Merge tag 'mm-stable-2024-03-13-20-04' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Pull MM updates from Andrew Morton:

 - Sumanth Korikkar has taught s390 to allocate hotplug-time page frames
   from hotplugged memory rather than only from main memory. Series
   "implement "memmap on memory" feature on s390".

 - More folio conversions from Matthew Wilcox in the series

	"Convert memcontrol charge moving to use folios"
	"mm: convert mm counter to take a folio"

 - Chengming Zhou has optimized zswap's rbtree locking, providing
   significant reductions in system time and modest but measurable
   reductions in overall runtimes. The series is "mm/zswap: optimize the
   scalability of zswap rb-tree".

 - Chengming Zhou has also provided the series "mm/zswap: optimize zswap
   lru list" which provides measurable runtime benefits in some
   swap-intensive situations.

 - And Chengming Zhou further optimizes zswap in the series "mm/zswap:
   optimize for dynamic zswap_pools". Measured improvements are modest.

 - zswap cleanups and simplifications from Yosry Ahmed in the series
   "mm: zswap: simplify zswap_swapoff()".

 - In the series "Add DAX ABI for memmap_on_memory", Vishal Verma has
   contributed several DAX cleanups as well as adding a sysfs tunable to
   control the memmap_on_memory setting when the dax device is
   hotplugged as system memory.

 - Johannes Weiner has added the large series "mm: zswap: cleanups",
   which does that.

 - More DAMON work from SeongJae Park in the series

	"mm/damon: make DAMON debugfs interface deprecation unignorable"
	"selftests/damon: add more tests for core functionalities and corner cases"
	"Docs/mm/damon: misc readability improvements"
	"mm/damon: let DAMOS feeds and tame/auto-tune itself"

 - In the series "mm/mempolicy: weighted interleave mempolicy and sysfs
   extension" Rakie Kim has developed a new mempolicy interleaving
   policy wherein we allocate memory across nodes in a weighted fashion
   rather than uniformly. This is beneficial in heterogeneous memory
   environments appearing with CXL.

 - Christophe Leroy has contributed some cleanup and consolidation work
   against the ARM pagetable dumping code in the series "mm: ptdump:
   Refactor CONFIG_DEBUG_WX and check_wx_pages debugfs attribute".

 - Luis Chamberlain has added some additional xarray selftesting in the
   series "test_xarray: advanced API multi-index tests".

 - Muhammad Usama Anjum has reworked the selftest code to make its
   human-readable output conform to the TAP ("Test Anything Protocol")
   format. Amongst other things, this opens up the use of third-party
   tools to parse and process out selftesting results.

 - Ryan Roberts has added fork()-time PTE batching of THP ptes in the
   series "mm/memory: optimize fork() with PTE-mapped THP". Mainly
   targeted at arm64, this significantly speeds up fork() when the
   process has a large number of pte-mapped folios.

 - David Hildenbrand also gets in on the THP pte batching game in his
   series "mm/memory: optimize unmap/zap with PTE-mapped THP". It
   implements batching during munmap() and other pte teardown
   situations. The microbenchmark improvements are nice.

 - And in the series "Transparent Contiguous PTEs for User Mappings"
   Ryan Roberts further utilizes arm's pte's contiguous bit ("contpte
   mappings"). Kernel build times on arm64 improved nicely. Ryan's
   series "Address some contpte nits" provides some followup work.

 - In the series "mm/hugetlb: Restore the reservation" Breno Leitao has
   fixed an obscure hugetlb race which was causing unnecessary page
   faults. He has also added a reproducer under the selftest code.

 - In the series "selftests/mm: Output cleanups for the compaction
   test", Mark Brown did what the title claims.

 - Kinsey Ho has added the series "mm/mglru: code cleanup and
   refactoring".

 - Even more zswap material from Nhat Pham. The series "fix and extend
   zswap kselftests" does as claimed.

 - In the series "Introduce cpu_dcache_is_aliasing() to fix DAX
   regression" Mathieu Desnoyers has cleaned up and fixed rather a mess
   in our handling of DAX on archiecctures which have virtually aliasing
   data caches. The arm architecture is the main beneficiary.

 - Lokesh Gidra's series "per-vma locks in userfaultfd" provides
   dramatic improvements in worst-case mmap_lock hold times during
   certain userfaultfd operations.

 - Some page_owner enhancements and maintenance work from Oscar Salvador
   in his series

	"page_owner: print stacks and their outstanding allocations"
	"page_owner: Fixup and cleanup"

 - Uladzislau Rezki has contributed some vmalloc scalability
   improvements in his series "Mitigate a vmap lock contention". It
   realizes a 12x improvement for a certain microbenchmark.

 - Some kexec/crash cleanup work from Baoquan He in the series "Split
   crash out from kexec and clean up related config items".

 - Some zsmalloc maintenance work from Chengming Zhou in the series

	"mm/zsmalloc: fix and optimize objects/page migration"
	"mm/zsmalloc: some cleanup for get/set_zspage_mapping()"

 - Zi Yan has taught the MM to perform compaction on folios larger than
   order=0. This a step along the path to implementaton of the merging
   of large anonymous folios. The series is named "Enable >0 order folio
   memory compaction".

 - Christoph Hellwig has done quite a lot of cleanup work in the
   pagecache writeback code in his series "convert write_cache_pages()
   to an iterator".

 - Some modest hugetlb cleanups and speedups in Vishal Moola's series
   "Handle hugetlb faults under the VMA lock".

 - Zi Yan has changed the page splitting code so we can split huge pages
   into sizes other than order-0 to better utilize large folios. The
   series is named "Split a folio to any lower order folios".

 - David Hildenbrand has contributed the series "mm: remove
   total_mapcount()", a cleanup.

 - Matthew Wilcox has sought to improve the performance of bulk memory
   freeing in his series "Rearrange batched folio freeing".

 - Gang Li's series "hugetlb: parallelize hugetlb page init on boot"
   provides large improvements in bootup times on large machines which
   are configured to use large numbers of hugetlb pages.

 - Matthew Wilcox's series "PageFlags cleanups" does that.

 - Qi Zheng's series "minor fixes and supplement for ptdesc" does that
   also. S390 is affected.

 - Cleanups to our pagemap utility functions from Peter Xu in his series
   "mm/treewide: Replace pXd_large() with pXd_leaf()".

 - Nico Pache has fixed a few things with our hugepage selftests in his
   series "selftests/mm: Improve Hugepage Test Handling in MM
   Selftests".

 - Also, of course, many singleton patches to many things. Please see
   the individual changelogs for details.

* tag 'mm-stable-2024-03-13-20-04' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (435 commits)
  mm/zswap: remove the memcpy if acomp is not sleepable
  crypto: introduce: acomp_is_async to expose if comp drivers might sleep
  memtest: use {READ,WRITE}_ONCE in memory scanning
  mm: prohibit the last subpage from reusing the entire large folio
  mm: recover pud_leaf() definitions in nopmd case
  selftests/mm: skip the hugetlb-madvise tests on unmet hugepage requirements
  selftests/mm: skip uffd hugetlb tests with insufficient hugepages
  selftests/mm: dont fail testsuite due to a lack of hugepages
  mm/huge_memory: skip invalid debugfs new_order input for folio split
  mm/huge_memory: check new folio order when split a folio
  mm, vmscan: retry kswapd's priority loop with cache_trim_mode off on failure
  mm: add an explicit smp_wmb() to UFFDIO_CONTINUE
  mm: fix list corruption in put_pages_list
  mm: remove folio from deferred split list before uncharging it
  filemap: avoid unnecessary major faults in filemap_fault()
  mm,page_owner: drop unnecessary check
  mm,page_owner: check for null stack_record before bumping its refcount
  mm: swap: fix race between free_swap_and_cache() and swapoff()
  mm/treewide: align up pXd_leaf() retval across archs
  mm/treewide: drop pXd_large()
  ...

1 files changed, 372 insertions, 121 deletions

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 313f1c42768a..712160cd41ec 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -20,19 +20,11 @@
 #include "internal.h"
 
 static __always_inline
-struct vm_area_struct *find_dst_vma(struct mm_struct *dst_mm,
-				    unsigned long dst_start,
-				    unsigned long len)
+bool validate_dst_vma(struct vm_area_struct *dst_vma, unsigned long dst_end)
 {
-	/*
-	 * Make sure that the dst range is both valid and fully within a
-	 * single existing vma.
-	 */
-	struct vm_area_struct *dst_vma;
-
-	dst_vma = find_vma(dst_mm, dst_start);
-	if (!range_in_vma(dst_vma, dst_start, dst_start + len))
-		return NULL;
+	/* Make sure that the dst range is fully within dst_vma. */
+	if (dst_end > dst_vma->vm_end)
+		return false;
 
 	/*
 	 * Check the vma is registered in uffd, this is required to
@@ -40,11 +32,122 @@ struct vm_area_struct *find_dst_vma(struct mm_struct *dst_mm,
 	 * time.
 	 */
 	if (!dst_vma->vm_userfaultfd_ctx.ctx)
-		return NULL;
+		return false;
+
+	return true;
+}
+
+static __always_inline
+struct vm_area_struct *find_vma_and_prepare_anon(struct mm_struct *mm,
+						 unsigned long addr)
+{
+	struct vm_area_struct *vma;
+
+	mmap_assert_locked(mm);
+	vma = vma_lookup(mm, addr);
+	if (!vma)
+		vma = ERR_PTR(-ENOENT);
+	else if (!(vma->vm_flags & VM_SHARED) &&
+		 unlikely(anon_vma_prepare(vma)))
+		vma = ERR_PTR(-ENOMEM);
+
+	return vma;
+}
+
+#ifdef CONFIG_PER_VMA_LOCK
+/*
+ * lock_vma() - Lookup and lock vma corresponding to @address.
+ * @mm: mm to search vma in.
+ * @address: address that the vma should contain.
+ *
+ * Should be called without holding mmap_lock. vma should be unlocked after use
+ * with unlock_vma().
+ *
+ * Return: A locked vma containing @address, -ENOENT if no vma is found, or
+ * -ENOMEM if anon_vma couldn't be allocated.
+ */
+static struct vm_area_struct *lock_vma(struct mm_struct *mm,
+				       unsigned long address)
+{
+	struct vm_area_struct *vma;
 
+	vma = lock_vma_under_rcu(mm, address);
+	if (vma) {
+		/*
+		 * lock_vma_under_rcu() only checks anon_vma for private
+		 * anonymous mappings. But we need to ensure it is assigned in
+		 * private file-backed vmas as well.
+		 */
+		if (!(vma->vm_flags & VM_SHARED) && unlikely(!vma->anon_vma))
+			vma_end_read(vma);
+		else
+			return vma;
+	}
+
+	mmap_read_lock(mm);
+	vma = find_vma_and_prepare_anon(mm, address);
+	if (!IS_ERR(vma)) {
+		/*
+		 * We cannot use vma_start_read() as it may fail due to
+		 * false locked (see comment in vma_start_read()). We
+		 * can avoid that by directly locking vm_lock under
+		 * mmap_lock, which guarantees that nobody can lock the
+		 * vma for write (vma_start_write()) under us.
+		 */
+		down_read(&vma->vm_lock->lock);
+	}
+
+	mmap_read_unlock(mm);
+	return vma;
+}
+
+static struct vm_area_struct *uffd_mfill_lock(struct mm_struct *dst_mm,
+					      unsigned long dst_start,
+					      unsigned long len)
+{
+	struct vm_area_struct *dst_vma;
+
+	dst_vma = lock_vma(dst_mm, dst_start);
+	if (IS_ERR(dst_vma) || validate_dst_vma(dst_vma, dst_start + len))
+		return dst_vma;
+
+	vma_end_read(dst_vma);
+	return ERR_PTR(-ENOENT);
+}
+
+static void uffd_mfill_unlock(struct vm_area_struct *vma)
+{
+	vma_end_read(vma);
+}
+
+#else
+
+static struct vm_area_struct *uffd_mfill_lock(struct mm_struct *dst_mm,
+					      unsigned long dst_start,
+					      unsigned long len)
+{
+	struct vm_area_struct *dst_vma;
+
+	mmap_read_lock(dst_mm);
+	dst_vma = find_vma_and_prepare_anon(dst_mm, dst_start);
+	if (IS_ERR(dst_vma))
+		goto out_unlock;
+
+	if (validate_dst_vma(dst_vma, dst_start + len))
+		return dst_vma;
+
+	dst_vma = ERR_PTR(-ENOENT);
+out_unlock:
+	mmap_read_unlock(dst_mm);
 	return dst_vma;
 }
 
+static void uffd_mfill_unlock(struct vm_area_struct *vma)
+{
+	mmap_read_unlock(vma->vm_mm);
+}
+#endif
+
 /* Check if dst_addr is outside of file's size. Must be called with ptl held. */
 static bool mfill_file_over_size(struct vm_area_struct *dst_vma,
 				 unsigned long dst_addr)
@@ -124,7 +227,7 @@ int mfill_atomic_install_pte(pmd_t *dst_pmd,
 	 * Must happen after rmap, as mm_counter() checks mapping (via
 	 * PageAnon()), which is set by __page_set_anon_rmap().
 	 */
-	inc_mm_counter(dst_mm, mm_counter(page));
+	inc_mm_counter(dst_mm, mm_counter(folio));
 
 	set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
 
@@ -350,18 +453,18 @@ static pmd_t *mm_alloc_pmd(struct mm_struct *mm, unsigned long address)
 #ifdef CONFIG_HUGETLB_PAGE
 /*
  * mfill_atomic processing for HUGETLB vmas.  Note that this routine is
- * called with mmap_lock held, it will release mmap_lock before returning.
+ * called with either vma-lock or mmap_lock held, it will release the lock
+ * before returning.
  */
 static __always_inline ssize_t mfill_atomic_hugetlb(
+					      struct userfaultfd_ctx *ctx,
 					      struct vm_area_struct *dst_vma,
 					      unsigned long dst_start,
 					      unsigned long src_start,
 					      unsigned long len,
-					      atomic_t *mmap_changing,
 					      uffd_flags_t flags)
 {
 	struct mm_struct *dst_mm = dst_vma->vm_mm;
-	int vm_shared = dst_vma->vm_flags & VM_SHARED;
 	ssize_t err;
 	pte_t *dst_pte;
 	unsigned long src_addr, dst_addr;
@@ -379,7 +482,8 @@ static __always_inline ssize_t mfill_atomic_hugetlb(
 	 * feature is not supported.
 	 */
 	if (uffd_flags_mode_is(flags, MFILL_ATOMIC_ZEROPAGE)) {
-		mmap_read_unlock(dst_mm);
+		up_read(&ctx->map_changing_lock);
+		uffd_mfill_unlock(dst_vma);
 		return -EINVAL;
 	}
 
@@ -402,24 +506,28 @@ retry:
 	 * retry, dst_vma will be set to NULL and we must lookup again.
 	 */
 	if (!dst_vma) {
+		dst_vma = uffd_mfill_lock(dst_mm, dst_start, len);
+		if (IS_ERR(dst_vma)) {
+			err = PTR_ERR(dst_vma);
+			goto out;
+		}
+
 		err = -ENOENT;
-		dst_vma = find_dst_vma(dst_mm, dst_start, len);
-		if (!dst_vma || !is_vm_hugetlb_page(dst_vma))
-			goto out_unlock;
+		if (!is_vm_hugetlb_page(dst_vma))
+			goto out_unlock_vma;
 
 		err = -EINVAL;
 		if (vma_hpagesize != vma_kernel_pagesize(dst_vma))
-			goto out_unlock;
-
-		vm_shared = dst_vma->vm_flags & VM_SHARED;
-	}
+			goto out_unlock_vma;
 
-	/*
-	 * If not shared, ensure the dst_vma has a anon_vma.
-	 */
-	err = -ENOMEM;
-	if (!vm_shared) {
-		if (unlikely(anon_vma_prepare(dst_vma)))
+		/*
+		 * If memory mappings are changing because of non-cooperative
+		 * operation (e.g. mremap) running in parallel, bail out and
+		 * request the user to retry later
+		 */
+		down_read(&ctx->map_changing_lock);
+		err = -EAGAIN;
+		if (atomic_read(&ctx->mmap_changing))
 			goto out_unlock;
 	}
 
@@ -463,7 +571,8 @@ retry:
 		cond_resched();
 
 		if (unlikely(err == -ENOENT)) {
-			mmap_read_unlock(dst_mm);
+			up_read(&ctx->map_changing_lock);
+			uffd_mfill_unlock(dst_vma);
 			BUG_ON(!folio);
 
 			err = copy_folio_from_user(folio,
@@ -472,16 +581,6 @@ retry:
 				err = -EFAULT;
 				goto out;
 			}
-			mmap_read_lock(dst_mm);
-			/*
-			 * If memory mappings are changing because of non-cooperative
-			 * operation (e.g. mremap) running in parallel, bail out and
-			 * request the user to retry later
-			 */
-			if (mmap_changing && atomic_read(mmap_changing)) {
-				err = -EAGAIN;
-				break;
-			}
 
 			dst_vma = NULL;
 			goto retry;
@@ -501,7 +600,9 @@ retry:
 	}
 
 out_unlock:
-	mmap_read_unlock(dst_mm);
+	up_read(&ctx->map_changing_lock);
+out_unlock_vma:
+	uffd_mfill_unlock(dst_vma);
 out:
 	if (folio)
 		folio_put(folio);
@@ -512,11 +613,11 @@ out:
 }
 #else /* !CONFIG_HUGETLB_PAGE */
 /* fail at build time if gcc attempts to use this */
-extern ssize_t mfill_atomic_hugetlb(struct vm_area_struct *dst_vma,
+extern ssize_t mfill_atomic_hugetlb(struct userfaultfd_ctx *ctx,
+				    struct vm_area_struct *dst_vma,
 				    unsigned long dst_start,
 				    unsigned long src_start,
 				    unsigned long len,
-				    atomic_t *mmap_changing,
 				    uffd_flags_t flags);
 #endif /* CONFIG_HUGETLB_PAGE */
 
@@ -564,13 +665,13 @@ static __always_inline ssize_t mfill_atomic_pte(pmd_t *dst_pmd,
 	return err;
 }
 
-static __always_inline ssize_t mfill_atomic(struct mm_struct *dst_mm,
+static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx,
 					    unsigned long dst_start,
 					    unsigned long src_start,
 					    unsigned long len,
-					    atomic_t *mmap_changing,
 					    uffd_flags_t flags)
 {
+	struct mm_struct *dst_mm = ctx->mm;
 	struct vm_area_struct *dst_vma;
 	ssize_t err;
 	pmd_t *dst_pmd;
@@ -593,24 +694,24 @@ static __always_inline ssize_t mfill_atomic(struct mm_struct *dst_mm,
 	copied = 0;
 	folio = NULL;
 retry:
-	mmap_read_lock(dst_mm);
+	/*
+	 * Make sure the vma is not shared, that the dst range is
+	 * both valid and fully within a single existing vma.
+	 */
+	dst_vma = uffd_mfill_lock(dst_mm, dst_start, len);
+	if (IS_ERR(dst_vma)) {
+		err = PTR_ERR(dst_vma);
+		goto out;
+	}
 
 	/*
 	 * If memory mappings are changing because of non-cooperative
 	 * operation (e.g. mremap) running in parallel, bail out and
 	 * request the user to retry later
 	 */
+	down_read(&ctx->map_changing_lock);
 	err = -EAGAIN;
-	if (mmap_changing && atomic_read(mmap_changing))
-		goto out_unlock;
-
-	/*
-	 * Make sure the vma is not shared, that the dst range is
-	 * both valid and fully within a single existing vma.
-	 */
-	err = -ENOENT;
-	dst_vma = find_dst_vma(dst_mm, dst_start, len);
-	if (!dst_vma)
+	if (atomic_read(&ctx->mmap_changing))
 		goto out_unlock;
 
 	err = -EINVAL;
@@ -633,8 +734,8 @@ retry:
 	 * If this is a HUGETLB vma, pass off to appropriate routine
 	 */
 	if (is_vm_hugetlb_page(dst_vma))
-		return  mfill_atomic_hugetlb(dst_vma, dst_start, src_start,
-					     len, mmap_changing, flags);
+		return  mfill_atomic_hugetlb(ctx, dst_vma, dst_start,
+					     src_start, len, flags);
 
 	if (!vma_is_anonymous(dst_vma) && !vma_is_shmem(dst_vma))
 		goto out_unlock;
@@ -642,16 +743,6 @@ retry:
 	    uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE))
 		goto out_unlock;
 
-	/*
-	 * Ensure the dst_vma has a anon_vma or this page
-	 * would get a NULL anon_vma when moved in the
-	 * dst_vma.
-	 */
-	err = -ENOMEM;
-	if (!(dst_vma->vm_flags & VM_SHARED) &&
-	    unlikely(anon_vma_prepare(dst_vma)))
-		goto out_unlock;
-
 	while (src_addr < src_start + len) {
 		pmd_t dst_pmdval;
 
@@ -693,7 +784,8 @@ retry:
 		if (unlikely(err == -ENOENT)) {
 			void *kaddr;
 
-			mmap_read_unlock(dst_mm);
+			up_read(&ctx->map_changing_lock);
+			uffd_mfill_unlock(dst_vma);
 			BUG_ON(!folio);
 
 			kaddr = kmap_local_folio(folio, 0);
@@ -723,7 +815,8 @@ retry:
 	}
 
 out_unlock:
-	mmap_read_unlock(dst_mm);
+	up_read(&ctx->map_changing_lock);
+	uffd_mfill_unlock(dst_vma);
 out:
 	if (folio)
 		folio_put(folio);
@@ -733,34 +826,42 @@ out:
 	return copied ? copied : err;
 }
 
-ssize_t mfill_atomic_copy(struct mm_struct *dst_mm, unsigned long dst_start,
+ssize_t mfill_atomic_copy(struct userfaultfd_ctx *ctx, unsigned long dst_start,
 			  unsigned long src_start, unsigned long len,
-			  atomic_t *mmap_changing, uffd_flags_t flags)
+			  uffd_flags_t flags)
 {
-	return mfill_atomic(dst_mm, dst_start, src_start, len, mmap_changing,
+	return mfill_atomic(ctx, dst_start, src_start, len,
 			    uffd_flags_set_mode(flags, MFILL_ATOMIC_COPY));
 }
 
-ssize_t mfill_atomic_zeropage(struct mm_struct *dst_mm, unsigned long start,
-			      unsigned long len, atomic_t *mmap_changing)
+ssize_t mfill_atomic_zeropage(struct userfaultfd_ctx *ctx,
+			      unsigned long start,
+			      unsigned long len)
 {
-	return mfill_atomic(dst_mm, start, 0, len, mmap_changing,
+	return mfill_atomic(ctx, start, 0, len,
 			    uffd_flags_set_mode(0, MFILL_ATOMIC_ZEROPAGE));
 }
 
-ssize_t mfill_atomic_continue(struct mm_struct *dst_mm, unsigned long start,
-			      unsigned long len, atomic_t *mmap_changing,
-			      uffd_flags_t flags)
+ssize_t mfill_atomic_continue(struct userfaultfd_ctx *ctx, unsigned long start,
+			      unsigned long len, uffd_flags_t flags)
 {
-	return mfill_atomic(dst_mm, start, 0, len, mmap_changing,
+
+	/*
+	 * A caller might reasonably assume that UFFDIO_CONTINUE contains an
+	 * smp_wmb() to ensure that any writes to the about-to-be-mapped page by
+	 * the thread doing the UFFDIO_CONTINUE are guaranteed to be visible to
+	 * subsequent loads from the page through the newly mapped address range.
+	 */
+	smp_wmb();
+
+	return mfill_atomic(ctx, start, 0, len,
 			    uffd_flags_set_mode(flags, MFILL_ATOMIC_CONTINUE));
 }
 
-ssize_t mfill_atomic_poison(struct mm_struct *dst_mm, unsigned long start,
-			    unsigned long len, atomic_t *mmap_changing,
-			    uffd_flags_t flags)
+ssize_t mfill_atomic_poison(struct userfaultfd_ctx *ctx, unsigned long start,
+			    unsigned long len, uffd_flags_t flags)
 {
-	return mfill_atomic(dst_mm, start, 0, len, mmap_changing,
+	return mfill_atomic(ctx, start, 0, len,
 			    uffd_flags_set_mode(flags, MFILL_ATOMIC_POISON));
 }
 
@@ -793,10 +894,10 @@ long uffd_wp_range(struct vm_area_struct *dst_vma,
 	return ret;
 }
 
-int mwriteprotect_range(struct mm_struct *dst_mm, unsigned long start,
-			unsigned long len, bool enable_wp,
-			atomic_t *mmap_changing)
+int mwriteprotect_range(struct userfaultfd_ctx *ctx, unsigned long start,
+			unsigned long len, bool enable_wp)
 {
+	struct mm_struct *dst_mm = ctx->mm;
 	unsigned long end = start + len;
 	unsigned long _start, _end;
 	struct vm_area_struct *dst_vma;
@@ -820,8 +921,9 @@ int mwriteprotect_range(struct mm_struct *dst_mm, unsigned long start,
 	 * operation (e.g. mremap) running in parallel, bail out and
 	 * request the user to retry later
 	 */
+	down_read(&ctx->map_changing_lock);
 	err = -EAGAIN;
-	if (mmap_changing && atomic_read(mmap_changing))
+	if (atomic_read(&ctx->mmap_changing))
 		goto out_unlock;
 
 	err = -ENOENT;
@@ -850,6 +952,7 @@ int mwriteprotect_range(struct mm_struct *dst_mm, unsigned long start,
 		err = 0;
 	}
 out_unlock:
+	up_read(&ctx->map_changing_lock);
 	mmap_read_unlock(dst_mm);
 	return err;
 }
@@ -959,6 +1062,33 @@ static int move_swap_pte(struct mm_struct *mm,
 	return 0;
 }
 
+static int move_zeropage_pte(struct mm_struct *mm,
+			     struct vm_area_struct *dst_vma,
+			     struct vm_area_struct *src_vma,
+			     unsigned long dst_addr, unsigned long src_addr,
+			     pte_t *dst_pte, pte_t *src_pte,
+			     pte_t orig_dst_pte, pte_t orig_src_pte,
+			     spinlock_t *dst_ptl, spinlock_t *src_ptl)
+{
+	pte_t zero_pte;
+
+	double_pt_lock(dst_ptl, src_ptl);
+	if (!pte_same(ptep_get(src_pte), orig_src_pte) ||
+	    !pte_same(ptep_get(dst_pte), orig_dst_pte)) {
+		double_pt_unlock(dst_ptl, src_ptl);
+		return -EAGAIN;
+	}
+
+	zero_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr),
+					 dst_vma->vm_page_prot));
+	ptep_clear_flush(src_vma, src_addr, src_pte);
+	set_pte_at(mm, dst_addr, dst_pte, zero_pte);
+	double_pt_unlock(dst_ptl, src_ptl);
+
+	return 0;
+}
+
+
 /*
  * The mmap_lock for reading is held by the caller. Just move the page
  * from src_pmd to dst_pmd if possible, and return true if succeeded
@@ -1041,6 +1171,14 @@ retry:
 	}
 
 	if (pte_present(orig_src_pte)) {
+		if (is_zero_pfn(pte_pfn(orig_src_pte))) {
+			err = move_zeropage_pte(mm, dst_vma, src_vma,
+					       dst_addr, src_addr, dst_pte, src_pte,
+					       orig_dst_pte, orig_src_pte,
+					       dst_ptl, src_ptl);
+			goto out;
+		}
+
 		/*
 		 * Pin and lock both source folio and anon_vma. Since we are in
 		 * RCU read section, we can't block, so on contention have to
@@ -1224,27 +1362,136 @@ static int validate_move_areas(struct userfaultfd_ctx *ctx,
 	if (!vma_is_anonymous(src_vma) || !vma_is_anonymous(dst_vma))
 		return -EINVAL;
 
+	return 0;
+}
+
+static __always_inline
+int find_vmas_mm_locked(struct mm_struct *mm,
+			unsigned long dst_start,
+			unsigned long src_start,
+			struct vm_area_struct **dst_vmap,
+			struct vm_area_struct **src_vmap)
+{
+	struct vm_area_struct *vma;
+
+	mmap_assert_locked(mm);
+	vma = find_vma_and_prepare_anon(mm, dst_start);
+	if (IS_ERR(vma))
+		return PTR_ERR(vma);
+
+	*dst_vmap = vma;
+	/* Skip finding src_vma if src_start is in dst_vma */
+	if (src_start >= vma->vm_start && src_start < vma->vm_end)
+		goto out_success;
+
+	vma = vma_lookup(mm, src_start);
+	if (!vma)
+		return -ENOENT;
+out_success:
+	*src_vmap = vma;
+	return 0;
+}
+
+#ifdef CONFIG_PER_VMA_LOCK
+static int uffd_move_lock(struct mm_struct *mm,
+			  unsigned long dst_start,
+			  unsigned long src_start,
+			  struct vm_area_struct **dst_vmap,
+			  struct vm_area_struct **src_vmap)
+{
+	struct vm_area_struct *vma;
+	int err;
+
+	vma = lock_vma(mm, dst_start);
+	if (IS_ERR(vma))
+		return PTR_ERR(vma);
+
+	*dst_vmap = vma;
 	/*
-	 * Ensure the dst_vma has a anon_vma or this page
-	 * would get a NULL anon_vma when moved in the
-	 * dst_vma.
+	 * Skip finding src_vma if src_start is in dst_vma. This also ensures
+	 * that we don't lock the same vma twice.
 	 */
-	if (unlikely(anon_vma_prepare(dst_vma)))
-		return -ENOMEM;
+	if (src_start >= vma->vm_start && src_start < vma->vm_end) {
+		*src_vmap = vma;
+		return 0;
+	}
 
-	return 0;
+	/*
+	 * Using lock_vma() to get src_vma can lead to following deadlock:
+	 *
+	 * Thread1				Thread2
+	 * -------				-------
+	 * vma_start_read(dst_vma)
+	 *					mmap_write_lock(mm)
+	 *					vma_start_write(src_vma)
+	 * vma_start_read(src_vma)
+	 * mmap_read_lock(mm)
+	 *					vma_start_write(dst_vma)
+	 */
+	*src_vmap = lock_vma_under_rcu(mm, src_start);
+	if (likely(*src_vmap))
+		return 0;
+
+	/* Undo any locking and retry in mmap_lock critical section */
+	vma_end_read(*dst_vmap);
+
+	mmap_read_lock(mm);
+	err = find_vmas_mm_locked(mm, dst_start, src_start, dst_vmap, src_vmap);
+	if (!err) {
+		/*
+		 * See comment in lock_vma() as to why not using
+		 * vma_start_read() here.
+		 */
+		down_read(&(*dst_vmap)->vm_lock->lock);
+		if (*dst_vmap != *src_vmap)
+			down_read(&(*src_vmap)->vm_lock->lock);
+	}
+	mmap_read_unlock(mm);
+	return err;
+}
+
+static void uffd_move_unlock(struct vm_area_struct *dst_vma,
+			     struct vm_area_struct *src_vma)
+{
+	vma_end_read(src_vma);
+	if (src_vma != dst_vma)
+		vma_end_read(dst_vma);
+}
+
+#else
+
+static int uffd_move_lock(struct mm_struct *mm,
+			  unsigned long dst_start,
+			  unsigned long src_start,
+			  struct vm_area_struct **dst_vmap,
+			  struct vm_area_struct **src_vmap)
+{
+	int err;
+
+	mmap_read_lock(mm);
+	err = find_vmas_mm_locked(mm, dst_start, src_start, dst_vmap, src_vmap);
+	if (err)
+		mmap_read_unlock(mm);
+	return err;
+}
+
+static void uffd_move_unlock(struct vm_area_struct *dst_vma,
+			     struct vm_area_struct *src_vma)
+{
+	mmap_assert_locked(src_vma->vm_mm);
+	mmap_read_unlock(dst_vma->vm_mm);
 }
+#endif
 
 /**
  * move_pages - move arbitrary anonymous pages of an existing vma
  * @ctx: pointer to the userfaultfd context
- * @mm: the address space to move pages
  * @dst_start: start of the destination virtual memory range
  * @src_start: start of the source virtual memory range
  * @len: length of the virtual memory range
  * @mode: flags from uffdio_move.mode
  *
- * Must be called with mmap_lock held for read.
+ * It will either use the mmap_lock in read mode or per-vma locks
  *
  * move_pages() remaps arbitrary anonymous pages atomically in zero
  * copy. It only works on non shared anonymous pages because those can
@@ -1312,10 +1559,10 @@ static int validate_move_areas(struct userfaultfd_ctx *ctx,
  * could be obtained. This is the only additional complexity added to
  * the rmap code to provide this anonymous page remapping functionality.
  */
-ssize_t move_pages(struct userfaultfd_ctx *ctx, struct mm_struct *mm,
-		   unsigned long dst_start, unsigned long src_start,
-		   unsigned long len, __u64 mode)
+ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start,
+		   unsigned long src_start, unsigned long len, __u64 mode)
 {
+	struct mm_struct *mm = ctx->mm;
 	struct vm_area_struct *src_vma, *dst_vma;
 	unsigned long src_addr, dst_addr;
 	pmd_t *src_pmd, *dst_pmd;
@@ -1333,28 +1580,34 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, struct mm_struct *mm,
 	    WARN_ON_ONCE(dst_start + len <= dst_start))
 		goto out;
 
+	err = uffd_move_lock(mm, dst_start, src_start, &dst_vma, &src_vma);
+	if (err)
+		goto out;
+
+	/* Re-check after taking map_changing_lock */
+	err = -EAGAIN;
+	down_read(&ctx->map_changing_lock);
+	if (likely(atomic_read(&ctx->mmap_changing)))
+		goto out_unlock;
 	/*
 	 * Make sure the vma is not shared, that the src and dst remap
 	 * ranges are both valid and fully within a single existing
 	 * vma.
 	 */
-	src_vma = find_vma(mm, src_start);
-	if (!src_vma || (src_vma->vm_flags & VM_SHARED))
-		goto out;
-	if (src_start < src_vma->vm_start ||
-	    src_start + len > src_vma->vm_end)
-		goto out;
+	err = -EINVAL;
+	if (src_vma->vm_flags & VM_SHARED)
+		goto out_unlock;
+	if (src_start + len > src_vma->vm_end)
+		goto out_unlock;
 
-	dst_vma = find_vma(mm, dst_start);
-	if (!dst_vma || (dst_vma->vm_flags & VM_SHARED))
-		goto out;
-	if (dst_start < dst_vma->vm_start ||
-	    dst_start + len > dst_vma->vm_end)
-		goto out;
+	if (dst_vma->vm_flags & VM_SHARED)
+		goto out_unlock;
+	if (dst_start + len > dst_vma->vm_end)
+		goto out_unlock;
 
 	err = validate_move_areas(ctx, src_vma, dst_vma);
 	if (err)
-		goto out;
+		goto out_unlock;
 
 	for (src_addr = src_start, dst_addr = dst_start;
 	     src_addr < src_start + len;) {
@@ -1404,19 +1657,14 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, struct mm_struct *mm,
 				err = -ENOENT;
 				break;
 			}
-			/* Avoid moving zeropages for now */
-			if (is_huge_zero_pmd(*src_pmd)) {
-				spin_unlock(ptl);
-				err = -EBUSY;
-				break;
-			}
 
 			/* Check if we can move the pmd without splitting it. */
 			if (move_splits_huge_pmd(dst_addr, src_addr, src_start + len) ||
 			    !pmd_none(dst_pmdval)) {
 				struct folio *folio = pfn_folio(pmd_pfn(*src_pmd));
 
-				if (!folio || !PageAnonExclusive(&folio->page)) {
+				if (!folio || (!is_huge_zero_page(&folio->page) &&
+					       !PageAnonExclusive(&folio->page))) {
 					spin_unlock(ptl);
 					err = -EBUSY;
 					break;
@@ -1476,6 +1724,9 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, struct mm_struct *mm,
 		moved += step_size;
 	}
 
+out_unlock:
+	up_read(&ctx->map_changing_lock);
+	uffd_move_unlock(dst_vma, src_vma);
 out:
 	VM_WARN_ON(moved < 0);
 	VM_WARN_ON(err > 0);