultfd_wait_queue *ewq)
-{
-	ewq->msg.event = 0;
-	wake_up_locked(&ctx->event_wqh);
-	__remove_wait_queue(&ctx->event_wqh, &ewq->wq);
-}
-
-int dup_userfaultfd(struct vm_area_struct *vma, struct list_head *fcs)
-{
-	struct userfaultfd_ctx *ctx = NULL, *octx;
-	struct userfaultfd_fork_ctx *fctx;
-
-	octx = vma->vm_userfaultfd_ctx.ctx;
-	if (!octx)
-		return 0;
-
-	if (!(octx->features & UFFD_FEATURE_EVENT_FORK)) {
-		userfaultfd_reset_ctx(vma);
-		return 0;
-	}
-
-	list_for_each_entry(fctx, fcs, list)
-		if (fctx->orig == octx) {
-			ctx = fctx->new;
-			break;
-		}
-
-	if (!ctx) {
-		fctx = kmalloc_obj(*fctx);
-		if (!fctx)
-			return -ENOMEM;
-
-		ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
-		if (!ctx) {
-			kfree(fctx);
-			return -ENOMEM;
-		}
-
-		refcount_set(&ctx->refcount, 1);
-		ctx->flags = octx->flags;
-		ctx->features = octx->features;
-		ctx->released = false;
-		init_rwsem(&ctx->map_changing_lock);
-		atomic_set(&ctx->mmap_changing, 0);
-		ctx->mm = vma->vm_mm;
-		mmgrab(ctx->mm);
-
-		userfaultfd_ctx_get(octx);
-		down_write(&octx->map_changing_lock);
-		atomic_inc(&octx->mmap_changing);
-		up_write(&octx->map_changing_lock);
-		fctx->orig = octx;
-		fctx->new = ctx;
-		list_add_tail(&fctx->list, fcs);
-	}
-
-	vma->vm_userfaultfd_ctx.ctx = ctx;
-	return 0;
-}
-
-static void dup_fctx(struct userfaultfd_fork_ctx *fctx)
-{
-	struct userfaultfd_ctx *ctx = fctx->orig;
-	struct userfaultfd_wait_queue ewq;
-
-	msg_init(&ewq.msg);
-
-	ewq.msg.event = UFFD_EVENT_FORK;
-	ewq.msg.arg.reserved.reserved1 = (unsigned long)fctx->new;
-
-	userfaultfd_event_wait_completion(ctx, &ewq);
-}
-
-void dup_userfaultfd_complete(struct list_head *fcs)
-{
-	struct userfaultfd_fork_ctx *fctx, *n;
-
-	list_for_each_entry_safe(fctx, n, fcs, list) {
-		dup_fctx(fctx);
-		list_del(&fctx->list);
-		kfree(fctx);
-	}
-}
-
-void dup_userfaultfd_fail(struct list_head *fcs)
-{
-	struct userfaultfd_fork_ctx *fctx, *n;
-
-	/*
-	 * An error has occurred on fork, we will tear memory down, but have
-	 * allocated memory for fctx's and raised reference counts for both the
-	 * original and child contexts (and on the mm for each as a result).
-	 *
-	 * These would ordinarily be taken care of by a user handling the event,
-	 * but we are no longer doing so, so manually clean up here.
-	 *
-	 * mm tear down will take care of cleaning up VMA contexts.
-	 */
-	list_for_each_entry_safe(fctx, n, fcs, list) {
-		struct userfaultfd_ctx *octx = fctx->orig;
-		struct userfaultfd_ctx *ctx = fctx->new;
-
-		atomic_dec(&octx->mmap_changing);
-		VM_WARN_ON_ONCE(atomic_read(&octx->mmap_changing) < 0);
-		userfaultfd_ctx_put(octx);
-		userfaultfd_ctx_put(ctx);
-
-		list_del(&fctx->list);
-		kfree(fctx);
-	}
-}
-
-void mremap_userfaultfd_prep(struct vm_area_struct *vma,
-			     struct vm_userfaultfd_ctx *vm_ctx)
-{
-	struct userfaultfd_ctx *ctx;
-
-	ctx = vma->vm_userfaultfd_ctx.ctx;
-
-	if (!ctx)
-		return;
-
-	if (ctx->features & UFFD_FEATURE_EVENT_REMAP) {
-		vm_ctx->ctx = ctx;
-		userfaultfd_ctx_get(ctx);
-		down_write(&ctx->map_changing_lock);
-		atomic_inc(&ctx->mmap_changing);
-		up_write(&ctx->map_changing_lock);
-	} else {
-		/* Drop uffd context if remap feature not enabled */
-		userfaultfd_reset_ctx(vma);
-	}
-}
-
-void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx *vm_ctx,
-				 unsigned long from, unsigned long to,
-				 unsigned long len)
-{
-	struct userfaultfd_ctx *ctx = vm_ctx->ctx;
-	struct userfaultfd_wait_queue ewq;
-
-	if (!ctx)
-		return;
-
-	msg_init(&ewq.msg);
-
-	ewq.msg.event = UFFD_EVENT_REMAP;
-	ewq.msg.arg.remap.from = from;
-	ewq.msg.arg.remap.to = to;
-	ewq.msg.arg.remap.len = len;
-
-	userfaultfd_event_wait_completion(ctx, &ewq);
-}
-
-void mremap_userfaultfd_fail(struct vm_userfaultfd_ctx *vm_ctx)
-{
-	struct userfaultfd_ctx *ctx = vm_ctx->ctx;
-
-	if (!ctx)
-		return;
-
-	userfaultfd_ctx_put(ctx);
-}
-
-bool userfaultfd_remove(struct vm_area_struct *vma,
-			unsigned long start, unsigned long end)
-{
-	struct mm_struct *mm = vma->vm_mm;
-	struct userfaultfd_ctx *ctx;
-	struct userfaultfd_wait_queue ewq;
-
-	ctx = vma->vm_userfaultfd_ctx.ctx;
-	if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_REMOVE))
-		return true;
-
-	userfaultfd_ctx_get(ctx);
-	down_write(&ctx->map_changing_lock);
-	atomic_inc(&ctx->mmap_changing);
-	up_write(&ctx->map_changing_lock);
-	mmap_read_unlock(mm);
-
-	msg_init(&ewq.msg);
-
-	ewq.msg.event = UFFD_EVENT_REMOVE;
-	ewq.msg.arg.remove.start = start;
-	ewq.msg.arg.remove.end = end;
-
-	userfaultfd_event_wait_completion(ctx, &ewq);
-
-	return false;
-}
-
-static bool has_unmap_ctx(struct userfaultfd_ctx *ctx, struct list_head *unmaps,
-			  unsigned long start, unsigned long end)
-{
-	struct userfaultfd_unmap_ctx *unmap_ctx;
-
-	list_for_each_entry(unmap_ctx, unmaps, list)
-		if (unmap_ctx->ctx == ctx && unmap_ctx->start == start &&
-		    unmap_ctx->end == end)
-			return true;
-
-	return false;
-}
-
-int userfaultfd_unmap_prep(struct vm_area_struct *vma, unsigned long start,
-			   unsigned long end, struct list_head *unmaps)
-{
-	struct userfaultfd_unmap_ctx *unmap_ctx;
-	struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx;
-
-	if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_UNMAP) ||
-	    has_unmap_ctx(ctx, unmaps, start, end))
-		return 0;
-
-	unmap_ctx = kzalloc_obj(*unmap_ctx);
-	if (!unmap_ctx)
-		return -ENOMEM;
-
-	userfaultfd_ctx_get(ctx);
-	down_write(&ctx->map_changing_lock);
-	atomic_inc(&ctx->mmap_changing);
-	up_write(&ctx->map_changing_lock);
-	unmap_ctx->ctx = ctx;
-	unmap_ctx->start = start;
-	unmap_ctx->end = end;
-	list_add_tail(&unmap_ctx->list, unmaps);
-
-	return 0;
-}
-
-void userfaultfd_unmap_complete(struct mm_struct *mm, struct list_head *uf)
-{
-	struct userfaultfd_unmap_ctx *ctx, *n;
-	struct userfaultfd_wait_queue ewq;
-
-	list_for_each_entry_safe(ctx, n, uf, list) {
-		msg_init(&ewq.msg);
-
-		ewq.msg.event = UFFD_EVENT_UNMAP;
-		ewq.msg.arg.remove.start = ctx->start;
-		ewq.msg.arg.remove.end = ctx->end;
-
-		userfaultfd_event_wait_completion(ctx->ctx, &ewq);
-
-		list_del(&ctx->list);
-		kfree(ctx);
-	}
-}
-
-static int userfaultfd_release(struct inode *inode, struct file *file)
-{
-	struct userfaultfd_ctx *ctx = file->private_data;
-	struct mm_struct *mm = ctx->mm;
-	/* len == 0 means wake all */
-	struct userfaultfd_wake_range range = { .len = 0, };
-
-	WRITE_ONCE(ctx->released, true);
-
-	userfaultfd_release_all(mm, ctx);
-
-	/*
-	 * After no new page faults can wait on this fault_*wqh, flush
-	 * the last page faults that may have been already waiting on
-	 * the fault_*wqh.
-	 */
-	spin_lock_irq(&ctx->fault_pending_wqh.lock);
-	__wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, &range);
-	__wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, &range);
-	spin_unlock_irq(&ctx->fault_pending_wqh.lock);
-
-	/* Flush pending events that may still wait on event_wqh */
-	wake_up_all(&ctx->event_wqh);
-
-	wake_up_poll(&ctx->fd_wqh, EPOLLHUP);
-	userfaultfd_ctx_put(ctx);
-	return 0;
-}
-
-/* fault_pending_wqh.lock must be hold by the caller */
-static inline struct userfaultfd_wait_queue *find_userfault_in(
-		wait_queue_head_t *wqh)
-{
-	wait_queue_entry_t *wq;
-	struct userfaultfd_wait_queue *uwq;
-
-	lockdep_assert_held(&wqh->lock);
-
-	uwq = NULL;
-	if (!waitqueue_active(wqh))
-		goto out;
-	/* walk in reverse to provide FIFO behavior to read userfaults */
-	wq = list_last_entry(&wqh->head, typeof(*wq), entry);
-	uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
-out:
-	return uwq;
-}
-
-static inline struct userfaultfd_wait_queue *find_userfault(
-		struct userfaultfd_ctx *ctx)
-{
-	return find_userfault_in(&ctx->fault_pending_wqh);
-}
-
-static inline struct userfaultfd_wait_queue *find_userfault_evt(
-		struct userfaultfd_ctx *ctx)
-{
-	return find_userfault_in(&ctx->event_wqh);
-}
-
-static __poll_t userfaultfd_poll(struct file *file, poll_table *wait)
-{
-	struct userfaultfd_ctx *ctx = file->private_data;
-	__poll_t ret;
-
-	poll_wait(file, &ctx->fd_wqh, wait);
-
-	if (!userfaultfd_is_initialized(ctx))
-		return EPOLLERR;
-
-	/*
-	 * poll() never guarantees that read won't block.
-	 * userfaults can be waken before they're read().
-	 */
-	if (unlikely(!(file->f_flags & O_NONBLOCK)))
-		return EPOLLERR;
-	/*
-	 * lockless access to see if there are pending faults
-	 * __pollwait last action is the add_wait_queue but
-	 * the spin_unlock would allow the waitqueue_active to
-	 * pass above the actual list_add inside
-	 * add_wait_queue critical section. So use a full
-	 * memory barrier to serialize the list_add write of
-	 * add_wait_queue() with the waitqueue_active read
-	 * below.
-	 */
-	ret = 0;
-	smp_mb();
-	if (waitqueue_active(&ctx->fault_pending_wqh))
-		ret = EPOLLIN;
-	else if (waitqueue_active(&ctx->event_wqh))
-		ret = EPOLLIN;
-
-	return ret;
-}
-
-static const struct file_operations userfaultfd_fops;
-
-static int resolve_userfault_fork(struct userfaultfd_ctx *new,
-				  struct inode *inode,
-				  struct uffd_msg *msg)
-{
-	int fd;
-
-	fd = anon_inode_create_getfd("[userfaultfd]", &userfaultfd_fops, new,
-			O_RDONLY | (new->flags & UFFD_SHARED_FCNTL_FLAGS), inode);
-	if (fd < 0)
-		return fd;
-
-	msg->arg.reserved.reserved1 = 0;
-	msg->arg.fork.ufd = fd;
-	return 0;
-}
-
-static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
-				    struct uffd_msg *msg, struct inode *inode)
-{
-	ssize_t ret;
-	DECLARE_WAITQUEUE(wait, current);
-	struct userfaultfd_wait_queue *uwq;
-	/*
-	 * Handling fork event requires sleeping operations, so
-	 * we drop the event_wqh lock, then do these ops, then
-	 * lock it back and wake up the waiter. While the lock is
-	 * dropped the ewq may go away so we keep track of it
-	 * carefully.
-	 */
-	LIST_HEAD(fork_event);
-	struct userfaultfd_ctx *fork_nctx = NULL;
-
-	/* always take the fd_wqh lock before the fault_pending_wqh lock */
-	spin_lock_irq(&ctx->fd_wqh.lock);
-	__add_wait_queue(&ctx->fd_wqh, &wait);
-	for (;;) {
-		set_current_state(TASK_INTERRUPTIBLE);
-		spin_lock(&ctx->fault_pending_wqh.lock);
-		uwq = find_userfault(ctx);
-		if (uwq) {
-			/*
-			 * Use a seqcount to repeat the lockless check
-			 * in wake_userfault() to avoid missing
-			 * wakeups because during the refile both
-			 * waitqueue could become empty if this is the
-			 * only userfault.
-			 */
-			write_seqcount_begin(&ctx->refile_seq);
-
-			/*
-			 * The fault_pending_wqh.lock prevents the uwq
-			 * to disappear from under us.
-			 *
-			 * Refile this userfault from
-			 * fault_pending_wqh to fault_wqh, it's not
-			 * pending anymore after we read it.
-			 *
-			 * Use list_del() by hand (as
-			 * userfaultfd_wake_function also uses
-			 * list_del_init() by hand) to be sure nobody
-			 * changes __remove_wait_queue() to use
-			 * list_del_init() in turn breaking the
-			 * !list_empty_careful() check in
-			 * handle_userfault(). The uwq->wq.head list
-			 * must never be empty at any time during the
-			 * refile, or the waitqueue could disappear
-			 * from under us. The "wait_queue_head_t"
-			 * parameter of __remove_wait_queue() is unused
-			 * anyway.
-			 */
-			list_del(&uwq->wq.entry);
-			add_wait_queue(&ctx->fault_wqh, &uwq->wq);
-
-			write_seqcount_end(&ctx->refile_seq);
-
-			/* careful to always initialize msg if ret == 0 */
-			*msg = uwq->msg;
-			spin_unlock(&ctx->fault_pending_wqh.lock);
-			ret = 0;
-			break;
-		}
-		spin_unlock(&ctx->fault_pending_wqh.lock);
-
-		spin_lock(&ctx->event_wqh.lock);
-		uwq = find_userfault_evt(ctx);
-		if (uwq) {
-			*msg = uwq->msg;
-
-			if (uwq->msg.event == UFFD_EVENT_FORK) {
-				fork_nctx = (struct userfaultfd_ctx *)
-					(unsigned long)
-					uwq->msg.arg.reserved.reserved1;
-				list_move(&uwq->wq.entry, &fork_event);
-				/*
-				 * fork_nctx can be freed as soon as
-				 * we drop the lock, unless we take a
-				 * reference on it.
-				 */
-				userfaultfd_ctx_get(fork_nctx);
-				spin_unlock(&ctx->event_wqh.lock);
-				ret = 0;
-				break;
-			}
-
-			userfaultfd_event_complete(ctx, uwq);
-			spin_unlock(&ctx->event_wqh.lock);
-			ret = 0;
-			break;
-		}
-		spin_unlock(&ctx->event_wqh.lock);
-
-		if (signal_pending(current)) {
-			ret = -ERESTARTSYS;
-			break;
-		}
-		if (no_wait) {
-			ret = -EAGAIN;
-			break;
-		}
-		spin_unlock_irq(&ctx->fd_wqh.lock);
-		schedule();
-		spin_lock_irq(&ctx->fd_wqh.lock);
-	}
-	__remove_wait_queue(&ctx->fd_wqh, &wait);
-	__set_current_state(TASK_RUNNING);
-	spin_unlock_irq(&ctx->fd_wqh.lock);
-
-	if (!ret && msg->event == UFFD_EVENT_FORK) {
-		ret = resolve_userfault_fork(fork_nctx, inode, msg);
-		spin_lock_irq(&ctx->event_wqh.lock);
-		if (!list_empty(&fork_event)) {
-			/*
-			 * The fork thread didn't abort, so we can
-			 * drop the temporary refcount.
-			 */
-			userfaultfd_ctx_put(fork_nctx);
-
-			uwq = list_first_entry(&fork_event,
-					       typeof(*uwq),
-					       wq.entry);
-			/*
-			 * If fork_event list wasn't empty and in turn
-			 * the event wasn't already released by fork
-			 * (the event is allocated on fork kernel
-			 * stack), put the event back to its place in
-			 * the event_wq. fork_event head will be freed
-			 * as soon as we return so the event cannot
-			 * stay queued there no matter the current
-			 * "ret" value.
-			 */
-			list_del(&uwq->wq.entry);
-			__add_wait_queue(&ctx->event_wqh, &uwq->wq);
-
-			/*
-			 * Leave the event in the waitqueue and report
-			 * error to userland if we failed to resolve
-			 * the userfault fork.
-			 */
-			if (likely(!ret))
-				userfaultfd_event_complete(ctx, uwq);
-		} else {
-			/*
-			 * Here the fork thread aborted and the
-			 * refcount from the fork thread on fork_nctx
-			 * has already been released. We still hold
-			 * the reference we took before releasing the
-			 * lock above. If resolve_userfault_fork
-			 * failed we've to drop it because the
-			 * fork_nctx has to be freed in such case. If
-			 * it succeeded we'll hold it because the new
-			 * uffd references it.
-			 */
-			if (ret)
-				userfaultfd_ctx_put(fork_nctx);
-		}
-		spin_unlock_irq(&ctx->event_wqh.lock);
-	}
-
-	return ret;
-}
-
-static ssize_t userfaultfd_read_iter(struct kiocb *iocb, struct iov_iter *to)
-{
-	struct file *file = iocb->ki_filp;
-	struct userfaultfd_ctx *ctx = file->private_data;
-	ssize_t _ret, ret = 0;
-	struct uffd_msg msg;
-	struct inode *inode = file_inode(file);
-	bool no_wait;
-
-	if (!userfaultfd_is_initialized(ctx))
-		return -EINVAL;
-
-	no_wait = file->f_flags & O_NONBLOCK || iocb->ki_flags & IOCB_NOWAIT;
-	for (;;) {
-		if (iov_iter_count(to) < sizeof(msg))
-			return ret ? ret : -EINVAL;
-		_ret = userfaultfd_ctx_read(ctx, no_wait, &msg, inode);
-		if (_ret < 0)
-			return ret ? ret : _ret;
-		_ret = !copy_to_iter_full(&msg, sizeof(msg), to);
-		if (_ret)
-			return ret ? ret : -EFAULT;
-		ret += sizeof(msg);
-		/*
-		 * Allow to read more than one fault at time but only
-		 * block if waiting for the very first one.
-		 */
-		no_wait = true;
-	}
-}
-
-static void __wake_userfault(struct userfaultfd_ctx *ctx,
-			     struct userfaultfd_wake_range *range)
-{
-	spin_lock_irq(&ctx->fault_pending_wqh.lock);
-	/* wake all in the range and autoremove */
-	if (waitqueue_active(&ctx->fault_pending_wqh))
-		__wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL,
-				     range);
-	if (waitqueue_active(&ctx->fault_wqh))
-		__wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, range);
-	spin_unlock_irq(&ctx->fault_pending_wqh.lock);
-}
-
-static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx,
-					   struct userfaultfd_wake_range *range)
-{
-	unsigned seq;
-	bool need_wakeup;
-
-	/*
-	 * To be sure waitqueue_active() is not reordered by the CPU
-	 * before the pagetable update, use an explicit SMP memory
-	 * barrier here. PT lock release or mmap_read_unlock(mm) still
-	 * have release semantics that can allow the
-	 * waitqueue_active() to be reordered before the pte update.
-	 */
-	smp_mb();
-
-	/*
-	 * Use waitqueue_active because it's very frequent to
-	 * change the address space atomically even if there are no
-	 * userfaults yet. So we take the spinlock only when we're
-	 * sure we've userfaults to wake.
-	 */
-	do {
-		seq = read_seqcount_begin(&ctx->refile_seq);
-		need_wakeup = waitqueue_active(&ctx->fault_pending_wqh) ||
-			waitqueue_active(&ctx->fault_wqh);
-		cond_resched();
-	} while (read_seqcount_retry(&ctx->refile_seq, seq));
-	if (need_wakeup)
-		__wake_userfault(ctx, range);
-}
-
-static __always_inline int validate_unaligned_range(
-	struct mm_struct *mm, __u64 start, __u64 len)
-{
-	__u64 task_size = mm->task_size;
-
-	if (len & ~PAGE_MASK)
-		return -EINVAL;
-	if (!len)
-		return -EINVAL;
-	if (start >= task_size)
-		return -EINVAL;
-	if (len > task_size - start)
-		return -EINVAL;
-	if (start + len <= start)
-		return -EINVAL;
-	return 0;
-}
-
-static __always_inline int validate_range(struct mm_struct *mm,
-					  __u64 start, __u64 len)
-{
-	if (start & ~PAGE_MASK)
-		return -EINVAL;
-
-	return validate_unaligned_range(mm, start, len);
-}
-
-static int userfaultfd_register(struct userfaultfd_ctx *ctx,
-				unsigned long arg)
-{
-	struct mm_struct *mm = ctx->mm;
-	struct vm_area_struct *vma, *cur;
-	int ret;
-	struct uffdio_register uffdio_register;
-	struct uffdio_register __user *user_uffdio_register;
-	vm_flags_t vm_flags;
-	bool found;
-	bool basic_ioctls;
-	unsigned long start, end;
-	struct vma_iterator vmi;
-	bool wp_async = userfaultfd_wp_async_ctx(ctx);
-
-	user_uffdio_register = (struct uffdio_register __user *) arg;
-
-	ret = -EFAULT;
-	if (copy_from_user(&uffdio_register, user_uffdio_register,
-			   sizeof(uffdio_register)-sizeof(__u64)))
-		goto out;
-
-	ret = -EINVAL;
-	if (!uffdio_register.mode)
-		goto out;
-	if (uffdio_register.mode & ~UFFD_API_REGISTER_MODES)
-		goto out;
-	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 (!pgtable_supports_uffd_wp())
-			goto out;
-
-		vm_flags |= VM_UFFD_WP;
-	}
-	if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR) {
-#ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
-		goto out;
-#endif
-		vm_flags |= VM_UFFD_MINOR;
-	}
-
-	ret = validate_range(mm, uffdio_register.range.start,
-			     uffdio_register.range.len);
-	if (ret)
-		goto out;
-
-	start = uffdio_register.range.start;
-	end = start + uffdio_register.range.len;
-
-	ret = -ENOMEM;
-	if (!mmget_not_zero(mm))
-		goto out;
-
-	ret = -EINVAL;
-	mmap_write_lock(mm);
-	vma_iter_init(&vmi, mm, start);
-	vma = vma_find(&vmi, end);
-	if (!vma)
-		goto out_unlock;
-
-	/*
-	 * If the first vma contains huge pages, make sure start address
-	 * is aligned to huge page size.
-	 */
-	if (is_vm_hugetlb_page(vma)) {
-		unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
-
-		if (start & (vma_hpagesize - 1))
-			goto out_unlock;
-	}
-
-	/*
-	 * Search for not compatible vmas.
-	 */
-	found = false;
-	basic_ioctls = false;
-	cur = vma;
-	do {
-		cond_resched();
-
-		VM_WARN_ON_ONCE(!!cur->vm_userfaultfd_ctx.ctx ^
-				!!(cur->vm_flags & __VM_UFFD_FLAGS));
-
-		/* check not compatible vmas */
-		ret = -EINVAL;
-		if (!vma_can_userfault(cur, vm_flags, wp_async))
-			goto out_unlock;
-
-		/*
-		 * UFFDIO_COPY will fill file holes even without
-		 * PROT_WRITE. This check enforces that if this is a
-		 * MAP_SHARED, the process has write permission to the backing
-		 * file. If VM_MAYWRITE is set it also enforces that on a
-		 * MAP_SHARED vma: there is no F_WRITE_SEAL and no further
-		 * F_WRITE_SEAL can be taken until the vma is destroyed.
-		 */
-		ret = -EPERM;
-		if (unlikely(!(cur->vm_flags & VM_MAYWRITE)))
-			goto out_unlock;
-
-		/*
-		 * If this vma contains ending address, and huge pages
-		 * check alignment.
-		 */
-		if (is_vm_hugetlb_page(cur) && end <= cur->vm_end &&
-		    end > cur->vm_start) {
-			unsigned long vma_hpagesize = vma_kernel_pagesize(cur);
-
-			ret = -EINVAL;
-
-			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
-		 * different userfaultfd. We can't allow more than one
-		 * userfaultfd to own a single vma simultaneously or we
-		 * wouldn't know which one to deliver the userfaults to.
-		 */
-		ret = -EBUSY;
-		if (cur->vm_userfaultfd_ctx.ctx &&
-		    cur->vm_userfaultfd_ctx.ctx != ctx)
-			goto out_unlock;
-
-		/*
-		 * Note vmas containing huge pages
-		 */
-		if (is_vm_hugetlb_page(cur))
-			basic_ioctls = true;
-
-		found = true;
-	} for_each_vma_range(vmi, cur, end);
-	VM_WARN_ON_ONCE(!found);
-
-	ret = userfaultfd_register_range(ctx, vma, vm_flags, start, end,
-					 wp_async);
-
-out_unlock:
-	mmap_write_unlock(mm);
-	mmput(mm);
-	if (!ret) {
-		__u64 ioctls_out;
-
-		ioctls_out = basic_ioctls ? UFFD_API_RANGE_IOCTLS_BASIC :
-		    UFFD_API_RANGE_IOCTLS;
-
-		/*
-		 * Declare the WP ioctl only if the WP mode is
-		 * specified and all checks passed with the range
-		 */
-		if (!(uffdio_register.mode & UFFDIO_REGISTER_MODE_WP))
-			ioctls_out &= ~((__u64)1 << _UFFDIO_WRITEPROTECT);
-
-		/* CONTINUE ioctl is only supported for MINOR ranges. */
-		if (!(uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR))
-			ioctls_out &= ~((__u64)1 << _UFFDIO_CONTINUE);
-
-		/*
-		 * Now that we scanned all vmas we can already tell
-		 * userland which ioctls methods are guaranteed to
-		 * succeed on this range.
-		 */
-		if (put_user(ioctls_out, &user_uffdio_register->ioctls))
-			ret = -EFAULT;
-	}
-out:
-	return ret;
-}
-
-static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
-				  unsigned long arg)
-{
-	struct mm_struct *mm = ctx->mm;
-	struct vm_area_struct *vma, *prev, *cur;
-	int ret;
-	struct uffdio_range uffdio_unregister;
-	bool found;
-	unsigned long start, end, vma_end;
-	const void __user *buf = (void __user *)arg;
-	struct vma_iterator vmi;
-	bool wp_async = userfaultfd_wp_async_ctx(ctx);
-
-	ret = -EFAULT;
-	if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister)))
-		goto out;
-
-	ret = validate_range(mm, uffdio_unregister.start,
-			     uffdio_unregister.len);
-	if (ret)
-		goto out;
-
-	start = uffdio_unregister.start;
-	end = start + uffdio_unregister.len;
-
-	ret = -ENOMEM;
-	if (!mmget_not_zero(mm))
-		goto out;
-
-	mmap_write_lock(mm);
-	ret = -EINVAL;
-	vma_iter_init(&vmi, mm, start);
-	vma = vma_find(&vmi, end);
-	if (!vma)
-		goto out_unlock;
-
-	/*
-	 * If the first vma contains huge pages, make sure start address
-	 * is aligned to huge page size.
-	 */
-	if (is_vm_hugetlb_page(vma)) {
-		unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
-
-		if (start & (vma_hpagesize - 1))
-			goto out_unlock;
-	}
-
-	/*
-	 * Search for not compatible vmas.
-	 */
-	found = false;
-	cur = vma;
-	do {
-		cond_resched();
-
-		VM_WARN_ON_ONCE(!!cur->vm_userfaultfd_ctx.ctx ^
-				!!(cur->vm_flags & __VM_UFFD_FLAGS));
-
-		/*
-		 * Prevent unregistering through a different userfaultfd than
-		 * the one used for registration.
-		 */
-		if (cur->vm_userfaultfd_ctx.ctx &&
-		    cur->vm_userfaultfd_ctx.ctx != ctx)
-			goto out_unlock;
-
-		/*
-		 * Check not compatible vmas, not strictly required
-		 * here as not compatible vmas cannot have an
-		 * userfaultfd_ctx registered on them, but this
-		 * provides for more strict behavior to notice
-		 * unregistration errors.
-		 */
-		if (!vma_can_userfault(cur, cur->vm_flags, wp_async))
-			goto out_unlock;
-
-		found = true;
-	} for_each_vma_range(vmi, cur, end);
-	VM_WARN_ON_ONCE(!found);
-
-	vma_iter_set(&vmi, start);
-	prev = vma_prev(&vmi);
-	if (vma->vm_start < start)
-		prev = vma;
-
-	ret = 0;
-	for_each_vma_range(vmi, vma, end) {
-		cond_resched();
-
-		/* VMA not registered with userfaultfd. */
-		if (!vma->vm_userfaultfd_ctx.ctx)
-			goto skip;
-
-		VM_WARN_ON_ONCE(vma->vm_userfaultfd_ctx.ctx != ctx);
-		VM_WARN_ON_ONCE(!vma_can_userfault(vma, vma->vm_flags, wp_async));
-		VM_WARN_ON_ONCE(!(vma->vm_flags & VM_MAYWRITE));
-
-		if (vma->vm_start > start)
-			start = vma->vm_start;
-		vma_end = min(end, vma->vm_end);
-
-		if (userfaultfd_missing(vma)) {
-			/*
-			 * Wake any concurrent pending userfault while
-			 * we unregister, so they will not hang
-			 * permanently and it avoids userland to call
-			 * UFFDIO_WAKE explicitly.
-			 */
-			struct userfaultfd_wake_range range;
-			range.start = start;
-			range.len = vma_end - start;
-			wake_userfault(vma->vm_userfaultfd_ctx.ctx, &range);
-		}
-
-		vma = userfaultfd_clear_vma(&vmi, prev, vma,
-					    start, vma_end);
-		if (IS_ERR(vma)) {
-			ret = PTR_ERR(vma);
-			break;
-		}
-
-	skip:
-		prev = vma;
-		start = vma->vm_end;
-	}
-
-out_unlock:
-	mmap_write_unlock(mm);
-	mmput(mm);
-out:
-	return ret;
-}
-
-/*
- * userfaultfd_wake may be used in combination with the
- * UFFDIO_*_MODE_DONTWAKE to wakeup userfaults in batches.
- */
-static int userfaultfd_wake(struct userfaultfd_ctx *ctx,
-			    unsigned long arg)
-{
-	int ret;
-	struct uffdio_range uffdio_wake;
-	struct userfaultfd_wake_range range;
-	const void __user *buf = (void __user *)arg;
-
-	ret = -EFAULT;
-	if (copy_from_user(&uffdio_wake, buf, sizeof(uffdio_wake)))
-		goto out;
-
-	ret = validate_range(ctx->mm, uffdio_wake.start, uffdio_wake.len);
-	if (ret)
-		goto out;
-
-	range.start = uffdio_wake.start;
-	range.len = uffdio_wake.len;
-
-	/*
-	 * len == 0 means wake all and we don't want to wake all here,
-	 * so check it again to be sure.
-	 */
-	VM_WARN_ON_ONCE(!range.len);
-
-	wake_userfault(ctx, &range);
-	ret = 0;
-
-out:
-	return ret;
-}
-
-static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
-			    unsigned long arg)
-{
-	__s64 ret;
-	struct uffdio_copy uffdio_copy;
-	struct uffdio_copy __user *user_uffdio_copy;
-	struct userfaultfd_wake_range range;
-	uffd_flags_t flags = 0;
-
-	user_uffdio_copy = (struct uffdio_copy __user *) arg;
-
-	ret = -EAGAIN;
-	if (unlikely(atomic_read(&ctx->mmap_changing))) {
-		if (unlikely(put_user(ret, &user_uffdio_copy->copy)))
-			return -EFAULT;
-		goto out;
-	}
-
-	ret = -EFAULT;
-	if (copy_from_user(&uffdio_copy, user_uffdio_copy,
-			   /* don't copy "copy" last field */
-			   sizeof(uffdio_copy)-sizeof(__s64)))
-		goto out;
-
-	ret = validate_unaligned_range(ctx->mm, uffdio_copy.src,
-				       uffdio_copy.len);
-	if (ret)
-		goto out;
-	ret = validate_range(ctx->mm, uffdio_copy.dst, uffdio_copy.len);
-	if (ret)
-		goto out;
-
-	ret = -EINVAL;
-	if (uffdio_copy.mode & ~(UFFDIO_COPY_MODE_DONTWAKE|UFFDIO_COPY_MODE_WP))
-		goto out;
-	if (uffdio_copy.mode & UFFDIO_COPY_MODE_WP)
-		flags |= MFILL_ATOMIC_WP;
-	if (mmget_not_zero(ctx->mm)) {
-		ret = mfill_atomic_copy(ctx, uffdio_copy.dst, uffdio_copy.src,
-					uffdio_copy.len, flags);
-		mmput(ctx->mm);
-	} else {
-		return -ESRCH;
-	}
-	if (unlikely(put_user(ret, &user_uffdio_copy->copy)))
-		return -EFAULT;
-	if (ret < 0)
-		goto out;
-	VM_WARN_ON_ONCE(!ret);
-	/* len == 0 would wake all */
-	range.len = ret;
-	if (!(uffdio_copy.mode & UFFDIO_COPY_MODE_DONTWAKE)) {
-		range.start = uffdio_copy.dst;
-		wake_userfault(ctx, &range);
-	}
-	ret = range.len == uffdio_copy.len ? 0 : -EAGAIN;
-out:
-	return ret;
-}
-
-static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx,
-				unsigned long arg)
-{
-	__s64 ret;
-	struct uffdio_zeropage uffdio_zeropage;
-	struct uffdio_zeropage __user *user_uffdio_zeropage;
-	struct userfaultfd_wake_range range;
-
-	user_uffdio_zeropage = (struct uffdio_zeropage __user *) arg;
-
-	ret = -EAGAIN;
-	if (unlikely(atomic_read(&ctx->mmap_changing))) {
-		if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage)))
-			return -EFAULT;
-		goto out;
-	}
-
-	ret = -EFAULT;
-	if (copy_from_user(&uffdio_zeropage, user_uffdio_zeropage,
-			   /* don't copy "zeropage" last field */
-			   sizeof(uffdio_zeropage)-sizeof(__s64)))
-		goto out;
-
-	ret = validate_range(ctx->mm, uffdio_zeropage.range.start,
-			     uffdio_zeropage.range.len);
-	if (ret)
-		goto out;
-	ret = -EINVAL;
-	if (uffdio_zeropage.mode & ~UFFDIO_ZEROPAGE_MODE_DONTWAKE)
-		goto out;
-
-	if (mmget_not_zero(ctx->mm)) {
-		ret = mfill_atomic_zeropage(ctx, uffdio_zeropage.range.start,
-					   uffdio_zeropage.range.len);
-		mmput(ctx->mm);
-	} else {
-		return -ESRCH;
-	}
-	if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage)))
-		return -EFAULT;
-	if (ret < 0)
-		goto out;
-	/* len == 0 would wake all */
-	VM_WARN_ON_ONCE(!ret);
-	range.len = ret;
-	if (!(uffdio_zeropage.mode & UFFDIO_ZEROPAGE_MODE_DONTWAKE)) {
-		range.start = uffdio_zeropage.range.start;
-		wake_userfault(ctx, &range);
-	}
-	ret = range.len == uffdio_zeropage.range.len ? 0 : -EAGAIN;
-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;
-	bool mode_wp, mode_dontwake;
-
-	if (atomic_read(&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;
-
-	mode_wp = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_WP;
-	mode_dontwake = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_DONTWAKE;
-
-	if (mode_wp && mode_dontwake)
-		return -EINVAL;
-
-	if (mmget_not_zero(ctx->mm)) {
-		ret = mwriteprotect_range(ctx, uffdio_wp.range.start,
-					  uffdio_wp.range.len, mode_wp);
-		mmput(ctx->mm);
-	} else {
-		return -ESRCH;
-	}
-
-	if (ret)
-		return ret;
-
-	if (!mode_wp && !mode_dontwake) {
-		range.start = uffdio_wp.range.start;
-		range.len = uffdio_wp.range.len;
-		wake_userfault(ctx, &range);
-	}
-	return ret;
-}
-
-static int userfaultfd_continue(struct userfaultfd_ctx *ctx, unsigned long arg)
-{
-	__s64 ret;
-	struct uffdio_continue uffdio_continue;
-	struct uffdio_continue __user *user_uffdio_continue;
-	struct userfaultfd_wake_range range;
-	uffd_flags_t flags = 0;
-
-	user_uffdio_continue = (struct uffdio_continue __user *)arg;
-
-	ret = -EAGAIN;
-	if (unlikely(atomic_read(&ctx->mmap_changing))) {
-		if (unlikely(put_user(ret, &user_uffdio_continue->mapped)))
-			return -EFAULT;
-		goto out;
-	}
-
-	ret = -EFAULT;
-	if (copy_from_user(&uffdio_continue, user_uffdio_continue,
-			   /* don't copy the output fields */
-			   sizeof(uffdio_continue) - (sizeof(__s64))))
-		goto out;
-
-	ret = validate_range(ctx->mm, uffdio_continue.range.start,
-			     uffdio_continue.range.len);
-	if (ret)
-		goto out;
-
-	ret = -EINVAL;
-	if (uffdio_continue.mode & ~(UFFDIO_CONTINUE_MODE_DONTWAKE |
-				     UFFDIO_CONTINUE_MODE_WP))
-		goto out;
-	if (uffdio_continue.mode & UFFDIO_CONTINUE_MODE_WP)
-		flags |= MFILL_ATOMIC_WP;
-
-	if (mmget_not_zero(ctx->mm)) {
-		ret = mfill_atomic_continue(ctx, uffdio_continue.range.start,
-					    uffdio_continue.range.len, flags);
-		mmput(ctx->mm);
-	} else {
-		return -ESRCH;
-	}
-
-	if (unlikely(put_user(ret, &user_uffdio_continue->mapped)))
-		return -EFAULT;
-	if (ret < 0)
-		goto out;
-
-	/* len == 0 would wake all */
-	VM_WARN_ON_ONCE(!ret);
-	range.len = ret;
-	if (!(uffdio_continue.mode & UFFDIO_CONTINUE_MODE_DONTWAKE)) {
-		range.start = uffdio_continue.range.start;
-		wake_userfault(ctx, &range);
-	}
-	ret = range.len == uffdio_continue.range.len ? 0 : -EAGAIN;
-
-out:
-	return ret;
-}
-
-static inline int userfaultfd_poison(struct userfaultfd_ctx *ctx, unsigned long arg)
-{
-	__s64 ret;
-	struct uffdio_poison uffdio_poison;
-	struct uffdio_poison __user *user_uffdio_poison;
-	struct userfaultfd_wake_range range;
-
-	user_uffdio_poison = (struct uffdio_poison __user *)arg;
-
-	ret = -EAGAIN;
-	if (unlikely(atomic_read(&ctx->mmap_changing))) {
-		if (unlikely(put_user(ret, &user_uffdio_poison->updated)))
-			return -EFAULT;
-		goto out;
-	}
-
-	ret = -EFAULT;
-	if (copy_from_user(&uffdio_poison, user_uffdio_poison,
-			   /* don't copy the output fields */
-			   sizeof(uffdio_poison) - (sizeof(__s64))))
-		goto out;
-
-	ret = validate_range(ctx->mm, uffdio_poison.range.start,
-			     uffdio_poison.range.len);
-	if (ret)
-		goto out;
-
-	ret = -EINVAL;
-	if (uffdio_poison.mode & ~UFFDIO_POISON_MODE_DONTWAKE)
-		goto out;
-
-	if (mmget_not_zero(ctx->mm)) {
-		ret = mfill_atomic_poison(ctx, uffdio_poison.range.start,
-					  uffdio_poison.range.len, 0);
-		mmput(ctx->mm);
-	} else {
-		return -ESRCH;
-	}
-
-	if (unlikely(put_user(ret, &user_uffdio_poison->updated)))
-		return -EFAULT;
-	if (ret < 0)
-		goto out;
-
-	/* len == 0 would wake all */
-	VM_WARN_ON_ONCE(!ret);
-	range.len = ret;
-	if (!(uffdio_poison.mode & UFFDIO_POISON_MODE_DONTWAKE)) {
-		range.start = uffdio_poison.range.start;
-		wake_userfault(ctx, &range);
-	}
-	ret = range.len == uffdio_poison.range.len ? 0 : -EAGAIN;
-
-out:
-	return ret;
-}
-
-bool userfaultfd_wp_async(struct vm_area_struct *vma)
-{
-	return userfaultfd_wp_async_ctx(vma->vm_userfaultfd_ctx.ctx);
-}
-
-static inline unsigned int uffd_ctx_features(__u64 user_features)
-{
-	/*
-	 * For the current set of features the bits just coincide. Set
-	 * UFFD_FEATURE_INITIALIZED to mark the features as enabled.
-	 */
-	return (unsigned int)user_features | UFFD_FEATURE_INITIALIZED;
-}
-
-static int userfaultfd_move(struct userfaultfd_ctx *ctx,
-			    unsigned long arg)
-{
-	__s64 ret;
-	struct uffdio_move uffdio_move;
-	struct uffdio_move __user *user_uffdio_move;
-	struct userfaultfd_wake_range range;
-	struct mm_struct *mm = ctx->mm;
-
-	user_uffdio_move = (struct uffdio_move __user *) arg;
-
-	ret = -EAGAIN;
-	if (unlikely(atomic_read(&ctx->mmap_changing))) {
-		if (unlikely(put_user(ret, &user_uffdio_move->move)))
-			return -EFAULT;
-		goto out;
-	}
-
-	if (copy_from_user(&uffdio_move, user_uffdio_move,
-			   /* don't copy "move" last field */
-			   sizeof(uffdio_move)-sizeof(__s64)))
-		return -EFAULT;
-
-	/* Do not allow cross-mm moves. */
-	if (mm != current->mm)
-		return -EINVAL;
-
-	ret = validate_range(mm, uffdio_move.dst, uffdio_move.len);
-	if (ret)
-		return ret;
-
-	ret = validate_range(mm, uffdio_move.src, uffdio_move.len);
-	if (ret)
-		return ret;
-
-	if (uffdio_move.mode & ~(UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES|
-				  UFFDIO_MOVE_MODE_DONTWAKE))
-		return -EINVAL;
-
-	if (mmget_not_zero(mm)) {
-		ret = move_pages(ctx, uffdio_move.dst, uffdio_move.src,
-				 uffdio_move.len, uffdio_move.mode);
-		mmput(mm);
-	} else {
-		return -ESRCH;
-	}
-
-	if (unlikely(put_user(ret, &user_uffdio_move->move)))
-		return -EFAULT;
-	if (ret < 0)
-		goto out;
-
-	/* len == 0 would wake all */
-	VM_WARN_ON(!ret);
-	range.len = ret;
-	if (!(uffdio_move.mode & UFFDIO_MOVE_MODE_DONTWAKE)) {
-		range.start = uffdio_move.dst;
-		wake_userfault(ctx, &range);
-	}
-	ret = range.len == uffdio_move.len ? 0 : -EAGAIN;
-
-out:
-	return ret;
-}
-
-/*
- * userland asks for a certain API version and we return which bits
- * and ioctl commands are implemented in this kernel for such API
- * version or -EINVAL if unknown.
- */
-static int userfaultfd_api(struct userfaultfd_ctx *ctx,
-			   unsigned long arg)
-{
-	struct uffdio_api uffdio_api;
-	void __user *buf = (void __user *)arg;
-	unsigned int ctx_features;
-	int ret;
-	__u64 features;
-
-	ret = -EFAULT;
-	if (copy_from_user(&uffdio_api, buf, sizeof(uffdio_api)))
-		goto out;
-	features = uffdio_api.features;
-	ret = -EINVAL;
-	if (uffdio_api.api != UFFD_API)
-		goto err_out;
-	ret = -EPERM;
-	if ((features & UFFD_FEATURE_EVENT_FORK) && !capable(CAP_SYS_PTRACE))
-		goto err_out;
-
-	/* WP_ASYNC relies on WP_UNPOPULATED, choose it unconditionally */
-	if (features & UFFD_FEATURE_WP_ASYNC)
-		features |= UFFD_FEATURE_WP_UNPOPULATED;
-
-	/* report all available features and ioctls to userland */
-	uffdio_api.features = UFFD_API_FEATURES;
-#ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
-	uffdio_api.features &=
-		~(UFFD_FEATURE_MINOR_HUGETLBFS | UFFD_FEATURE_MINOR_SHMEM);
-#endif
-	if (!pgtable_supports_uffd_wp())
-		uffdio_api.features &= ~UFFD_FEATURE_PAGEFAULT_FLAG_WP;
-
-	if (!uffd_supports_wp_marker()) {
-		uffdio_api.features &= ~UFFD_FEATURE_WP_HUGETLBFS_SHMEM;
-		uffdio_api.features &= ~UFFD_FEATURE_WP_UNPOPULATED;
-		uffdio_api.features &= ~UFFD_FEATURE_WP_ASYNC;
-	}
-
-	ret = -EINVAL;
-	if (features & ~uffdio_api.features)
-		goto err_out;
-
-	uffdio_api.ioctls = UFFD_API_IOCTLS;
-	ret = -EFAULT;
-	if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
-		goto out;
-
-	/* only enable the requested features for this uffd context */
-	ctx_features = uffd_ctx_features(features);
-	ret = -EINVAL;
-	if (cmpxchg(&ctx->features, 0, ctx_features) != 0)
-		goto err_out;
-
-	ret = 0;
-out:
-	return ret;
-err_out:
-	memset(&uffdio_api, 0, sizeof(uffdio_api));
-	if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
-		ret = -EFAULT;
-	goto out;
-}
-
-static long userfaultfd_ioctl(struct file *file, unsigned cmd,
-			      unsigned long arg)
-{
-	int ret = -EINVAL;
-	struct userfaultfd_ctx *ctx = file->private_data;
-
-	if (cmd != UFFDIO_API && !userfaultfd_is_initialized(ctx))
-		return -EINVAL;
-
-	switch(cmd) {
-	case UFFDIO_API:
-		ret = userfaultfd_api(ctx, arg);
-		break;
-	case UFFDIO_REGISTER:
-		ret = userfaultfd_register(ctx, arg);
-		break;
-	case UFFDIO_UNREGISTER:
-		ret = userfaultfd_unregister(ctx, arg);
-		break;
-	case UFFDIO_WAKE:
-		ret = userfaultfd_wake(ctx, arg);
-		break;
-	case UFFDIO_COPY:
-		ret = userfaultfd_copy(ctx, arg);
-		break;
-	case UFFDIO_ZEROPAGE:
-		ret = userfaultfd_zeropage(ctx, arg);
-		break;
-	case UFFDIO_MOVE:
-		ret = userfaultfd_move(ctx, arg);
-		break;
-	case UFFDIO_WRITEPROTECT:
-		ret = userfaultfd_writeprotect(ctx, arg);
-		break;
-	case UFFDIO_CONTINUE:
-		ret = userfaultfd_continue(ctx, arg);
-		break;
-	case UFFDIO_POISON:
-		ret = userfaultfd_poison(ctx, arg);
-		break;
-	}
-	return ret;
-}
-
-#ifdef CONFIG_PROC_FS
-static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f)
-{
-	struct userfaultfd_ctx *ctx = f->private_data;
-	wait_queue_entry_t *wq;
-	unsigned long pending = 0, total = 0;
-
-	spin_lock_irq(&ctx->fault_pending_wqh.lock);
-	list_for_each_entry(wq, &ctx->fault_pending_wqh.head, entry) {
-		pending++;
-		total++;
-	}
-	list_for_each_entry(wq, &ctx->fault_wqh.head, entry) {
-		total++;
-	}
-	spin_unlock_irq(&ctx->fault_pending_wqh.lock);
-
-	/*
-	 * If more protocols will be added, there will be all shown
-	 * separated by a space. Like this:
-	 *	protocols: aa:... bb:...
-	 */
-	seq_printf(m, "pending:\t%lu\ntotal:\t%lu\nAPI:\t%Lx:%x:%Lx\n",
-		   pending, total, UFFD_API, ctx->features,
-		   UFFD_API_IOCTLS|UFFD_API_RANGE_IOCTLS);
-}
-#endif
-
-static const struct file_operations userfaultfd_fops = {
-#ifdef CONFIG_PROC_FS
-	.show_fdinfo	= userfaultfd_show_fdinfo,
-#endif
-	.release	= userfaultfd_release,
-	.poll		= userfaultfd_poll,
-	.read_iter	= userfaultfd_read_iter,
-	.unlocked_ioctl = userfaultfd_ioctl,
-	.compat_ioctl	= compat_ptr_ioctl,
-	.llseek		= noop_llseek,
-};
-
-static void init_once_userfaultfd_ctx(void *mem)
-{
-	struct userfaultfd_ctx *ctx = (struct userfaultfd_ctx *) mem;
-
-	init_waitqueue_head(&ctx->fault_pending_wqh);
-	init_waitqueue_head(&ctx->fault_wqh);
-	init_waitqueue_head(&ctx->event_wqh);
-	init_waitqueue_head(&ctx->fd_wqh);
-	seqcount_spinlock_init(&ctx->refile_seq, &ctx->fault_pending_wqh.lock);
-}
-
-static int new_userfaultfd(int flags)
-{
-	struct userfaultfd_ctx *ctx __free(kfree) = NULL;
-
-	VM_WARN_ON_ONCE(!current->mm);
-
-	/* Check the UFFD_* constants for consistency.  */
-	BUILD_BUG_ON(UFFD_USER_MODE_ONLY & UFFD_SHARED_FCNTL_FLAGS);
-
-	if (flags & ~(UFFD_SHARED_FCNTL_FLAGS | UFFD_USER_MODE_ONLY))
-		return -EINVAL;
-
-	ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
-	if (!ctx)
-		return -ENOMEM;
-
-	refcount_set(&ctx->refcount, 1);
-	ctx->flags = flags;
-	ctx->features = 0;
-	ctx->released = false;
-	init_rwsem(&ctx->map_changing_lock);
-	atomic_set(&ctx->mmap_changing, 0);
-	ctx->mm = current->mm;
-
-	FD_PREPARE(fdf, flags & UFFD_SHARED_FCNTL_FLAGS,
-		   anon_inode_create_getfile("[userfaultfd]", &userfaultfd_fops, ctx,
-					     O_RDONLY | (flags & UFFD_SHARED_FCNTL_FLAGS),
-					     NULL));
-	if (fdf.err)
-		return fdf.err;
-
-	/* prevent the mm struct to be freed */
-	mmgrab(ctx->mm);
-	fd_prepare_file(fdf)->f_mode |= FMODE_NOWAIT;
-	retain_and_null_ptr(ctx);
-	return fd_publish(fdf);
-}
-
-static inline bool userfaultfd_syscall_allowed(int flags)
-{
-	/* Userspace-only page faults are always allowed */
-	if (flags & UFFD_USER_MODE_ONLY)
-		return true;
-
-	/*
-	 * The user is requesting a userfaultfd which can handle kernel faults.
-	 * Privileged users are always allowed to do this.
-	 */
-	if (capable(CAP_SYS_PTRACE))
-		return true;
-
-	/* Otherwise, access to kernel fault handling is sysctl controlled. */
-	return sysctl_unprivileged_userfaultfd;
-}
-
-SYSCALL_DEFINE1(userfaultfd, int, flags)
-{
-	if (!userfaultfd_syscall_allowed(flags))
-		return -EPERM;
-
-	return new_userfaultfd(flags);
-}
-
-static long userfaultfd_dev_ioctl(struct file *file, unsigned int cmd, unsigned long flags)
-{
-	if (cmd != USERFAULTFD_IOC_NEW)
-		return -EINVAL;
-
-	return new_userfaultfd(flags);
-}
-
-static const struct file_operations userfaultfd_dev_fops = {
-	.unlocked_ioctl = userfaultfd_dev_ioctl,
-	.compat_ioctl = userfaultfd_dev_ioctl,
-	.owner = THIS_MODULE,
-	.llseek = noop_llseek,
-};
-
-static struct miscdevice userfaultfd_misc = {
-	.minor = MISC_DYNAMIC_MINOR,
-	.name = "userfaultfd",
-	.fops = &userfaultfd_dev_fops
-};
-
-static int __init userfaultfd_init(void)
-{
-	int ret;
-
-	ret = misc_register(&userfaultfd_misc);
-	if (ret)
-		return ret;
-
-	userfaultfd_ctx_cachep = kmem_cache_create("userfaultfd_ctx_cache",
-						sizeof(struct userfaultfd_ctx),
-						0,
-						SLAB_HWCACHE_ALIGN|SLAB_PANIC,
-						init_once_userfaultfd_ctx);
-#ifdef CONFIG_SYSCTL
-	register_sysctl_init("vm", vm_userfaultfd_table);
-#endif
-	return 0;
-}
-__initcall(userfaultfd_init);
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 885da1e56466..d0cf44aec1c4 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -2,7 +2,12 @@
 /*
  *  mm/userfaultfd.c
  *
+ *  Copyright (C) 2007  Davide Libenzi <davidel@xmailserver.org>
+ *  Copyright (C) 2008-2009 Red Hat, Inc.
  *  Copyright (C) 2015  Red Hat, Inc.
+ *
+ *  Some part derived from fs/eventfd.c (anon inode setup) and
+ *  mm/ksm.c (mm hashing).
  */
 
 #include <linux/mm.h>
@@ -14,6 +19,18 @@
 #include <linux/userfaultfd_k.h>
 #include <linux/mmu_notifier.h>
 #include <linux/hugetlb.h>
+#include <linux/list.h>
+#include <linux/sched/mm.h>
+#include <linux/mm_inline.h>
+#include <linux/poll.h>
+#include <linux/slab.h>
+#include <linux/seq_file.h>
+#include <linux/file.h>
+#include <linux/bug.h>
+#include <linux/anon_inodes.h>
+#include <linux/syscalls.h>
+#include <linux/miscdevice.h>
+#include <linux/uio.h>
 #include <asm/tlbflush.h>
 #include <asm/tlb.h>
 #include "internal.h"
@@ -2229,3 +2246,2200 @@ void userfaultfd_release_all(struct mm_struct *mm,
 	mmap_write_unlock(mm);
 	mmput(mm);
 }
+
+static int sysctl_unprivileged_userfaultfd __read_mostly;
+
+#ifdef CONFIG_SYSCTL
+static const struct ctl_table vm_userfaultfd_table[] = {
+	{
+		.procname	= "unprivileged_userfaultfd",
+		.data		= &sysctl_unprivileged_userfaultfd,
+		.maxlen		= sizeof(sysctl_unprivileged_userfaultfd),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= SYSCTL_ZERO,
+		.extra2		= SYSCTL_ONE,
+	},
+};
+#endif
+
+static struct kmem_cache *userfaultfd_ctx_cachep __ro_after_init;
+
+struct userfaultfd_fork_ctx {
+	struct userfaultfd_ctx *orig;
+	struct userfaultfd_ctx *new;
+	struct list_head list;
+};
+
+struct userfaultfd_unmap_ctx {
+	struct userfaultfd_ctx *ctx;
+	unsigned long start;
+	unsigned long end;
+	struct list_head list;
+};
+
+struct userfaultfd_wait_queue {
+	struct uffd_msg msg;
+	wait_queue_entry_t wq;
+	struct userfaultfd_ctx *ctx;
+	bool waken;
+};
+
+struct userfaultfd_wake_range {
+	unsigned long start;
+	unsigned long len;
+};
+
+/* internal indication that UFFD_API ioctl was successfully executed */
+#define UFFD_FEATURE_INITIALIZED		(1u << 31)
+
+static bool userfaultfd_is_initialized(struct userfaultfd_ctx *ctx)
+{
+	return ctx->features & UFFD_FEATURE_INITIALIZED;
+}
+
+static bool userfaultfd_wp_async_ctx(struct userfaultfd_ctx *ctx)
+{
+	return ctx && (ctx->features & UFFD_FEATURE_WP_ASYNC);
+}
+
+/*
+ * Whether WP_UNPOPULATED is enabled on the uffd context.  It is only
+ * meaningful when userfaultfd_wp()==true on the vma and when it's
+ * anonymous.
+ */
+bool userfaultfd_wp_unpopulated(struct vm_area_struct *vma)
+{
+	struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx;
+
+	if (!ctx)
+		return false;
+
+	return ctx->features & UFFD_FEATURE_WP_UNPOPULATED;
+}
+
+static int userfaultfd_wake_function(wait_queue_entry_t *wq, unsigned mode,
+				     int wake_flags, void *key)
+{
+	struct userfaultfd_wake_range *range = key;
+	int ret;
+	struct userfaultfd_wait_queue *uwq;
+	unsigned long start, len;
+
+	uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
+	ret = 0;
+	/* len == 0 means wake all */
+	start = range->start;
+	len = range->len;
+	if (len && (start > uwq->msg.arg.pagefault.address ||
+		    start + len <= uwq->msg.arg.pagefault.address))
+		goto out;
+	WRITE_ONCE(uwq->waken, true);
+	/*
+	 * The Program-Order guarantees provided by the scheduler
+	 * ensure uwq->waken is visible before the task is woken.
+	 */
+	ret = wake_up_state(wq->private, mode);
+	if (ret) {
+		/*
+		 * Wake only once, autoremove behavior.
+		 *
+		 * After the effect of list_del_init is visible to the other
+		 * CPUs, the waitqueue may disappear from under us, see the
+		 * !list_empty_careful() in handle_userfault().
+		 *
+		 * try_to_wake_up() has an implicit smp_mb(), and the
+		 * wq->private is read before calling the extern function
+		 * "wake_up_state" (which in turns calls try_to_wake_up).
+		 */
+		list_del_init(&wq->entry);
+	}
+out:
+	return ret;
+}
+
+/**
+ * userfaultfd_ctx_get - Acquires a reference to the internal userfaultfd
+ * context.
+ * @ctx: [in] Pointer to the userfaultfd context.
+ */
+static void userfaultfd_ctx_get(struct userfaultfd_ctx *ctx)
+{
+	refcount_inc(&ctx->refcount);
+}
+
+/**
+ * userfaultfd_ctx_put - Releases a reference to the internal userfaultfd
+ * context.
+ * @ctx: [in] Pointer to userfaultfd context.
+ *
+ * The userfaultfd context reference must have been previously acquired either
+ * with userfaultfd_ctx_get() or userfaultfd_ctx_fdget().
+ */
+static void userfaultfd_ctx_put(struct userfaultfd_ctx *ctx)
+{
+	if (refcount_dec_and_test(&ctx->refcount)) {
+		VM_WARN_ON_ONCE(spin_is_locked(&ctx->fault_pending_wqh.lock));
+		VM_WARN_ON_ONCE(waitqueue_active(&ctx->fault_pending_wqh));
+		VM_WARN_ON_ONCE(spin_is_locked(&ctx->fault_wqh.lock));
+		VM_WARN_ON_ONCE(waitqueue_active(&ctx->fault_wqh));
+		VM_WARN_ON_ONCE(spin_is_locked(&ctx->event_wqh.lock));
+		VM_WARN_ON_ONCE(waitqueue_active(&ctx->event_wqh));
+		VM_WARN_ON_ONCE(spin_is_locked(&ctx->fd_wqh.lock));
+		VM_WARN_ON_ONCE(waitqueue_active(&ctx->fd_wqh));
+		mmdrop(ctx->mm);
+		kmem_cache_free(userfaultfd_ctx_cachep, ctx);
+	}
+}
+
+static inline void msg_init(struct uffd_msg *msg)
+{
+	BUILD_BUG_ON(sizeof(struct uffd_msg) != 32);
+	/*
+	 * Must use memset to zero out the paddings or kernel data is
+	 * leaked to userland.
+	 */
+	memset(msg, 0, sizeof(struct uffd_msg));
+}
+
+static inline struct uffd_msg userfault_msg(unsigned long address,
+					    unsigned long real_address,
+					    unsigned int flags,
+					    unsigned long reason,
+					    unsigned int features)
+{
+	struct uffd_msg msg;
+
+	msg_init(&msg);
+	msg.event = UFFD_EVENT_PAGEFAULT;
+
+	msg.arg.pagefault.address = (features & UFFD_FEATURE_EXACT_ADDRESS) ?
+				    real_address : address;
+
+	/*
+	 * These flags indicate why the userfault occurred:
+	 * - UFFD_PAGEFAULT_FLAG_WP indicates a write protect fault.
+	 * - UFFD_PAGEFAULT_FLAG_MINOR indicates a minor fault.
+	 * - Neither of these flags being set indicates a MISSING fault.
+	 *
+	 * Separately, UFFD_PAGEFAULT_FLAG_WRITE indicates it was a write
+	 * fault. Otherwise, it was a read fault.
+	 */
+	if (flags & FAULT_FLAG_WRITE)
+		msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WRITE;
+	if (reason & VM_UFFD_WP)
+		msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WP;
+	if (reason & VM_UFFD_MINOR)
+		msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_MINOR;
+	if (features & UFFD_FEATURE_THREAD_ID)
+		msg.arg.pagefault.feat.ptid = task_pid_vnr(current);
+	return msg;
+}
+
+#ifdef CONFIG_HUGETLB_PAGE
+/*
+ * Same functionality as userfaultfd_must_wait below with modifications for
+ * hugepmd ranges.
+ */
+static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
+					      struct vm_fault *vmf,
+					      unsigned long reason)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	pte_t *ptep, pte;
+
+	assert_fault_locked(vmf);
+
+	ptep = hugetlb_walk(vma, vmf->address, vma_mmu_pagesize(vma));
+	if (!ptep)
+		return true;
+
+	pte = huge_ptep_get(vma->vm_mm, vmf->address, ptep);
+
+	/*
+	 * Lockless access: we're in a wait_event so it's ok if it
+	 * changes under us.
+	 */
+
+	/* Entry is still missing, wait for userspace to resolve the fault. */
+	if (huge_pte_none(pte))
+		return true;
+	/* UFFD PTE markers require userspace to resolve the fault. */
+	if (pte_is_uffd_marker(pte))
+		return true;
+	/*
+	 * If VMA has UFFD WP faults enabled and WP fault, wait for userspace to
+	 * resolve the fault.
+	 */
+	if (!huge_pte_write(pte) && (reason & VM_UFFD_WP))
+		return true;
+
+	return false;
+}
+#else
+static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
+					      struct vm_fault *vmf,
+					      unsigned long reason)
+{
+	/* Should never get here. */
+	VM_WARN_ON_ONCE(1);
+	return false;
+}
+#endif /* CONFIG_HUGETLB_PAGE */
+
+/*
+ * Verify the pagetables are still not ok after having registered into
+ * the fault_pending_wqh to avoid userland having to UFFDIO_WAKE any
+ * userfault that has already been resolved, if userfaultfd_read_iter and
+ * UFFDIO_COPY|ZEROPAGE are being run simultaneously on two different
+ * threads.
+ */
+static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx,
+					 struct vm_fault *vmf,
+					 unsigned long reason)
+{
+	struct mm_struct *mm = ctx->mm;
+	unsigned long address = vmf->address;
+	pgd_t *pgd;
+	p4d_t *p4d;
+	pud_t *pud;
+	pmd_t *pmd, _pmd;
+	pte_t *pte;
+	pte_t ptent;
+	bool ret;
+
+	assert_fault_locked(vmf);
+
+	pgd = pgd_offset(mm, address);
+	if (!pgd_present(*pgd))
+		return true;
+	p4d = p4d_offset(pgd, address);
+	if (!p4d_present(*p4d))
+		return true;
+	pud = pud_offset(p4d, address);
+	if (!pud_present(*pud))
+		return true;
+	pmd = pmd_offset(pud, address);
+again:
+	_pmd = pmdp_get_lockless(pmd);
+	if (pmd_none(_pmd))
+		return true;
+
+	/*
+	 * A race could arise which would result in a softleaf entry such as
+	 * migration entry unexpectedly being present in the PMD, so explicitly
+	 * check for this and bail out if so.
+	 */
+	if (!pmd_present(_pmd))
+		return false;
+
+	if (pmd_trans_huge(_pmd))
+		return !pmd_write(_pmd) && (reason & VM_UFFD_WP);
+
+	pte = pte_offset_map(pmd, address);
+	if (!pte)
+		goto again;
+
+	/*
+	 * Lockless access: we're in a wait_event so it's ok if it
+	 * changes under us.
+	 */
+	ptent = ptep_get(pte);
+
+	ret = true;
+	/* Entry is still missing, wait for userspace to resolve the fault. */
+	if (pte_none(ptent))
+		goto out;
+	/* UFFD PTE markers require userspace to resolve the fault. */
+	if (pte_is_uffd_marker(ptent))
+		goto out;
+	/*
+	 * If VMA has UFFD WP faults enabled and WP fault, wait for userspace to
+	 * resolve the fault.
+	 */
+	if (!pte_write(ptent) && (reason & VM_UFFD_WP))
+		goto out;
+
+	ret = false;
+out:
+	pte_unmap(pte);
+	return ret;
+}
+
+static inline unsigned int userfaultfd_get_blocking_state(unsigned int flags)
+{
+	if (flags & FAULT_FLAG_INTERRUPTIBLE)
+		return TASK_INTERRUPTIBLE;
+
+	if (flags & FAULT_FLAG_KILLABLE)
+		return TASK_KILLABLE;
+
+	return TASK_UNINTERRUPTIBLE;
+}
+
+/*
+ * The locking rules involved in returning VM_FAULT_RETRY depending on
+ * FAULT_FLAG_ALLOW_RETRY, FAULT_FLAG_RETRY_NOWAIT and
+ * FAULT_FLAG_KILLABLE are not straightforward. The "Caution"
+ * recommendation in __lock_page_or_retry is not an understatement.
+ *
+ * If FAULT_FLAG_ALLOW_RETRY is set, the mmap_lock must be released
+ * before returning VM_FAULT_RETRY only if FAULT_FLAG_RETRY_NOWAIT is
+ * not set.
+ *
+ * If FAULT_FLAG_ALLOW_RETRY is set but FAULT_FLAG_KILLABLE is not
+ * set, VM_FAULT_RETRY can still be returned if and only if there are
+ * fatal_signal_pending()s, and the mmap_lock must be released before
+ * returning it.
+ */
+vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	struct mm_struct *mm = vma->vm_mm;
+	struct userfaultfd_ctx *ctx;
+	struct userfaultfd_wait_queue uwq;
+	vm_fault_t ret = VM_FAULT_SIGBUS;
+	bool must_wait;
+	unsigned int blocking_state;
+
+	/*
+	 * We don't do userfault handling for the final child pid update
+	 * and when coredumping (faults triggered by get_dump_page()).
+	 */
+	if (current->flags & (PF_EXITING|PF_DUMPCORE))
+		goto out;
+
+	assert_fault_locked(vmf);
+
+	ctx = vma->vm_userfaultfd_ctx.ctx;
+	if (!ctx)
+		goto out;
+
+	VM_WARN_ON_ONCE(ctx->mm != mm);
+
+	/* Any unrecognized flag is a bug. */
+	VM_WARN_ON_ONCE(reason & ~__VM_UFFD_FLAGS);
+	/* 0 or > 1 flags set is a bug; we expect exactly 1. */
+	VM_WARN_ON_ONCE(!reason || (reason & (reason - 1)));
+
+	if (ctx->features & UFFD_FEATURE_SIGBUS)
+		goto out;
+	if (!(vmf->flags & FAULT_FLAG_USER) && (ctx->flags & UFFD_USER_MODE_ONLY))
+		goto out;
+
+	/*
+	 * Check that we can return VM_FAULT_RETRY.
+	 *
+	 * NOTE: it should become possible to return VM_FAULT_RETRY
+	 * even if FAULT_FLAG_TRIED is set without leading to gup()
+	 * -EBUSY failures, if the userfaultfd is to be extended for
+	 * VM_UFFD_WP tracking and we intend to arm the userfault
+	 * without first stopping userland access to the memory. For
+	 * VM_UFFD_MISSING userfaults this is enough for now.
+	 */
+	if (unlikely(!(vmf->flags & FAULT_FLAG_ALLOW_RETRY))) {
+		/*
+		 * Validate the invariant that nowait must allow retry
+		 * to be sure not to return SIGBUS erroneously on
+		 * nowait invocations.
+		 */
+		VM_WARN_ON_ONCE(vmf->flags & FAULT_FLAG_RETRY_NOWAIT);
+#ifdef CONFIG_DEBUG_VM
+		if (printk_ratelimit()) {
+			pr_warn("FAULT_FLAG_ALLOW_RETRY missing %x\n",
+				vmf->flags);
+			dump_stack();
+		}
+#endif
+		goto out;
+	}
+
+	/*
+	 * Handle nowait, not much to do other than tell it to retry
+	 * and wait.
+	 */
+	ret = VM_FAULT_RETRY;
+	if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
+		goto out;
+
+	if (unlikely(READ_ONCE(ctx->released))) {
+		/*
+		 * If a concurrent release is detected, do not return
+		 * VM_FAULT_SIGBUS or VM_FAULT_NOPAGE, but instead always
+		 * return VM_FAULT_RETRY with lock released proactively.
+		 *
+		 * If we were to return VM_FAULT_SIGBUS here, the non
+		 * cooperative manager would be instead forced to
+		 * always call UFFDIO_UNREGISTER before it can safely
+		 * close the uffd, to avoid involuntary SIGBUS triggered.
+		 *
+		 * If we were to return VM_FAULT_NOPAGE, it would work for
+		 * the fault path, in which the lock will be released
+		 * later.  However for GUP, faultin_page() does nothing
+		 * special on NOPAGE, so GUP would spin retrying without
+		 * releasing the mmap read lock, causing possible livelock.
+		 *
+		 * Here only VM_FAULT_RETRY would make sure the mmap lock
+		 * be released immediately, so that the thread concurrently
+		 * releasing the userfault would always make progress.
+		 */
+		release_fault_lock(vmf);
+		goto out;
+	}
+
+	/* take the reference before dropping the mmap_lock */
+	userfaultfd_ctx_get(ctx);
+
+	init_waitqueue_func_entry(&uwq.wq, userfaultfd_wake_function);
+	uwq.wq.private = current;
+	uwq.msg = userfault_msg(vmf->address, vmf->real_address, vmf->flags,
+				reason, ctx->features);
+	uwq.ctx = ctx;
+	uwq.waken = false;
+
+	blocking_state = userfaultfd_get_blocking_state(vmf->flags);
+
+	/*
+	 * Take the vma lock now, in order to safely call
+	 * userfaultfd_huge_must_wait() later. Since acquiring the
+	 * (sleepable) vma lock can modify the current task state, that
+	 * must be before explicitly calling set_current_state().
+	 */
+	if (is_vm_hugetlb_page(vma))
+		hugetlb_vma_lock_read(vma);
+
+	spin_lock_irq(&ctx->fault_pending_wqh.lock);
+	/*
+	 * After the __add_wait_queue the uwq is visible to userland
+	 * through poll/read().
+	 */
+	__add_wait_queue(&ctx->fault_pending_wqh, &uwq.wq);
+	/*
+	 * The smp_mb() after __set_current_state prevents the reads
+	 * following the spin_unlock to happen before the list_add in
+	 * __add_wait_queue.
+	 */
+	set_current_state(blocking_state);
+	spin_unlock_irq(&ctx->fault_pending_wqh.lock);
+
+	if (is_vm_hugetlb_page(vma)) {
+		must_wait = userfaultfd_huge_must_wait(ctx, vmf, reason);
+		hugetlb_vma_unlock_read(vma);
+	} else {
+		must_wait = userfaultfd_must_wait(ctx, vmf, reason);
+	}
+
+	release_fault_lock(vmf);
+
+	if (likely(must_wait && !READ_ONCE(ctx->released))) {
+		wake_up_poll(&ctx->fd_wqh, EPOLLIN);
+		schedule();
+	}
+
+	__set_current_state(TASK_RUNNING);
+
+	/*
+	 * Here we race with the list_del; list_add in
+	 * userfaultfd_ctx_read(), however because we don't ever run
+	 * list_del_init() to refile across the two lists, the prev
+	 * and next pointers will never point to self. list_add also
+	 * would never let any of the two pointers to point to
+	 * self. So list_empty_careful won't risk to see both pointers
+	 * pointing to self at any time during the list refile. The
+	 * only case where list_del_init() is called is the full
+	 * removal in the wake function and there we don't re-list_add
+	 * and it's fine not to block on the spinlock. The uwq on this
+	 * kernel stack can be released after the list_del_init.
+	 */
+	if (!list_empty_careful(&uwq.wq.entry)) {
+		spin_lock_irq(&ctx->fault_pending_wqh.lock);
+		/*
+		 * No need of list_del_init(), the uwq on the stack
+		 * will be freed shortly anyway.
+		 */
+		list_del(&uwq.wq.entry);
+		spin_unlock_irq(&ctx->fault_pending_wqh.lock);
+	}
+
+	/*
+	 * ctx may go away after this if the userfault pseudo fd is
+	 * already released.
+	 */
+	userfaultfd_ctx_put(ctx);
+
+out:
+	return ret;
+}
+
+static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
+					      struct userfaultfd_wait_queue *ewq)
+{
+	struct userfaultfd_ctx *release_new_ctx;
+
+	if (WARN_ON_ONCE(current->flags & PF_EXITING))
+		goto out;
+
+	ewq->ctx = ctx;
+	init_waitqueue_entry(&ewq->wq, current);
+	release_new_ctx = NULL;
+
+	spin_lock_irq(&ctx->event_wqh.lock);
+	/*
+	 * After the __add_wait_queue the uwq is visible to userland
+	 * through poll/read().
+	 */
+	__add_wait_queue(&ctx->event_wqh, &ewq->wq);
+	for (;;) {
+		set_current_state(TASK_KILLABLE);
+		if (ewq->msg.event == 0)
+			break;
+		if (READ_ONCE(ctx->released) ||
+		    fatal_signal_pending(current)) {
+			/*
+			 * &ewq->wq may be queued in fork_event, but
+			 * __remove_wait_queue ignores the head
+			 * parameter. It would be a problem if it
+			 * didn't.
+			 */
+			__remove_wait_queue(&ctx->event_wqh, &ewq->wq);
+			if (ewq->msg.event == UFFD_EVENT_FORK) {
+				struct userfaultfd_ctx *new;
+
+				new = (struct userfaultfd_ctx *)
+					(unsigned long)
+					ewq->msg.arg.reserved.reserved1;
+				release_new_ctx = new;
+			}
+			break;
+		}
+
+		spin_unlock_irq(&ctx->event_wqh.lock);
+
+		wake_up_poll(&ctx->fd_wqh, EPOLLIN);
+		schedule();
+
+		spin_lock_irq(&ctx->event_wqh.lock);
+	}
+	__set_current_state(TASK_RUNNING);
+	spin_unlock_irq(&ctx->event_wqh.lock);
+
+	if (release_new_ctx) {
+		userfaultfd_release_new(release_new_ctx);
+		userfaultfd_ctx_put(release_new_ctx);
+	}
+
+	/*
+	 * ctx may go away after this if the userfault pseudo fd is
+	 * already released.
+	 */
+out:
+	atomic_dec(&ctx->mmap_changing);
+	VM_WARN_ON_ONCE(atomic_read(&ctx->mmap_changing) < 0);
+	userfaultfd_ctx_put(ctx);
+}
+
+static void userfaultfd_event_complete(struct userfaultfd_ctx *ctx,
+				       struct userfaultfd_wait_queue *ewq)
+{
+	ewq->msg.event = 0;
+	wake_up_locked(&ctx->event_wqh);
+	__remove_wait_queue(&ctx->event_wqh, &ewq->wq);
+}
+
+int dup_userfaultfd(struct vm_area_struct *vma, struct list_head *fcs)
+{
+	struct userfaultfd_ctx *ctx = NULL, *octx;
+	struct userfaultfd_fork_ctx *fctx;
+
+	octx = vma->vm_userfaultfd_ctx.ctx;
+	if (!octx)
+		return 0;
+
+	if (!(octx->features & UFFD_FEATURE_EVENT_FORK)) {
+		userfaultfd_reset_ctx(vma);
+		return 0;
+	}
+
+	list_for_each_entry(fctx, fcs, list)
+		if (fctx->orig == octx) {
+			ctx = fctx->new;
+			break;
+		}
+
+	if (!ctx) {
+		fctx = kmalloc_obj(*fctx);
+		if (!fctx)
+			return -ENOMEM;
+
+		ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
+		if (!ctx) {
+			kfree(fctx);
+			return -ENOMEM;
+		}
+
+		refcount_set(&ctx->refcount, 1);
+		ctx->flags = octx->flags;
+		ctx->features = octx->features;
+		ctx->released = false;
+		init_rwsem(&ctx->map_changing_lock);
+		atomic_set(&ctx->mmap_changing, 0);
+		ctx->mm = vma->vm_mm;
+		mmgrab(ctx->mm);
+
+		userfaultfd_ctx_get(octx);
+		down_write(&octx->map_changing_lock);
+		atomic_inc(&octx->mmap_changing);
+		up_write(&octx->map_changing_lock);
+		fctx->orig = octx;
+		fctx->new = ctx;
+		list_add_tail(&fctx->list, fcs);
+	}
+
+	vma->vm_userfaultfd_ctx.ctx = ctx;
+	return 0;
+}
+
+static void dup_fctx(struct userfaultfd_fork_ctx *fctx)
+{
+	struct userfaultfd_ctx *ctx = fctx->orig;
+	struct userfaultfd_wait_queue ewq;
+
+	msg_init(&ewq.msg);
+
+	ewq.msg.event = UFFD_EVENT_FORK;
+	ewq.msg.arg.reserved.reserved1 = (unsigned long)fctx->new;
+
+	userfaultfd_event_wait_completion(ctx, &ewq);
+}
+
+void dup_userfaultfd_complete(struct list_head *fcs)
+{
+	struct userfaultfd_fork_ctx *fctx, *n;
+
+	list_for_each_entry_safe(fctx, n, fcs, list) {
+		dup_fctx(fctx);
+		list_del(&fctx->list);
+		kfree(fctx);
+	}
+}
+
+void dup_userfaultfd_fail(struct list_head *fcs)
+{
+	struct userfaultfd_fork_ctx *fctx, *n;
+
+	/*
+	 * An error has occurred on fork, we will tear memory down, but have
+	 * allocated memory for fctx's and raised reference counts for both the
+	 * original and child contexts (and on the mm for each as a result).
+	 *
+	 * These would ordinarily be taken care of by a user handling the event,
+	 * but we are no longer doing so, so manually clean up here.
+	 *
+	 * mm tear down will take care of cleaning up VMA contexts.
+	 */
+	list_for_each_entry_safe(fctx, n, fcs, list) {
+		struct userfaultfd_ctx *octx = fctx->orig;
+		struct userfaultfd_ctx *ctx = fctx->new;
+
+		atomic_dec(&octx->mmap_changing);
+		VM_WARN_ON_ONCE(atomic_read(&octx->mmap_changing) < 0);
+		userfaultfd_ctx_put(octx);
+		userfaultfd_ctx_put(ctx);
+
+		list_del(&fctx->list);
+		kfree(fctx);
+	}
+}
+
+void mremap_userfaultfd_prep(struct vm_area_struct *vma,
+			     struct vm_userfaultfd_ctx *vm_ctx)
+{
+	struct userfaultfd_ctx *ctx;
+
+	ctx = vma->vm_userfaultfd_ctx.ctx;
+
+	if (!ctx)
+		return;
+
+	if (ctx->features & UFFD_FEATURE_EVENT_REMAP) {
+		vm_ctx->ctx = ctx;
+		userfaultfd_ctx_get(ctx);
+		down_write(&ctx->map_changing_lock);
+		atomic_inc(&ctx->mmap_changing);
+		up_write(&ctx->map_changing_lock);
+	} else {
+		/* Drop uffd context if remap feature not enabled */
+		userfaultfd_reset_ctx(vma);
+	}
+}
+
+void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx *vm_ctx,
+				 unsigned long from, unsigned long to,
+				 unsigned long len)
+{
+	struct userfaultfd_ctx *ctx = vm_ctx->ctx;
+	struct userfaultfd_wait_queue ewq;
+
+	if (!ctx)
+		return;
+
+	msg_init(&ewq.msg);
+
+	ewq.msg.event = UFFD_EVENT_REMAP;
+	ewq.msg.arg.remap.from = from;
+	ewq.msg.arg.remap.to = to;
+	ewq.msg.arg.remap.len = len;
+
+	userfaultfd_event_wait_completion(ctx, &ewq);
+}
+
+void mremap_userfaultfd_fail(struct vm_userfaultfd_ctx *vm_ctx)
+{
+	struct userfaultfd_ctx *ctx = vm_ctx->ctx;
+
+	if (!ctx)
+		return;
+
+	userfaultfd_ctx_put(ctx);
+}
+
+bool userfaultfd_remove(struct vm_area_struct *vma,
+			unsigned long start, unsigned long end)
+{
+	struct mm_struct *mm = vma->vm_mm;
+	struct userfaultfd_ctx *ctx;
+	struct userfaultfd_wait_queue ewq;
+
+	ctx = vma->vm_userfaultfd_ctx.ctx;
+	if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_REMOVE))
+		return true;
+
+	userfaultfd_ctx_get(ctx);
+	down_write(&ctx->map_changing_lock);
+	atomic_inc(&ctx->mmap_changing);
+	up_write(&ctx->map_changing_lock);
+	mmap_read_unlock(mm);
+
+	msg_init(&ewq.msg);
+
+	ewq.msg.event = UFFD_EVENT_REMOVE;
+	ewq.msg.arg.remove.start = start;
+	ewq.msg.arg.remove.end = end;
+
+	userfaultfd_event_wait_completion(ctx, &ewq);
+
+	return false;
+}
+
+static bool has_unmap_ctx(struct userfaultfd_ctx *ctx, struct list_head *unmaps,
+			  unsigned long start, unsigned long end)
+{
+	struct userfaultfd_unmap_ctx *unmap_ctx;
+
+	list_for_each_entry(unmap_ctx, unmaps, list)
+		if (unmap_ctx->ctx == ctx && unmap_ctx->start == start &&
+		    unmap_ctx->end == end)
+			return true;
+
+	return false;
+}
+
+int userfaultfd_unmap_prep(struct vm_area_struct *vma, unsigned long start,
+			   unsigned long end, struct list_head *unmaps)
+{
+	struct userfaultfd_unmap_ctx *unmap_ctx;
+	struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx;
+
+	if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_UNMAP) ||
+	    has_unmap_ctx(ctx, unmaps, start, end))
+		return 0;
+
+	unmap_ctx = kzalloc_obj(*unmap_ctx);
+	if (!unmap_ctx)
+		return -ENOMEM;
+
+	userfaultfd_ctx_get(ctx);
+	down_write(&ctx->map_changing_lock);
+	atomic_inc(&ctx->mmap_changing);
+	up_write(&ctx->map_changing_lock);
+	unmap_ctx->ctx = ctx;
+	unmap_ctx->start = start;
+	unmap_ctx->end = end;
+	list_add_tail(&unmap_ctx->list, unmaps);
+
+	return 0;
+}
+
+void userfaultfd_unmap_complete(struct mm_struct *mm, struct list_head *uf)
+{
+	struct userfaultfd_unmap_ctx *ctx, *n;
+	struct userfaultfd_wait_queue ewq;
+
+	list_for_each_entry_safe(ctx, n, uf, list) {
+		msg_init(&ewq.msg);
+
+		ewq.msg.event = UFFD_EVENT_UNMAP;
+		ewq.msg.arg.remove.start = ctx->start;
+		ewq.msg.arg.remove.end = ctx->end;
+
+		userfaultfd_event_wait_completion(ctx->ctx, &ewq);
+
+		list_del(&ctx->list);
+		kfree(ctx);
+	}
+}
+
+static int userfaultfd_release(struct inode *inode, struct file *file)
+{
+	struct userfaultfd_ctx *ctx = file->private_data;
+	struct mm_struct *mm = ctx->mm;
+	/* len == 0 means wake all */
+	struct userfaultfd_wake_range range = { .len = 0, };
+
+	WRITE_ONCE(ctx->released, true);
+
+	userfaultfd_release_all(mm, ctx);
+
+	/*
+	 * After no new page faults can wait on this fault_*wqh, flush
+	 * the last page faults that may have been already waiting on
+	 * the fault_*wqh.
+	 */
+	spin_lock_irq(&ctx->fault_pending_wqh.lock);
+	__wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, &range);
+	__wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, &range);
+	spin_unlock_irq(&ctx->fault_pending_wqh.lock);
+
+	/* Flush pending events that may still wait on event_wqh */
+	wake_up_all(&ctx->event_wqh);
+
+	wake_up_poll(&ctx->fd_wqh, EPOLLHUP);
+	userfaultfd_ctx_put(ctx);
+	return 0;
+}
+
+/* fault_pending_wqh.lock must be hold by the caller */
+static inline struct userfaultfd_wait_queue *find_userfault_in(
+		wait_queue_head_t *wqh)
+{
+	wait_queue_entry_t *wq;
+	struct userfaultfd_wait_queue *uwq;
+
+	lockdep_assert_held(&wqh->lock);
+
+	uwq = NULL;
+	if (!waitqueue_active(wqh))
+		goto out;
+	/* walk in reverse to provide FIFO behavior to read userfaults */
+	wq = list_last_entry(&wqh->head, typeof(*wq), entry);
+	uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
+out:
+	return uwq;
+}
+
+static inline struct userfaultfd_wait_queue *find_userfault(
+		struct userfaultfd_ctx *ctx)
+{
+	return find_userfault_in(&ctx->fault_pending_wqh);
+}
+
+static inline struct userfaultfd_wait_queue *find_userfault_evt(
+		struct userfaultfd_ctx *ctx)
+{
+	return find_userfault_in(&ctx->event_wqh);
+}
+
+static __poll_t userfaultfd_poll(struct file *file, poll_table *wait)
+{
+	struct userfaultfd_ctx *ctx = file->private_data;
+	__poll_t ret;
+
+	poll_wait(file, &ctx->fd_wqh, wait);
+
+	if (!userfaultfd_is_initialized(ctx))
+		return EPOLLERR;
+
+	/*
+	 * poll() never guarantees that read won't block.
+	 * userfaults can be waken before they're read().
+	 */
+	if (unlikely(!(file->f_flags & O_NONBLOCK)))
+		return EPOLLERR;
+	/*
+	 * lockless access to see if there are pending faults
+	 * __pollwait last action is the add_wait_queue but
+	 * the spin_unlock would allow the waitqueue_active to
+	 * pass above the actual list_add inside
+	 * add_wait_queue critical section. So use a full
+	 * memory barrier to serialize the list_add write of
+	 * add_wait_queue() with the waitqueue_active read
+	 * below.
+	 */
+	ret = 0;
+	smp_mb();
+	if (waitqueue_active(&ctx->fault_pending_wqh))
+		ret = EPOLLIN;
+	else if (waitqueue_active(&ctx->event_wqh))
+		ret = EPOLLIN;
+
+	return ret;
+}
+
+static const struct file_operations userfaultfd_fops;
+
+static int resolve_userfault_fork(struct userfaultfd_ctx *new,
+				  struct inode *inode,
+				  struct uffd_msg *msg)
+{
+	int fd;
+
+	fd = anon_inode_create_getfd("[userfaultfd]", &userfaultfd_fops, new,
+			O_RDONLY | (new->flags & UFFD_SHARED_FCNTL_FLAGS), inode);
+	if (fd < 0)
+		return fd;
+
+	msg->arg.reserved.reserved1 = 0;
+	msg->arg.fork.ufd = fd;
+	return 0;
+}
+
+static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
+				    struct uffd_msg *msg, struct inode *inode)
+{
+	ssize_t ret;
+	DECLARE_WAITQUEUE(wait, current);
+	struct userfaultfd_wait_queue *uwq;
+	/*
+	 * Handling fork event requires sleeping operations, so
+	 * we drop the event_wqh lock, then do these ops, then
+	 * lock it back and wake up the waiter. While the lock is
+	 * dropped the ewq may go away so we keep track of it
+	 * carefully.
+	 */
+	LIST_HEAD(fork_event);
+	struct userfaultfd_ctx *fork_nctx = NULL;
+
+	/* always take the fd_wqh lock before the fault_pending_wqh lock */
+	spin_lock_irq(&ctx->fd_wqh.lock);
+	__add_wait_queue(&ctx->fd_wqh, &wait);
+	for (;;) {
+		set_current_state(TASK_INTERRUPTIBLE);
+		spin_lock(&ctx->fault_pending_wqh.lock);
+		uwq = find_userfault(ctx);
+		if (uwq) {
+			/*
+			 * Use a seqcount to repeat the lockless check
+			 * in wake_userfault() to avoid missing
+			 * wakeups because during the refile both
+			 * waitqueue could become empty if this is the
+			 * only userfault.
+			 */
+			write_seqcount_begin(&ctx->refile_seq);
+
+			/*
+			 * The fault_pending_wqh.lock prevents the uwq
+			 * to disappear from under us.
+			 *
+			 * Refile this userfault from
+			 * fault_pending_wqh to fault_wqh, it's not
+			 * pending anymore after we read it.
+			 *
+			 * Use list_del() by hand (as
+			 * userfaultfd_wake_function also uses
+			 * list_del_init() by hand) to be sure nobody
+			 * changes __remove_wait_queue() to use
+			 * list_del_init() in turn breaking the
+			 * !list_empty_careful() check in
+			 * handle_userfault(). The uwq->wq.head list
+			 * must never be empty at any time during the
+			 * refile, or the waitqueue could disappear
+			 * from under us. The "wait_queue_head_t"
+			 * parameter of __remove_wait_queue() is unused
+			 * anyway.
+			 */
+			list_del(&uwq->wq.entry);
+			add_wait_queue(&ctx->fault_wqh, &uwq->wq);
+
+			write_seqcount_end(&ctx->refile_seq);
+
+			/* careful to always initialize msg if ret == 0 */
+			*msg = uwq->msg;
+			spin_unlock(&ctx->fault_pending_wqh.lock);
+			ret = 0;
+			break;
+		}
+		spin_unlock(&ctx->fault_pending_wqh.lock);
+
+		spin_lock(&ctx->event_wqh.lock);
+		uwq = find_userfault_evt(ctx);
+		if (uwq) {
+			*msg = uwq->msg;
+
+			if (uwq->msg.event == UFFD_EVENT_FORK) {
+				fork_nctx = (struct userfaultfd_ctx *)
+					(unsigned long)
+					uwq->msg.arg.reserved.reserved1;
+				list_move(&uwq->wq.entry, &fork_event);
+				/*
+				 * fork_nctx can be freed as soon as
+				 * we drop the lock, unless we take a
+				 * reference on it.
+				 */
+				userfaultfd_ctx_get(fork_nctx);
+				spin_unlock(&ctx->event_wqh.lock);
+				ret = 0;
+				break;
+			}
+
+			userfaultfd_event_complete(ctx, uwq);
+			spin_unlock(&ctx->event_wqh.lock);
+			ret = 0;
+			break;
+		}
+		spin_unlock(&ctx->event_wqh.lock);
+
+		if (signal_pending(current)) {
+			ret = -ERESTARTSYS;
+			break;
+		}
+		if (no_wait) {
+			ret = -EAGAIN;
+			break;
+		}
+		spin_unlock_irq(&ctx->fd_wqh.lock);
+		schedule();
+		spin_lock_irq(&ctx->fd_wqh.lock);
+	}
+	__remove_wait_queue(&ctx->fd_wqh, &wait);
+	__set_current_state(TASK_RUNNING);
+	spin_unlock_irq(&ctx->fd_wqh.lock);
+
+	if (!ret && msg->event == UFFD_EVENT_FORK) {
+		ret = resolve_userfault_fork(fork_nctx, inode, msg);
+		spin_lock_irq(&ctx->event_wqh.lock);
+		if (!list_empty(&fork_event)) {
+			/*
+			 * The fork thread didn't abort, so we can
+			 * drop the temporary refcount.
+			 */
+			userfaultfd_ctx_put(fork_nctx);
+
+			uwq = list_first_entry(&fork_event,
+					       typeof(*uwq),
+					       wq.entry);
+			/*
+			 * If fork_event list wasn't empty and in turn
+			 * the event wasn't already released by fork
+			 * (the event is allocated on fork kernel
+			 * stack), put the event back to its place in
+			 * the event_wq. fork_event head will be freed
+			 * as soon as we return so the event cannot
+			 * stay queued there no matter the current
+			 * "ret" value.
+			 */
+			list_del(&uwq->wq.entry);
+			__add_wait_queue(&ctx->event_wqh, &uwq->wq);
+
+			/*
+			 * Leave the event in the waitqueue and report
+			 * error to userland if we failed to resolve
+			 * the userfault fork.
+			 */
+			if (likely(!ret))
+				userfaultfd_event_complete(ctx, uwq);
+		} else {
+			/*
+			 * Here the fork thread aborted and the
+			 * refcount from the fork thread on fork_nctx
+			 * has already been released. We still hold
+			 * the reference we took before releasing the
+			 * lock above. If resolve_userfault_fork
+			 * failed we've to drop it because the
+			 * fork_nctx has to be freed in such case. If
+			 * it succeeded we'll hold it because the new
+			 * uffd references it.
+			 */
+			if (ret)
+				userfaultfd_ctx_put(fork_nctx);
+		}
+		spin_unlock_irq(&ctx->event_wqh.lock);
+	}
+
+	return ret;
+}
+
+static ssize_t userfaultfd_read_iter(struct kiocb *iocb, struct iov_iter *to)
+{
+	struct file *file = iocb->ki_filp;
+	struct userfaultfd_ctx *ctx = file->private_data;
+	ssize_t _ret, ret = 0;
+	struct uffd_msg msg;
+	struct inode *inode = file_inode(file);
+	bool no_wait;
+
+	if (!userfaultfd_is_initialized(ctx))
+		return -EINVAL;
+
+	no_wait = file->f_flags & O_NONBLOCK || iocb->ki_flags & IOCB_NOWAIT;
+	for (;;) {
+		if (iov_iter_count(to) < sizeof(msg))
+			return ret ? ret : -EINVAL;
+		_ret = userfaultfd_ctx_read(ctx, no_wait, &msg, inode);
+		if (_ret < 0)
+			return ret ? ret : _ret;
+		_ret = !copy_to_iter_full(&msg, sizeof(msg), to);
+		if (_ret)
+			return ret ? ret : -EFAULT;
+		ret += sizeof(msg);
+		/*
+		 * Allow to read more than one fault at time but only
+		 * block if waiting for the very first one.
+		 */
+		no_wait = true;
+	}
+}
+
+static void __wake_userfault(struct userfaultfd_ctx *ctx,
+			     struct userfaultfd_wake_range *range)
+{
+	spin_lock_irq(&ctx->fault_pending_wqh.lock);
+	/* wake all in the range and autoremove */
+	if (waitqueue_active(&ctx->fault_pending_wqh))
+		__wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL,
+				     range);
+	if (waitqueue_active(&ctx->fault_wqh))
+		__wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, range);
+	spin_unlock_irq(&ctx->fault_pending_wqh.lock);
+}
+
+static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx,
+					   struct userfaultfd_wake_range *range)
+{
+	unsigned seq;
+	bool need_wakeup;
+
+	/*
+	 * To be sure waitqueue_active() is not reordered by the CPU
+	 * before the pagetable update, use an explicit SMP memory
+	 * barrier here. PT lock release or mmap_read_unlock(mm) still
+	 * have release semantics that can allow the
+	 * waitqueue_active() to be reordered before the pte update.
+	 */
+	smp_mb();
+
+	/*
+	 * Use waitqueue_active because it's very frequent to
+	 * change the address space atomically even if there are no
+	 * userfaults yet. So we take the spinlock only when we're
+	 * sure we've userfaults to wake.
+	 */
+	do {
+		seq = read_seqcount_begin(&ctx->refile_seq);
+		need_wakeup = waitqueue_active(&ctx->fault_pending_wqh) ||
+			waitqueue_active(&ctx->fault_wqh);
+		cond_resched();
+	} while (read_seqcount_retry(&ctx->refile_seq, seq));
+	if (need_wakeup)
+		__wake_userfault(ctx, range);
+}
+
+static __always_inline int validate_unaligned_range(
+	struct mm_struct *mm, __u64 start, __u64 len)
+{
+	__u64 task_size = mm->task_size;
+
+	if (len & ~PAGE_MASK)
+		return -EINVAL;
+	if (!len)
+		return -EINVAL;
+	if (start >= task_size)
+		return -EINVAL;
+	if (len > task_size - start)
+		return -EINVAL;
+	if (start + len <= start)
+		return -EINVAL;
+	return 0;
+}
+
+static __always_inline int validate_range(struct mm_struct *mm,
+					  __u64 start, __u64 len)
+{
+	if (start & ~PAGE_MASK)
+		return -EINVAL;
+
+	return validate_unaligned_range(mm, start, len);
+}
+
+static int userfaultfd_register(struct userfaultfd_ctx *ctx,
+				unsigned long arg)
+{
+	struct mm_struct *mm = ctx->mm;
+	struct vm_area_struct *vma, *cur;
+	int ret;
+	struct uffdio_register uffdio_register;
+	struct uffdio_register __user *user_uffdio_register;
+	vm_flags_t vm_flags;
+	bool found;
+	bool basic_ioctls;
+	unsigned long start, end;
+	struct vma_iterator vmi;
+	bool wp_async = userfaultfd_wp_async_ctx(ctx);
+
+	user_uffdio_register = (struct uffdio_register __user *) arg;
+
+	ret = -EFAULT;
+	if (copy_from_user(&uffdio_register, user_uffdio_register,
+			   sizeof(uffdio_register)-sizeof(__u64)))
+		goto out;
+
+	ret = -EINVAL;
+	if (!uffdio_register.mode)
+		goto out;
+	if (uffdio_register.mode & ~UFFD_API_REGISTER_MODES)
+		goto out;
+	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 (!pgtable_supports_uffd_wp())
+			goto out;
+
+		vm_flags |= VM_UFFD_WP;
+	}
+	if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR) {
+#ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
+		goto out;
+#endif
+		vm_flags |= VM_UFFD_MINOR;
+	}
+
+	ret = validate_range(mm, uffdio_register.range.start,
+			     uffdio_register.range.len);
+	if (ret)
+		goto out;
+
+	start = uffdio_register.range.start;
+	end = start + uffdio_register.range.len;
+
+	ret = -ENOMEM;
+	if (!mmget_not_zero(mm))
+		goto out;
+
+	ret = -EINVAL;
+	mmap_write_lock(mm);
+	vma_iter_init(&vmi, mm, start);
+	vma = vma_find(&vmi, end);
+	if (!vma)
+		goto out_unlock;
+
+	/*
+	 * If the first vma contains huge pages, make sure start address
+	 * is aligned to huge page size.
+	 */
+	if (is_vm_hugetlb_page(vma)) {
+		unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
+
+		if (start & (vma_hpagesize - 1))
+			goto out_unlock;
+	}
+
+	/*
+	 * Search for not compatible vmas.
+	 */
+	found = false;
+	basic_ioctls = false;
+	cur = vma;
+	do {
+		cond_resched();
+
+		VM_WARN_ON_ONCE(!!cur->vm_userfaultfd_ctx.ctx ^
+				!!(cur->vm_flags & __VM_UFFD_FLAGS));
+
+		/* check not compatible vmas */
+		ret = -EINVAL;
+		if (!vma_can_userfault(cur, vm_flags, wp_async))
+			goto out_unlock;
+
+		/*
+		 * UFFDIO_COPY will fill file holes even without
+		 * PROT_WRITE. This check enforces that if this is a
+		 * MAP_SHARED, the process has write permission to the backing
+		 * file. If VM_MAYWRITE is set it also enforces that on a
+		 * MAP_SHARED vma: there is no F_WRITE_SEAL and no further
+		 * F_WRITE_SEAL can be taken until the vma is destroyed.
+		 */
+		ret = -EPERM;
+		if (unlikely(!(cur->vm_flags & VM_MAYWRITE)))
+			goto out_unlock;
+
+		/*
+		 * If this vma contains ending address, and huge pages
+		 * check alignment.
+		 */
+		if (is_vm_hugetlb_page(cur) && end <= cur->vm_end &&
+		    end > cur->vm_start) {
+			unsigned long vma_hpagesize = vma_kernel_pagesize(cur);
+
+			ret = -EINVAL;
+
+			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
+		 * different userfaultfd. We can't allow more than one
+		 * userfaultfd to own a single vma simultaneously or we
+		 * wouldn't know which one to deliver the userfaults to.
+		 */
+		ret = -EBUSY;
+		if (cur->vm_userfaultfd_ctx.ctx &&
+		    cur->vm_userfaultfd_ctx.ctx != ctx)
+			goto out_unlock;
+
+		/*
+		 * Note vmas containing huge pages
+		 */
+		if (is_vm_hugetlb_page(cur))
+			basic_ioctls = true;
+
+		found = true;
+	} for_each_vma_range(vmi, cur, end);
+	VM_WARN_ON_ONCE(!found);
+
+	ret = userfaultfd_register_range(ctx, vma, vm_flags, start, end,
+					 wp_async);
+
+out_unlock:
+	mmap_write_unlock(mm);
+	mmput(mm);
+	if (!ret) {
+		__u64 ioctls_out;
+
+		ioctls_out = basic_ioctls ? UFFD_API_RANGE_IOCTLS_BASIC :
+			UFFD_API_RANGE_IOCTLS;
+
+		/*
+		 * Declare the WP ioctl only if the WP mode is
+		 * specified and all checks passed with the range
+		 */
+		if (!(uffdio_register.mode & UFFDIO_REGISTER_MODE_WP))
+			ioctls_out &= ~((__u64)1 << _UFFDIO_WRITEPROTECT);
+
+		/* CONTINUE ioctl is only supported for MINOR ranges. */
+		if (!(uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR))
+			ioctls_out &= ~((__u64)1 << _UFFDIO_CONTINUE);
+
+		/*
+		 * Now that we scanned all vmas we can already tell
+		 * userland which ioctls methods are guaranteed to
+		 * succeed on this range.
+		 */
+		if (put_user(ioctls_out, &user_uffdio_register->ioctls))
+			ret = -EFAULT;
+	}
+out:
+	return ret;
+}
+
+static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
+				  unsigned long arg)
+{
+	struct mm_struct *mm = ctx->mm;
+	struct vm_area_struct *vma, *prev, *cur;
+	int ret;
+	struct uffdio_range uffdio_unregister;
+	bool found;
+	unsigned long start, end, vma_end;
+	const void __user *buf = (void __user *)arg;
+	struct vma_iterator vmi;
+	bool wp_async = userfaultfd_wp_async_ctx(ctx);
+
+	ret = -EFAULT;
+	if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister)))
+		goto out;
+
+	ret = validate_range(mm, uffdio_unregister.start,
+			     uffdio_unregister.len);
+	if (ret)
+		goto out;
+
+	start = uffdio_unregister.start;
+	end = start + uffdio_unregister.len;
+
+	ret = -ENOMEM;
+	if (!mmget_not_zero(mm))
+		goto out;
+
+	mmap_write_lock(mm);
+	ret = -EINVAL;
+	vma_iter_init(&vmi, mm, start);
+	vma = vma_find(&vmi, end);
+	if (!vma)
+		goto out_unlock;
+
+	/*
+	 * If the first vma contains huge pages, make sure start address
+	 * is aligned to huge page size.
+	 */
+	if (is_vm_hugetlb_page(vma)) {
+		unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
+
+		if (start & (vma_hpagesize - 1))
+			goto out_unlock;
+	}
+
+	/*
+	 * Search for not compatible vmas.
+	 */
+	found = false;
+	cur = vma;
+	do {
+		cond_resched();
+
+		VM_WARN_ON_ONCE(!!cur->vm_userfaultfd_ctx.ctx ^
+				!!(cur->vm_flags & __VM_UFFD_FLAGS));
+
+		/*
+		 * Prevent unregistering through a different userfaultfd than
+		 * the one used for registration.
+		 */
+		if (cur->vm_userfaultfd_ctx.ctx &&
+		    cur->vm_userfaultfd_ctx.ctx != ctx)
+			goto out_unlock;
+
+		/*
+		 * Check not compatible vmas, not strictly required
+		 * here as not compatible vmas cannot have an
+		 * userfaultfd_ctx registered on them, but this
+		 * provides for more strict behavior to notice
+		 * unregistration errors.
+		 */
+		if (!vma_can_userfault(cur, cur->vm_flags, wp_async))
+			goto out_unlock;
+
+		found = true;
+	} for_each_vma_range(vmi, cur, end);
+	VM_WARN_ON_ONCE(!found);
+
+	vma_iter_set(&vmi, start);
+	prev = vma_prev(&vmi);
+	if (vma->vm_start < start)
+		prev = vma;
+
+	ret = 0;
+	for_each_vma_range(vmi, vma, end) {
+		cond_resched();
+
+		/* VMA not registered with userfaultfd. */
+		if (!vma->vm_userfaultfd_ctx.ctx)
+			goto skip;
+
+		VM_WARN_ON_ONCE(vma->vm_userfaultfd_ctx.ctx != ctx);
+		VM_WARN_ON_ONCE(!vma_can_userfault(vma, vma->vm_flags, wp_async));
+		VM_WARN_ON_ONCE(!(vma->vm_flags & VM_MAYWRITE));
+
+		if (vma->vm_start > start)
+			start = vma->vm_start;
+		vma_end = min(end, vma->vm_end);
+
+		if (userfaultfd_missing(vma)) {
+			/*
+			 * Wake any concurrent pending userfault while
+			 * we unregister, so they will not hang
+			 * permanently and it avoids userland to call
+			 * UFFDIO_WAKE explicitly.
+			 */
+			struct userfaultfd_wake_range range;
+			range.start = start;
+			range.len = vma_end - start;
+			wake_userfault(vma->vm_userfaultfd_ctx.ctx, &range);
+		}
+
+		vma = userfaultfd_clear_vma(&vmi, prev, vma,
+					    start, vma_end);
+		if (IS_ERR(vma)) {
+			ret = PTR_ERR(vma);
+			break;
+		}
+
+skip:
+		prev = vma;
+		start = vma->vm_end;
+	}
+
+out_unlock:
+	mmap_write_unlock(mm);
+	mmput(mm);
+out:
+	return ret;
+}
+
+/*
+ * userfaultfd_wake may be used in combination with the
+ * UFFDIO_*_MODE_DONTWAKE to wakeup userfaults in batches.
+ */
+static int userfaultfd_wake(struct userfaultfd_ctx *ctx,
+			    unsigned long arg)
+{
+	int ret;
+	struct uffdio_range uffdio_wake;
+	struct userfaultfd_wake_range range;
+	const void __user *buf = (void __user *)arg;
+
+	ret = -EFAULT;
+	if (copy_from_user(&uffdio_wake, buf, sizeof(uffdio_wake)))
+		goto out;
+
+	ret = validate_range(ctx->mm, uffdio_wake.start, uffdio_wake.len);
+	if (ret)
+		goto out;
+
+	range.start = uffdio_wake.start;
+	range.len = uffdio_wake.len;
+
+	/*
+	 * len == 0 means wake all and we don't want to wake all here,
+	 * so check it again to be sure.
+	 */
+	VM_WARN_ON_ONCE(!range.len);
+
+	wake_userfault(ctx, &range);
+	ret = 0;
+
+out:
+	return ret;
+}
+
+static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
+			    unsigned long arg)
+{
+	__s64 ret;
+	struct uffdio_copy uffdio_copy;
+	struct uffdio_copy __user *user_uffdio_copy;
+	struct userfaultfd_wake_range range;
+	uffd_flags_t flags = 0;
+
+	user_uffdio_copy = (struct uffdio_copy __user *) arg;
+
+	ret = -EAGAIN;
+	if (unlikely(atomic_read(&ctx->mmap_changing))) {
+		if (unlikely(put_user(ret, &user_uffdio_copy->copy)))
+			return -EFAULT;
+		goto out;
+	}
+
+	ret = -EFAULT;
+	if (copy_from_user(&uffdio_copy, user_uffdio_copy,
+			   /* don't copy "copy" last field */
+			   sizeof(uffdio_copy)-sizeof(__s64)))
+		goto out;
+
+	ret = validate_unaligned_range(ctx->mm, uffdio_copy.src,
+				       uffdio_copy.len);
+	if (ret)
+		goto out;
+	ret = validate_range(ctx->mm, uffdio_copy.dst, uffdio_copy.len);
+	if (ret)
+		goto out;
+
+	ret = -EINVAL;
+	if (uffdio_copy.mode & ~(UFFDIO_COPY_MODE_DONTWAKE|UFFDIO_COPY_MODE_WP))
+		goto out;
+	if (uffdio_copy.mode & UFFDIO_COPY_MODE_WP)
+		flags |= MFILL_ATOMIC_WP;
+	if (mmget_not_zero(ctx->mm)) {
+		ret = mfill_atomic_copy(ctx, uffdio_copy.dst, uffdio_copy.src,
+					uffdio_copy.len, flags);
+		mmput(ctx->mm);
+	} else {
+		return -ESRCH;
+	}
+	if (unlikely(put_user(ret, &user_uffdio_copy->copy)))
+		return -EFAULT;
+	if (ret < 0)
+		goto out;
+	VM_WARN_ON_ONCE(!ret);
+	/* len == 0 would wake all */
+	range.len = ret;
+	if (!(uffdio_copy.mode & UFFDIO_COPY_MODE_DONTWAKE)) {
+		range.start = uffdio_copy.dst;
+		wake_userfault(ctx, &range);
+	}
+	ret = range.len == uffdio_copy.len ? 0 : -EAGAIN;
+out:
+	return ret;
+}
+
+static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx,
+				unsigned long arg)
+{
+	__s64 ret;
+	struct uffdio_zeropage uffdio_zeropage;
+	struct uffdio_zeropage __user *user_uffdio_zeropage;
+	struct userfaultfd_wake_range range;
+
+	user_uffdio_zeropage = (struct uffdio_zeropage __user *) arg;
+
+	ret = -EAGAIN;
+	if (unlikely(atomic_read(&ctx->mmap_changing))) {
+		if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage)))
+			return -EFAULT;
+		goto out;
+	}
+
+	ret = -EFAULT;
+	if (copy_from_user(&uffdio_zeropage, user_uffdio_zeropage,
+			   /* don't copy "zeropage" last field */
+			   sizeof(uffdio_zeropage)-sizeof(__s64)))
+		goto out;
+
+	ret = validate_range(ctx->mm, uffdio_zeropage.range.start,
+			     uffdio_zeropage.range.len);
+	if (ret)
+		goto out;
+	ret = -EINVAL;
+	if (uffdio_zeropage.mode & ~UFFDIO_ZEROPAGE_MODE_DONTWAKE)
+		goto out;
+
+	if (mmget_not_zero(ctx->mm)) {
+		ret = mfill_atomic_zeropage(ctx, uffdio_zeropage.range.start,
+					    uffdio_zeropage.range.len);
+		mmput(ctx->mm);
+	} else {
+		return -ESRCH;
+	}
+	if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage)))
+		return -EFAULT;
+	if (ret < 0)
+		goto out;
+	/* len == 0 would wake all */
+	VM_WARN_ON_ONCE(!ret);
+	range.len = ret;
+	if (!(uffdio_zeropage.mode & UFFDIO_ZEROPAGE_MODE_DONTWAKE)) {
+		range.start = uffdio_zeropage.range.start;
+		wake_userfault(ctx, &range);
+	}
+	ret = range.len == uffdio_zeropage.range.len ? 0 : -EAGAIN;
+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;
+	bool mode_wp, mode_dontwake;
+
+	if (atomic_read(&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;
+
+	mode_wp = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_WP;
+	mode_dontwake = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_DONTWAKE;
+
+	if (mode_wp && mode_dontwake)
+		return -EINVAL;
+
+	if (mmget_not_zero(ctx->mm)) {
+		ret = mwriteprotect_range(ctx, uffdio_wp.range.start,
+					  uffdio_wp.range.len, mode_wp);
+		mmput(ctx->mm);
+	} else {
+		return -ESRCH;
+	}
+
+	if (ret)
+		return ret;
+
+	if (!mode_wp && !mode_dontwake) {
+		range.start = uffdio_wp.range.start;
+		range.len = uffdio_wp.range.len;
+		wake_userfault(ctx, &range);
+	}
+	return ret;
+}
+
+static int userfaultfd_continue(struct userfaultfd_ctx *ctx, unsigned long arg)
+{
+	__s64 ret;
+	struct uffdio_continue uffdio_continue;
+	struct uffdio_continue __user *user_uffdio_continue;
+	struct userfaultfd_wake_range range;
+	uffd_flags_t flags = 0;
+
+	user_uffdio_continue = (struct uffdio_continue __user *)arg;
+
+	ret = -EAGAIN;
+	if (unlikely(atomic_read(&ctx->mmap_changing))) {
+		if (unlikely(put_user(ret, &user_uffdio_continue->mapped)))
+			return -EFAULT;
+		goto out;
+	}
+
+	ret = -EFAULT;
+	if (copy_from_user(&uffdio_continue, user_uffdio_continue,
+			   /* don't copy the output fields */
+			   sizeof(uffdio_continue) - (sizeof(__s64))))
+		goto out;
+
+	ret = validate_range(ctx->mm, uffdio_continue.range.start,
+			     uffdio_continue.range.len);
+	if (ret)
+		goto out;
+
+	ret = -EINVAL;
+	if (uffdio_continue.mode & ~(UFFDIO_CONTINUE_MODE_DONTWAKE |
+				     UFFDIO_CONTINUE_MODE_WP))
+		goto out;
+	if (uffdio_continue.mode & UFFDIO_CONTINUE_MODE_WP)
+		flags |= MFILL_ATOMIC_WP;
+
+	if (mmget_not_zero(ctx->mm)) {
+		ret = mfill_atomic_continue(ctx, uffdio_continue.range.start,
+					    uffdio_continue.range.len, flags);
+		mmput(ctx->mm);
+	} else {
+		return -ESRCH;
+	}
+
+	if (unlikely(put_user(ret, &user_uffdio_continue->mapped)))
+		return -EFAULT;
+	if (ret < 0)
+		goto out;
+
+	/* len == 0 would wake all */
+	VM_WARN_ON_ONCE(!ret);
+	range.len = ret;
+	if (!(uffdio_continue.mode & UFFDIO_CONTINUE_MODE_DONTWAKE)) {
+		range.start = uffdio_continue.range.start;
+		wake_userfault(ctx, &range);
+	}
+	ret = range.len == uffdio_continue.range.len ? 0 : -EAGAIN;
+
+out:
+	return ret;
+}
+
+static inline int userfaultfd_poison(struct userfaultfd_ctx *ctx, unsigned long arg)
+{
+	__s64 ret;
+	struct uffdio_poison uffdio_poison;
+	struct uffdio_poison __user *user_uffdio_poison;
+	struct userfaultfd_wake_range range;
+
+	user_uffdio_poison = (struct uffdio_poison __user *)arg;
+
+	ret = -EAGAIN;
+	if (unlikely(atomic_read(&ctx->mmap_changing))) {
+		if (unlikely(put_user(ret, &user_uffdio_poison->updated)))
+			return -EFAULT;
+		goto out;
+	}
+
+	ret = -EFAULT;
+	if (copy_from_user(&uffdio_poison, user_uffdio_poison,
+			   /* don't copy the output fields */
+			   sizeof(uffdio_poison) - (sizeof(__s64))))
+		goto out;
+
+	ret = validate_range(ctx->mm, uffdio_poison.range.start,
+			     uffdio_poison.range.len);
+	if (ret)
+		goto out;
+
+	ret = -EINVAL;
+	if (uffdio_poison.mode & ~UFFDIO_POISON_MODE_DONTWAKE)
+		goto out;
+
+	if (mmget_not_zero(ctx->mm)) {
+		ret = mfill_atomic_poison(ctx, uffdio_poison.range.start,
+					  uffdio_poison.range.len, 0);
+		mmput(ctx->mm);
+	} else {
+		return -ESRCH;
+	}
+
+	if (unlikely(put_user(ret, &user_uffdio_poison->updated)))
+		return -EFAULT;
+	if (ret < 0)
+		goto out;
+
+	/* len == 0 would wake all */
+	VM_WARN_ON_ONCE(!ret);
+	range.len = ret;
+	if (!(uffdio_poison.mode & UFFDIO_POISON_MODE_DONTWAKE)) {
+		range.start = uffdio_poison.range.start;
+		wake_userfault(ctx, &range);
+	}
+	ret = range.len == uffdio_poison.range.len ? 0 : -EAGAIN;
+
+out:
+	return ret;
+}
+
+bool userfaultfd_wp_async(struct vm_area_struct *vma)
+{
+	return userfaultfd_wp_async_ctx(vma->vm_userfaultfd_ctx.ctx);
+}
+
+static inline unsigned int uffd_ctx_features(__u64 user_features)
+{
+	/*
+	 * For the current set of features the bits just coincide. Set
+	 * UFFD_FEATURE_INITIALIZED to mark the features as enabled.
+	 */
+	return (unsigned int)user_features | UFFD_FEATURE_INITIALIZED;
+}
+
+static int userfaultfd_move(struct userfaultfd_ctx *ctx,
+			    unsigned long arg)
+{
+	__s64 ret;
+	struct uffdio_move uffdio_move;
+	struct uffdio_move __user *user_uffdio_move;
+	struct userfaultfd_wake_range range;
+	struct mm_struct *mm = ctx->mm;
+
+	user_uffdio_move = (struct uffdio_move __user *) arg;
+
+	ret = -EAGAIN;
+	if (unlikely(atomic_read(&ctx->mmap_changing))) {
+		if (unlikely(put_user(ret, &user_uffdio_move->move)))
+			return -EFAULT;
+		goto out;
+	}
+
+	if (copy_from_user(&uffdio_move, user_uffdio_move,
+			   /* don't copy "move" last field */
+			   sizeof(uffdio_move)-sizeof(__s64)))
+		return -EFAULT;
+
+	/* Do not allow cross-mm moves. */
+	if (mm != current->mm)
+		return -EINVAL;
+
+	ret = validate_range(mm, uffdio_move.dst, uffdio_move.len);
+	if (ret)
+		return ret;
+
+	ret = validate_range(mm, uffdio_move.src, uffdio_move.len);
+	if (ret)
+		return ret;
+
+	if (uffdio_move.mode & ~(UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES|
+				 UFFDIO_MOVE_MODE_DONTWAKE))
+		return -EINVAL;
+
+	if (mmget_not_zero(mm)) {
+		ret = move_pages(ctx, uffdio_move.dst, uffdio_move.src,
+				 uffdio_move.len, uffdio_move.mode);
+		mmput(mm);
+	} else {
+		return -ESRCH;
+	}
+
+	if (unlikely(put_user(ret, &user_uffdio_move->move)))
+		return -EFAULT;
+	if (ret < 0)
+		goto out;
+
+	/* len == 0 would wake all */
+	VM_WARN_ON(!ret);
+	range.len = ret;
+	if (!(uffdio_move.mode & UFFDIO_MOVE_MODE_DONTWAKE)) {
+		range.start = uffdio_move.dst;
+		wake_userfault(ctx, &range);
+	}
+	ret = range.len == uffdio_move.len ? 0 : -EAGAIN;
+
+out:
+	return ret;
+}
+
+/*
+ * userland asks for a certain API version and we return which bits
+ * and ioctl commands are implemented in this kernel for such API
+ * version or -EINVAL if unknown.
+ */
+static int userfaultfd_api(struct userfaultfd_ctx *ctx,
+			   unsigned long arg)
+{
+	struct uffdio_api uffdio_api;
+	void __user *buf = (void __user *)arg;
+	unsigned int ctx_features;
+	int ret;
+	__u64 features;
+
+	ret = -EFAULT;
+	if (copy_from_user(&uffdio_api, buf, sizeof(uffdio_api)))
+		goto out;
+	features = uffdio_api.features;
+	ret = -EINVAL;
+	if (uffdio_api.api != UFFD_API)
+		goto err_out;
+	ret = -EPERM;
+	if ((features & UFFD_FEATURE_EVENT_FORK) && !capable(CAP_SYS_PTRACE))
+		goto err_out;
+
+	/* WP_ASYNC relies on WP_UNPOPULATED, choose it unconditionally */
+	if (features & UFFD_FEATURE_WP_ASYNC)
+		features |= UFFD_FEATURE_WP_UNPOPULATED;
+
+	/* report all available features and ioctls to userland */
+	uffdio_api.features = UFFD_API_FEATURES;
+#ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
+	uffdio_api.features &=
+		~(UFFD_FEATURE_MINOR_HUGETLBFS | UFFD_FEATURE_MINOR_SHMEM);
+#endif
+	if (!pgtable_supports_uffd_wp())
+		uffdio_api.features &= ~UFFD_FEATURE_PAGEFAULT_FLAG_WP;
+
+	if (!uffd_supports_wp_marker()) {
+		uffdio_api.features &= ~UFFD_FEATURE_WP_HUGETLBFS_SHMEM;
+		uffdio_api.features &= ~UFFD_FEATURE_WP_UNPOPULATED;
+		uffdio_api.features &= ~UFFD_FEATURE_WP_ASYNC;
+	}
+
+	ret = -EINVAL;
+	if (features & ~uffdio_api.features)
+		goto err_out;
+
+	uffdio_api.ioctls = UFFD_API_IOCTLS;
+	ret = -EFAULT;
+	if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
+		goto out;
+
+	/* only enable the requested features for this uffd context */
+	ctx_features = uffd_ctx_features(features);
+	ret = -EINVAL;
+	if (cmpxchg(&ctx->features, 0, ctx_features) != 0)
+		goto err_out;
+
+	ret = 0;
+out:
+	return ret;
+err_out:
+	memset(&uffdio_api, 0, sizeof(uffdio_api));
+	if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
+		ret = -EFAULT;
+	goto out;
+}
+
+static long userfaultfd_ioctl(struct file *file, unsigned cmd,
+			      unsigned long arg)
+{
+	int ret = -EINVAL;
+	struct userfaultfd_ctx *ctx = file->private_data;
+
+	if (cmd != UFFDIO_API && !userfaultfd_is_initialized(ctx))
+		return -EINVAL;
+
+	switch (cmd) {
+	case UFFDIO_API:
+		ret = userfaultfd_api(ctx, arg);
+		break;
+	case UFFDIO_REGISTER:
+		ret = userfaultfd_register(ctx, arg);
+		break;
+	case UFFDIO_UNREGISTER:
+		ret = userfaultfd_unregister(ctx, arg);
+		break;
+	case UFFDIO_WAKE:
+		ret = userfaultfd_wake(ctx, arg);
+		break;
+	case UFFDIO_COPY:
+		ret = userfaultfd_copy(ctx, arg);
+		break;
+	case UFFDIO_ZEROPAGE:
+		ret = userfaultfd_zeropage(ctx, arg);
+		break;
+	case UFFDIO_MOVE:
+		ret = userfaultfd_move(ctx, arg);
+		break;
+	case UFFDIO_WRITEPROTECT:
+		ret = userfaultfd_writeprotect(ctx, arg);
+		break;
+	case UFFDIO_CONTINUE:
+		ret = userfaultfd_continue(ctx, arg);
+		break;
+	case UFFDIO_POISON:
+		ret = userfaultfd_poison(ctx, arg);
+		break;
+	}
+	return ret;
+}
+
+#ifdef CONFIG_PROC_FS
+static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f)
+{
+	struct userfaultfd_ctx *ctx = f->private_data;
+	wait_queue_entry_t *wq;
+	unsigned long pending = 0, total = 0;
+
+	spin_lock_irq(&ctx->fault_pending_wqh.lock);
+	list_for_each_entry(wq, &ctx->fault_pending_wqh.head, entry) {
+		pending++;
+		total++;
+	}
+	list_for_each_entry(wq, &ctx->fault_wqh.head, entry) {
+		total++;
+	}
+	spin_unlock_irq(&ctx->fault_pending_wqh.lock);
+
+	/*
+	 * If more protocols will be added, there will be all shown
+	 * separated by a space. Like this:
+	 *	protocols: aa:... bb:...
+	 */
+	seq_printf(m, "pending:\t%lu\ntotal:\t%lu\nAPI:\t%Lx:%x:%Lx\n",
+		   pending, total, UFFD_API, ctx->features,
+		   UFFD_API_IOCTLS|UFFD_API_RANGE_IOCTLS);
+}
+#endif
+
+static const struct file_operations userfaultfd_fops = {
+#ifdef CONFIG_PROC_FS
+	.show_fdinfo	= userfaultfd_show_fdinfo,
+#endif
+	.release	= userfaultfd_release,
+	.poll		= userfaultfd_poll,
+	.read_iter	= userfaultfd_read_iter,
+	.unlocked_ioctl = userfaultfd_ioctl,
+	.compat_ioctl	= compat_ptr_ioctl,
+	.llseek		= noop_llseek,
+};
+
+static void init_once_userfaultfd_ctx(void *mem)
+{
+	struct userfaultfd_ctx *ctx = (struct userfaultfd_ctx *) mem;
+
+	init_waitqueue_head(&ctx->fault_pending_wqh);
+	init_waitqueue_head(&ctx->fault_wqh);
+	init_waitqueue_head(&ctx->event_wqh);
+	init_waitqueue_head(&ctx->fd_wqh);
+	seqcount_spinlock_init(&ctx->refile_seq, &ctx->fault_pending_wqh.lock);
+}
+
+static int new_userfaultfd(int flags)
+{
+	struct userfaultfd_ctx *ctx __free(kfree) = NULL;
+
+	VM_WARN_ON_ONCE(!current->mm);
+
+	/* Check the UFFD_* constants for consistency. */
+	BUILD_BUG_ON(UFFD_USER_MODE_ONLY & UFFD_SHARED_FCNTL_FLAGS);
+
+	if (flags & ~(UFFD_SHARED_FCNTL_FLAGS | UFFD_USER_MODE_ONLY))
+		return -EINVAL;
+
+	ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
+	if (!ctx)
+		return -ENOMEM;
+
+	refcount_set(&ctx->refcount, 1);
+	ctx->flags = flags;
+	ctx->features = 0;
+	ctx->released = false;
+	init_rwsem(&ctx->map_changing_lock);
+	atomic_set(&ctx->mmap_changing, 0);
+	ctx->mm = current->mm;
+
+	FD_PREPARE(fdf, flags & UFFD_SHARED_FCNTL_FLAGS,
+		   anon_inode_create_getfile("[userfaultfd]", &userfaultfd_fops, ctx,
+					     O_RDONLY | (flags & UFFD_SHARED_FCNTL_FLAGS),
+					     NULL));
+	if (fdf.err)
+		return fdf.err;
+
+	/* prevent the mm struct to be freed */
+	mmgrab(ctx->mm);
+	fd_prepare_file(fdf)->f_mode |= FMODE_NOWAIT;
+	retain_and_null_ptr(ctx);
+	return fd_publish(fdf);
+}
+
+static inline bool userfaultfd_syscall_allowed(int flags)
+{
+	/* Userspace-only page faults are always allowed */
+	if (flags & UFFD_USER_MODE_ONLY)
+		return true;
+
+	/*
+	 * The user is requesting a userfaultfd which can handle kernel faults.
+	 * Privileged users are always allowed to do this.
+	 */
+	if (capable(CAP_SYS_PTRACE))
+		return true;
+
+	/* Otherwise, access to kernel fault handling is sysctl controlled. */
+	return sysctl_unprivileged_userfaultfd;
+}
+
+SYSCALL_DEFINE1(userfaultfd, int, flags)
+{
+	if (!userfaultfd_syscall_allowed(flags))
+		return -EPERM;
+
+	return new_userfaultfd(flags);
+}
+
+static long userfaultfd_dev_ioctl(struct file *file, unsigned int cmd, unsigned long flags)
+{
+	if (cmd != USERFAULTFD_IOC_NEW)
+		return -EINVAL;
+
+	return new_userfaultfd(flags);
+}
+
+static const struct file_operations userfaultfd_dev_fops = {
+	.unlocked_ioctl = userfaultfd_dev_ioctl,
+	.compat_ioctl = userfaultfd_dev_ioctl,
+	.owner = THIS_MODULE,
+	.llseek = noop_llseek,
+};
+
+static struct miscdevice userfaultfd_misc = {
+	.minor = MISC_DYNAMIC_MINOR,
+	.name = "userfaultfd",
+	.fops = &userfaultfd_dev_fops
+};
+
+static int __init userfaultfd_init(void)
+{
+	int ret;
+
+	ret = misc_register(&userfaultfd_misc);
+	if (ret)
+		return ret;
+
+	userfaultfd_ctx_cachep = kmem_cache_create("userfaultfd_ctx_cache",
+						sizeof(struct userfaultfd_ctx),
+						0,
+						SLAB_HWCACHE_ALIGN|SLAB_PANIC,
+						init_once_userfaultfd_ctx);
+#ifdef CONFIG_SYSCTL
+	register_sysctl_init("vm", vm_userfaultfd_table);
+#endif
+	return 0;
+}
+__initcall(userfaultfd_init);
-- 
2.53.0