1 files changed, 1016 insertions, 0 deletions

diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
new file mode 100644
index 000000000000..fdaea3422c30
--- /dev/null
+++ b/virt/kvm/guest_memfd.c
@@ -0,0 +1,1016 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/anon_inodes.h>
+#include <linux/backing-dev.h>
+#include <linux/falloc.h>
+#include <linux/fs.h>
+#include <linux/kvm_host.h>
+#include <linux/mempolicy.h>
+#include <linux/pseudo_fs.h>
+#include <linux/pagemap.h>
+
+#include "kvm_mm.h"
+
+static struct vfsmount *kvm_gmem_mnt;
+
+/*
+ * A guest_memfd instance can be associated multiple VMs, each with its own
+ * "view" of the underlying physical memory.
+ *
+ * The gmem's inode is effectively the raw underlying physical storage, and is
+ * used to track properties of the physical memory, while each gmem file is
+ * effectively a single VM's view of that storage, and is used to track assets
+ * specific to its associated VM, e.g. memslots=>gmem bindings.
+ */
+struct gmem_file {
+	struct kvm *kvm;
+	struct xarray bindings;
+	struct list_head entry;
+};
+
+struct gmem_inode {
+	struct shared_policy policy;
+	struct inode vfs_inode;
+
+	u64 flags;
+};
+
+static __always_inline struct gmem_inode *GMEM_I(struct inode *inode)
+{
+	return container_of(inode, struct gmem_inode, vfs_inode);
+}
+
+#define kvm_gmem_for_each_file(f, mapping) \
+	list_for_each_entry(f, &(mapping)->i_private_list, entry)
+
+/**
+ * folio_file_pfn - like folio_file_page, but return a pfn.
+ * @folio: The folio which contains this index.
+ * @index: The index we want to look up.
+ *
+ * Return: The pfn for this index.
+ */
+static inline kvm_pfn_t folio_file_pfn(struct folio *folio, pgoff_t index)
+{
+	return folio_pfn(folio) + (index & (folio_nr_pages(folio) - 1));
+}
+
+static pgoff_t kvm_gmem_get_index(struct kvm_memory_slot *slot, gfn_t gfn)
+{
+	return gfn - slot->base_gfn + slot->gmem.pgoff;
+}
+
+static int __kvm_gmem_prepare_folio(struct kvm *kvm, struct kvm_memory_slot *slot,
+				    pgoff_t index, struct folio *folio)
+{
+#ifdef CONFIG_HAVE_KVM_ARCH_GMEM_PREPARE
+	kvm_pfn_t pfn = folio_file_pfn(folio, index);
+	gfn_t gfn = slot->base_gfn + index - slot->gmem.pgoff;
+	int rc = kvm_arch_gmem_prepare(kvm, gfn, pfn, folio_order(folio));
+	if (rc) {
+		pr_warn_ratelimited("gmem: Failed to prepare folio for index %lx GFN %llx PFN %llx error %d.\n",
+				    index, gfn, pfn, rc);
+		return rc;
+	}
+#endif
+
+	return 0;
+}
+
+static inline void kvm_gmem_mark_prepared(struct folio *folio)
+{
+	folio_mark_uptodate(folio);
+}
+
+/*
+ * Process @folio, which contains @gfn, so that the guest can use it.
+ * The folio must be locked and the gfn must be contained in @slot.
+ * On successful return the guest sees a zero page so as to avoid
+ * leaking host data and the up-to-date flag is set.
+ */
+static int kvm_gmem_prepare_folio(struct kvm *kvm, struct kvm_memory_slot *slot,
+				  gfn_t gfn, struct folio *folio)
+{
+	unsigned long nr_pages, i;
+	pgoff_t index;
+	int r;
+
+	nr_pages = folio_nr_pages(folio);
+	for (i = 0; i < nr_pages; i++)
+		clear_highpage(folio_page(folio, i));
+
+	/*
+	 * Preparing huge folios should always be safe, since it should
+	 * be possible to split them later if needed.
+	 *
+	 * Right now the folio order is always going to be zero, but the
+	 * code is ready for huge folios.  The only assumption is that
+	 * the base pgoff of memslots is naturally aligned with the
+	 * requested page order, ensuring that huge folios can also use
+	 * huge page table entries for GPA->HPA mapping.
+	 *
+	 * The order will be passed when creating the guest_memfd, and
+	 * checked when creating memslots.
+	 */
+	WARN_ON(!IS_ALIGNED(slot->gmem.pgoff, folio_nr_pages(folio)));
+	index = kvm_gmem_get_index(slot, gfn);
+	index = ALIGN_DOWN(index, folio_nr_pages(folio));
+	r = __kvm_gmem_prepare_folio(kvm, slot, index, folio);
+	if (!r)
+		kvm_gmem_mark_prepared(folio);
+
+	return r;
+}
+
+/*
+ * Returns a locked folio on success.  The caller is responsible for
+ * setting the up-to-date flag before the memory is mapped into the guest.
+ * There is no backing storage for the memory, so the folio will remain
+ * up-to-date until it's removed.
+ *
+ * Ignore accessed, referenced, and dirty flags.  The memory is
+ * unevictable and there is no storage to write back to.
+ */
+static struct folio *kvm_gmem_get_folio(struct inode *inode, pgoff_t index)
+{
+	/* TODO: Support huge pages. */
+	struct mempolicy *policy;
+	struct folio *folio;
+
+	/*
+	 * Fast-path: See if folio is already present in mapping to avoid
+	 * policy_lookup.
+	 */
+	folio = __filemap_get_folio(inode->i_mapping, index,
+				    FGP_LOCK | FGP_ACCESSED, 0);
+	if (!IS_ERR(folio))
+		return folio;
+
+	policy = mpol_shared_policy_lookup(&GMEM_I(inode)->policy, index);
+	folio = __filemap_get_folio_mpol(inode->i_mapping, index,
+					 FGP_LOCK | FGP_ACCESSED | FGP_CREAT,
+					 mapping_gfp_mask(inode->i_mapping), policy);
+	mpol_cond_put(policy);
+
+	return folio;
+}
+
+static enum kvm_gfn_range_filter kvm_gmem_get_invalidate_filter(struct inode *inode)
+{
+	if (GMEM_I(inode)->flags & GUEST_MEMFD_FLAG_INIT_SHARED)
+		return KVM_FILTER_SHARED;
+
+	return KVM_FILTER_PRIVATE;
+}
+
+static void __kvm_gmem_invalidate_begin(struct gmem_file *f, pgoff_t start,
+					pgoff_t end,
+					enum kvm_gfn_range_filter attr_filter)
+{
+	bool flush = false, found_memslot = false;
+	struct kvm_memory_slot *slot;
+	struct kvm *kvm = f->kvm;
+	unsigned long index;
+
+	xa_for_each_range(&f->bindings, index, slot, start, end - 1) {
+		pgoff_t pgoff = slot->gmem.pgoff;
+
+		struct kvm_gfn_range gfn_range = {
+			.start = slot->base_gfn + max(pgoff, start) - pgoff,
+			.end = slot->base_gfn + min(pgoff + slot->npages, end) - pgoff,
+			.slot = slot,
+			.may_block = true,
+			.attr_filter = attr_filter,
+		};
+
+		if (!found_memslot) {
+			found_memslot = true;
+
+			KVM_MMU_LOCK(kvm);
+			kvm_mmu_invalidate_begin(kvm);
+		}
+
+		flush |= kvm_mmu_unmap_gfn_range(kvm, &gfn_range);
+	}
+
+	if (flush)
+		kvm_flush_remote_tlbs(kvm);
+
+	if (found_memslot)
+		KVM_MMU_UNLOCK(kvm);
+}
+
+static void kvm_gmem_invalidate_begin(struct inode *inode, pgoff_t start,
+				      pgoff_t end)
+{
+	enum kvm_gfn_range_filter attr_filter;
+	struct gmem_file *f;
+
+	attr_filter = kvm_gmem_get_invalidate_filter(inode);
+
+	kvm_gmem_for_each_file(f, inode->i_mapping)
+		__kvm_gmem_invalidate_begin(f, start, end, attr_filter);
+}
+
+static void __kvm_gmem_invalidate_end(struct gmem_file *f, pgoff_t start,
+				      pgoff_t end)
+{
+	struct kvm *kvm = f->kvm;
+
+	if (xa_find(&f->bindings, &start, end - 1, XA_PRESENT)) {
+		KVM_MMU_LOCK(kvm);
+		kvm_mmu_invalidate_end(kvm);
+		KVM_MMU_UNLOCK(kvm);
+	}
+}
+
+static void kvm_gmem_invalidate_end(struct inode *inode, pgoff_t start,
+				    pgoff_t end)
+{
+	struct gmem_file *f;
+
+	kvm_gmem_for_each_file(f, inode->i_mapping)
+		__kvm_gmem_invalidate_end(f, start, end);
+}
+
+static long kvm_gmem_punch_hole(struct inode *inode, loff_t offset, loff_t len)
+{
+	pgoff_t start = offset >> PAGE_SHIFT;
+	pgoff_t end = (offset + len) >> PAGE_SHIFT;
+
+	/*
+	 * Bindings must be stable across invalidation to ensure the start+end
+	 * are balanced.
+	 */
+	filemap_invalidate_lock(inode->i_mapping);
+
+	kvm_gmem_invalidate_begin(inode, start, end);
+
+	truncate_inode_pages_range(inode->i_mapping, offset, offset + len - 1);
+
+	kvm_gmem_invalidate_end(inode, start, end);
+
+	filemap_invalidate_unlock(inode->i_mapping);
+
+	return 0;
+}
+
+static long kvm_gmem_allocate(struct inode *inode, loff_t offset, loff_t len)
+{
+	struct address_space *mapping = inode->i_mapping;
+	pgoff_t start, index, end;
+	int r;
+
+	/* Dedicated guest is immutable by default. */
+	if (offset + len > i_size_read(inode))
+		return -EINVAL;
+
+	filemap_invalidate_lock_shared(mapping);
+
+	start = offset >> PAGE_SHIFT;
+	end = (offset + len) >> PAGE_SHIFT;
+
+	r = 0;
+	for (index = start; index < end; ) {
+		struct folio *folio;
+
+		if (signal_pending(current)) {
+			r = -EINTR;
+			break;
+		}
+
+		folio = kvm_gmem_get_folio(inode, index);
+		if (IS_ERR(folio)) {
+			r = PTR_ERR(folio);
+			break;
+		}
+
+		index = folio_next_index(folio);
+
+		folio_unlock(folio);
+		folio_put(folio);
+
+		/* 64-bit only, wrapping the index should be impossible. */
+		if (WARN_ON_ONCE(!index))
+			break;
+
+		cond_resched();
+	}
+
+	filemap_invalidate_unlock_shared(mapping);
+
+	return r;
+}
+
+static long kvm_gmem_fallocate(struct file *file, int mode, loff_t offset,
+			       loff_t len)
+{
+	int ret;
+
+	if (!(mode & FALLOC_FL_KEEP_SIZE))
+		return -EOPNOTSUPP;
+
+	if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
+		return -EOPNOTSUPP;
+
+	if (!PAGE_ALIGNED(offset) || !PAGE_ALIGNED(len))
+		return -EINVAL;
+
+	if (mode & FALLOC_FL_PUNCH_HOLE)
+		ret = kvm_gmem_punch_hole(file_inode(file), offset, len);
+	else
+		ret = kvm_gmem_allocate(file_inode(file), offset, len);
+
+	if (!ret)
+		file_modified(file);
+	return ret;
+}
+
+static int kvm_gmem_release(struct inode *inode, struct file *file)
+{
+	struct gmem_file *f = file->private_data;
+	struct kvm_memory_slot *slot;
+	struct kvm *kvm = f->kvm;
+	unsigned long index;
+
+	/*
+	 * Prevent concurrent attempts to *unbind* a memslot.  This is the last
+	 * reference to the file and thus no new bindings can be created, but
+	 * dereferencing the slot for existing bindings needs to be protected
+	 * against memslot updates, specifically so that unbind doesn't race
+	 * and free the memslot (kvm_gmem_get_file() will return NULL).
+	 *
+	 * Since .release is called only when the reference count is zero,
+	 * after which file_ref_get() and get_file_active() fail,
+	 * kvm_gmem_get_pfn() cannot be using the file concurrently.
+	 * file_ref_put() provides a full barrier, and get_file_active() the
+	 * matching acquire barrier.
+	 */
+	mutex_lock(&kvm->slots_lock);
+
+	filemap_invalidate_lock(inode->i_mapping);
+
+	xa_for_each(&f->bindings, index, slot)
+		WRITE_ONCE(slot->gmem.file, NULL);
+
+	/*
+	 * All in-flight operations are gone and new bindings can be created.
+	 * Zap all SPTEs pointed at by this file.  Do not free the backing
+	 * memory, as its lifetime is associated with the inode, not the file.
+	 */
+	__kvm_gmem_invalidate_begin(f, 0, -1ul,
+				    kvm_gmem_get_invalidate_filter(inode));
+	__kvm_gmem_invalidate_end(f, 0, -1ul);
+
+	list_del(&f->entry);
+
+	filemap_invalidate_unlock(inode->i_mapping);
+
+	mutex_unlock(&kvm->slots_lock);
+
+	xa_destroy(&f->bindings);
+	kfree(f);
+
+	kvm_put_kvm(kvm);
+
+	return 0;
+}
+
+static inline struct file *kvm_gmem_get_file(struct kvm_memory_slot *slot)
+{
+	/*
+	 * Do not return slot->gmem.file if it has already been closed;
+	 * there might be some time between the last fput() and when
+	 * kvm_gmem_release() clears slot->gmem.file.
+	 */
+	return get_file_active(&slot->gmem.file);
+}
+
+DEFINE_CLASS(gmem_get_file, struct file *, if (_T) fput(_T),
+	     kvm_gmem_get_file(slot), struct kvm_memory_slot *slot);
+
+static bool kvm_gmem_supports_mmap(struct inode *inode)
+{
+	return GMEM_I(inode)->flags & GUEST_MEMFD_FLAG_MMAP;
+}
+
+static vm_fault_t kvm_gmem_fault_user_mapping(struct vm_fault *vmf)
+{
+	struct inode *inode = file_inode(vmf->vma->vm_file);
+	struct folio *folio;
+	vm_fault_t ret = VM_FAULT_LOCKED;
+
+	if (((loff_t)vmf->pgoff << PAGE_SHIFT) >= i_size_read(inode))
+		return VM_FAULT_SIGBUS;
+
+	if (!(GMEM_I(inode)->flags & GUEST_MEMFD_FLAG_INIT_SHARED))
+		return VM_FAULT_SIGBUS;
+
+	folio = kvm_gmem_get_folio(inode, vmf->pgoff);
+	if (IS_ERR(folio)) {
+		if (PTR_ERR(folio) == -EAGAIN)
+			return VM_FAULT_RETRY;
+
+		return vmf_error(PTR_ERR(folio));
+	}
+
+	if (WARN_ON_ONCE(folio_test_large(folio))) {
+		ret = VM_FAULT_SIGBUS;
+		goto out_folio;
+	}
+
+	if (!folio_test_uptodate(folio)) {
+		clear_highpage(folio_page(folio, 0));
+		kvm_gmem_mark_prepared(folio);
+	}
+
+	vmf->page = folio_file_page(folio, vmf->pgoff);
+
+out_folio:
+	if (ret != VM_FAULT_LOCKED) {
+		folio_unlock(folio);
+		folio_put(folio);
+	}
+
+	return ret;
+}
+
+#ifdef CONFIG_NUMA
+static int kvm_gmem_set_policy(struct vm_area_struct *vma, struct mempolicy *mpol)
+{
+	struct inode *inode = file_inode(vma->vm_file);
+
+	return mpol_set_shared_policy(&GMEM_I(inode)->policy, vma, mpol);
+}
+
+static struct mempolicy *kvm_gmem_get_policy(struct vm_area_struct *vma,
+					     unsigned long addr, pgoff_t *pgoff)
+{
+	struct inode *inode = file_inode(vma->vm_file);
+
+	*pgoff = vma->vm_pgoff + ((addr - vma->vm_start) >> PAGE_SHIFT);
+
+	/*
+	 * Return the memory policy for this index, or NULL if none is set.
+	 *
+	 * Returning NULL, e.g. instead of the current task's memory policy, is
+	 * important for the .get_policy kernel ABI: it indicates that no
+	 * explicit policy has been set via mbind() for this memory. The caller
+	 * can then replace NULL with the default memory policy instead of the
+	 * current task's memory policy.
+	 */
+	return mpol_shared_policy_lookup(&GMEM_I(inode)->policy, *pgoff);
+}
+#endif /* CONFIG_NUMA */
+
+static const struct vm_operations_struct kvm_gmem_vm_ops = {
+	.fault		= kvm_gmem_fault_user_mapping,
+#ifdef CONFIG_NUMA
+	.get_policy	= kvm_gmem_get_policy,
+	.set_policy	= kvm_gmem_set_policy,
+#endif
+};
+
+static int kvm_gmem_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	if (!kvm_gmem_supports_mmap(file_inode(file)))
+		return -ENODEV;
+
+	if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) !=
+	    (VM_SHARED | VM_MAYSHARE)) {
+		return -EINVAL;
+	}
+
+	vma->vm_ops = &kvm_gmem_vm_ops;
+
+	return 0;
+}
+
+static struct file_operations kvm_gmem_fops = {
+	.mmap		= kvm_gmem_mmap,
+	.open		= generic_file_open,
+	.release	= kvm_gmem_release,
+	.fallocate	= kvm_gmem_fallocate,
+};
+
+static int kvm_gmem_migrate_folio(struct address_space *mapping,
+				  struct folio *dst, struct folio *src,
+				  enum migrate_mode mode)
+{
+	WARN_ON_ONCE(1);
+	return -EINVAL;
+}
+
+static int kvm_gmem_error_folio(struct address_space *mapping, struct folio *folio)
+{
+	pgoff_t start, end;
+
+	filemap_invalidate_lock_shared(mapping);
+
+	start = folio->index;
+	end = start + folio_nr_pages(folio);
+
+	kvm_gmem_invalidate_begin(mapping->host, start, end);
+
+	/*
+	 * Do not truncate the range, what action is taken in response to the
+	 * error is userspace's decision (assuming the architecture supports
+	 * gracefully handling memory errors).  If/when the guest attempts to
+	 * access a poisoned page, kvm_gmem_get_pfn() will return -EHWPOISON,
+	 * at which point KVM can either terminate the VM or propagate the
+	 * error to userspace.
+	 */
+
+	kvm_gmem_invalidate_end(mapping->host, start, end);
+
+	filemap_invalidate_unlock_shared(mapping);
+
+	return MF_DELAYED;
+}
+
+#ifdef CONFIG_HAVE_KVM_ARCH_GMEM_INVALIDATE
+static void kvm_gmem_free_folio(struct folio *folio)
+{
+	struct page *page = folio_page(folio, 0);
+	kvm_pfn_t pfn = page_to_pfn(page);
+	int order = folio_order(folio);
+
+	kvm_arch_gmem_invalidate(pfn, pfn + (1ul << order));
+}
+#endif
+
+static const struct address_space_operations kvm_gmem_aops = {
+	.dirty_folio = noop_dirty_folio,
+	.migrate_folio	= kvm_gmem_migrate_folio,
+	.error_remove_folio = kvm_gmem_error_folio,
+#ifdef CONFIG_HAVE_KVM_ARCH_GMEM_INVALIDATE
+	.free_folio = kvm_gmem_free_folio,
+#endif
+};
+
+static int kvm_gmem_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
+			    struct iattr *attr)
+{
+	return -EINVAL;
+}
+static const struct inode_operations kvm_gmem_iops = {
+	.setattr	= kvm_gmem_setattr,
+};
+
+bool __weak kvm_arch_supports_gmem_init_shared(struct kvm *kvm)
+{
+	return true;
+}
+
+static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags)
+{
+	static const char *name = "[kvm-gmem]";
+	struct gmem_file *f;
+	struct inode *inode;
+	struct file *file;
+	int fd, err;
+
+	fd = get_unused_fd_flags(0);
+	if (fd < 0)
+		return fd;
+
+	f = kzalloc(sizeof(*f), GFP_KERNEL);
+	if (!f) {
+		err = -ENOMEM;
+		goto err_fd;
+	}
+
+	/* __fput() will take care of fops_put(). */
+	if (!fops_get(&kvm_gmem_fops)) {
+		err = -ENOENT;
+		goto err_gmem;
+	}
+
+	inode = anon_inode_make_secure_inode(kvm_gmem_mnt->mnt_sb, name, NULL);
+	if (IS_ERR(inode)) {
+		err = PTR_ERR(inode);
+		goto err_fops;
+	}
+
+	inode->i_op = &kvm_gmem_iops;
+	inode->i_mapping->a_ops = &kvm_gmem_aops;
+	inode->i_mode |= S_IFREG;
+	inode->i_size = size;
+	mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
+	mapping_set_inaccessible(inode->i_mapping);
+	/* Unmovable mappings are supposed to be marked unevictable as well. */
+	WARN_ON_ONCE(!mapping_unevictable(inode->i_mapping));
+
+	GMEM_I(inode)->flags = flags;
+
+	file = alloc_file_pseudo(inode, kvm_gmem_mnt, name, O_RDWR, &kvm_gmem_fops);
+	if (IS_ERR(file)) {
+		err = PTR_ERR(file);
+		goto err_inode;
+	}
+
+	file->f_flags |= O_LARGEFILE;
+	file->private_data = f;
+
+	kvm_get_kvm(kvm);
+	f->kvm = kvm;
+	xa_init(&f->bindings);
+	list_add(&f->entry, &inode->i_mapping->i_private_list);
+
+	fd_install(fd, file);
+	return fd;
+
+err_inode:
+	iput(inode);
+err_fops:
+	fops_put(&kvm_gmem_fops);
+err_gmem:
+	kfree(f);
+err_fd:
+	put_unused_fd(fd);
+	return err;
+}
+
+int kvm_gmem_create(struct kvm *kvm, struct kvm_create_guest_memfd *args)
+{
+	loff_t size = args->size;
+	u64 flags = args->flags;
+
+	if (flags & ~kvm_gmem_get_supported_flags(kvm))
+		return -EINVAL;
+
+	if (size <= 0 || !PAGE_ALIGNED(size))
+		return -EINVAL;
+
+	return __kvm_gmem_create(kvm, size, flags);
+}
+
+int kvm_gmem_bind(struct kvm *kvm, struct kvm_memory_slot *slot,
+		  unsigned int fd, loff_t offset)
+{
+	loff_t size = slot->npages << PAGE_SHIFT;
+	unsigned long start, end;
+	struct gmem_file *f;
+	struct inode *inode;
+	struct file *file;
+	int r = -EINVAL;
+
+	BUILD_BUG_ON(sizeof(gfn_t) != sizeof(slot->gmem.pgoff));
+
+	file = fget(fd);
+	if (!file)
+		return -EBADF;
+
+	if (file->f_op != &kvm_gmem_fops)
+		goto err;
+
+	f = file->private_data;
+	if (f->kvm != kvm)
+		goto err;
+
+	inode = file_inode(file);
+
+	if (offset < 0 || !PAGE_ALIGNED(offset) ||
+	    offset + size > i_size_read(inode))
+		goto err;
+
+	filemap_invalidate_lock(inode->i_mapping);
+
+	start = offset >> PAGE_SHIFT;
+	end = start + slot->npages;
+
+	if (!xa_empty(&f->bindings) &&
+	    xa_find(&f->bindings, &start, end - 1, XA_PRESENT)) {
+		filemap_invalidate_unlock(inode->i_mapping);
+		goto err;
+	}
+
+	/*
+	 * memslots of flag KVM_MEM_GUEST_MEMFD are immutable to change, so
+	 * kvm_gmem_bind() must occur on a new memslot.  Because the memslot
+	 * is not visible yet, kvm_gmem_get_pfn() is guaranteed to see the file.
+	 */
+	WRITE_ONCE(slot->gmem.file, file);
+	slot->gmem.pgoff = start;
+	if (kvm_gmem_supports_mmap(inode))
+		slot->flags |= KVM_MEMSLOT_GMEM_ONLY;
+
+	xa_store_range(&f->bindings, start, end - 1, slot, GFP_KERNEL);
+	filemap_invalidate_unlock(inode->i_mapping);
+
+	/*
+	 * Drop the reference to the file, even on success.  The file pins KVM,
+	 * not the other way 'round.  Active bindings are invalidated if the
+	 * file is closed before memslots are destroyed.
+	 */
+	r = 0;
+err:
+	fput(file);
+	return r;
+}
+
+static void __kvm_gmem_unbind(struct kvm_memory_slot *slot, struct gmem_file *f)
+{
+	unsigned long start = slot->gmem.pgoff;
+	unsigned long end = start + slot->npages;
+
+	xa_store_range(&f->bindings, start, end - 1, NULL, GFP_KERNEL);
+
+	/*
+	 * synchronize_srcu(&kvm->srcu) ensured that kvm_gmem_get_pfn()
+	 * cannot see this memslot.
+	 */
+	WRITE_ONCE(slot->gmem.file, NULL);
+}
+
+void kvm_gmem_unbind(struct kvm_memory_slot *slot)
+{
+	/*
+	 * Nothing to do if the underlying file was _already_ closed, as
+	 * kvm_gmem_release() invalidates and nullifies all bindings.
+	 */
+	if (!slot->gmem.file)
+		return;
+
+	CLASS(gmem_get_file, file)(slot);
+
+	/*
+	 * However, if the file is _being_ closed, then the bindings need to be
+	 * removed as kvm_gmem_release() might not run until after the memslot
+	 * is freed.  Note, modifying the bindings is safe even though the file
+	 * is dying as kvm_gmem_release() nullifies slot->gmem.file under
+	 * slots_lock, and only puts its reference to KVM after destroying all
+	 * bindings.  I.e. reaching this point means kvm_gmem_release() hasn't
+	 * yet destroyed the bindings or freed the gmem_file, and can't do so
+	 * until the caller drops slots_lock.
+	 */
+	if (!file) {
+		__kvm_gmem_unbind(slot, slot->gmem.file->private_data);
+		return;
+	}
+
+	filemap_invalidate_lock(file->f_mapping);
+	__kvm_gmem_unbind(slot, file->private_data);
+	filemap_invalidate_unlock(file->f_mapping);
+}
+
+/* Returns a locked folio on success.  */
+static struct folio *__kvm_gmem_get_pfn(struct file *file,
+					struct kvm_memory_slot *slot,
+					pgoff_t index, kvm_pfn_t *pfn,
+					bool *is_prepared, int *max_order)
+{
+	struct file *slot_file = READ_ONCE(slot->gmem.file);
+	struct gmem_file *f = file->private_data;
+	struct folio *folio;
+
+	if (file != slot_file) {
+		WARN_ON_ONCE(slot_file);
+		return ERR_PTR(-EFAULT);
+	}
+
+	if (xa_load(&f->bindings, index) != slot) {
+		WARN_ON_ONCE(xa_load(&f->bindings, index));
+		return ERR_PTR(-EIO);
+	}
+
+	folio = kvm_gmem_get_folio(file_inode(file), index);
+	if (IS_ERR(folio))
+		return folio;
+
+	if (folio_test_hwpoison(folio)) {
+		folio_unlock(folio);
+		folio_put(folio);
+		return ERR_PTR(-EHWPOISON);
+	}
+
+	*pfn = folio_file_pfn(folio, index);
+	if (max_order)
+		*max_order = 0;
+
+	*is_prepared = folio_test_uptodate(folio);
+	return folio;
+}
+
+int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
+		     gfn_t gfn, kvm_pfn_t *pfn, struct page **page,
+		     int *max_order)
+{
+	pgoff_t index = kvm_gmem_get_index(slot, gfn);
+	struct folio *folio;
+	bool is_prepared = false;
+	int r = 0;
+
+	CLASS(gmem_get_file, file)(slot);
+	if (!file)
+		return -EFAULT;
+
+	folio = __kvm_gmem_get_pfn(file, slot, index, pfn, &is_prepared, max_order);
+	if (IS_ERR(folio))
+		return PTR_ERR(folio);
+
+	if (!is_prepared)
+		r = kvm_gmem_prepare_folio(kvm, slot, gfn, folio);
+
+	folio_unlock(folio);
+
+	if (!r)
+		*page = folio_file_page(folio, index);
+	else
+		folio_put(folio);
+
+	return r;
+}
+EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_gmem_get_pfn);
+
+#ifdef CONFIG_HAVE_KVM_ARCH_GMEM_POPULATE
+long kvm_gmem_populate(struct kvm *kvm, gfn_t start_gfn, void __user *src, long npages,
+		       kvm_gmem_populate_cb post_populate, void *opaque)
+{
+	struct kvm_memory_slot *slot;
+	void __user *p;
+
+	int ret = 0, max_order;
+	long i;
+
+	lockdep_assert_held(&kvm->slots_lock);
+
+	if (WARN_ON_ONCE(npages <= 0))
+		return -EINVAL;
+
+	slot = gfn_to_memslot(kvm, start_gfn);
+	if (!kvm_slot_has_gmem(slot))
+		return -EINVAL;
+
+	CLASS(gmem_get_file, file)(slot);
+	if (!file)
+		return -EFAULT;
+
+	filemap_invalidate_lock(file->f_mapping);
+
+	npages = min_t(ulong, slot->npages - (start_gfn - slot->base_gfn), npages);
+	for (i = 0; i < npages; i += (1 << max_order)) {
+		struct folio *folio;
+		gfn_t gfn = start_gfn + i;
+		pgoff_t index = kvm_gmem_get_index(slot, gfn);
+		bool is_prepared = false;
+		kvm_pfn_t pfn;
+
+		if (signal_pending(current)) {
+			ret = -EINTR;
+			break;
+		}
+
+		folio = __kvm_gmem_get_pfn(file, slot, index, &pfn, &is_prepared, &max_order);
+		if (IS_ERR(folio)) {
+			ret = PTR_ERR(folio);
+			break;
+		}
+
+		if (is_prepared) {
+			folio_unlock(folio);
+			folio_put(folio);
+			ret = -EEXIST;
+			break;
+		}
+
+		folio_unlock(folio);
+		WARN_ON(!IS_ALIGNED(gfn, 1 << max_order) ||
+			(npages - i) < (1 << max_order));
+
+		ret = -EINVAL;
+		while (!kvm_range_has_memory_attributes(kvm, gfn, gfn + (1 << max_order),
+							KVM_MEMORY_ATTRIBUTE_PRIVATE,
+							KVM_MEMORY_ATTRIBUTE_PRIVATE)) {
+			if (!max_order)
+				goto put_folio_and_exit;
+			max_order--;
+		}
+
+		p = src ? src + i * PAGE_SIZE : NULL;
+		ret = post_populate(kvm, gfn, pfn, p, max_order, opaque);
+		if (!ret)
+			kvm_gmem_mark_prepared(folio);
+
+put_folio_and_exit:
+		folio_put(folio);
+		if (ret)
+			break;
+	}
+
+	filemap_invalidate_unlock(file->f_mapping);
+
+	return ret && !i ? ret : i;
+}
+EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_gmem_populate);
+#endif
+
+static struct kmem_cache *kvm_gmem_inode_cachep;
+
+static void kvm_gmem_init_inode_once(void *__gi)
+{
+	struct gmem_inode *gi = __gi;
+
+	/*
+	 * Note!  Don't initialize the inode with anything specific to the
+	 * guest_memfd instance, or that might be specific to how the inode is
+	 * used (from the VFS-layer's perspective).  This hook is called only
+	 * during the initial slab allocation, i.e. only fields/state that are
+	 * idempotent across _all_ use of the inode _object_ can be initialized
+	 * at this time!
+	 */
+	inode_init_once(&gi->vfs_inode);
+}
+
+static struct inode *kvm_gmem_alloc_inode(struct super_block *sb)
+{
+	struct gmem_inode *gi;
+
+	gi = alloc_inode_sb(sb, kvm_gmem_inode_cachep, GFP_KERNEL);
+	if (!gi)
+		return NULL;
+
+	mpol_shared_policy_init(&gi->policy, NULL);
+
+	gi->flags = 0;
+	return &gi->vfs_inode;
+}
+
+static void kvm_gmem_destroy_inode(struct inode *inode)
+{
+	mpol_free_shared_policy(&GMEM_I(inode)->policy);
+}
+
+static void kvm_gmem_free_inode(struct inode *inode)
+{
+	kmem_cache_free(kvm_gmem_inode_cachep, GMEM_I(inode));
+}
+
+static const struct super_operations kvm_gmem_super_operations = {
+	.statfs		= simple_statfs,
+	.alloc_inode	= kvm_gmem_alloc_inode,
+	.destroy_inode	= kvm_gmem_destroy_inode,
+	.free_inode	= kvm_gmem_free_inode,
+};
+
+static int kvm_gmem_init_fs_context(struct fs_context *fc)
+{
+	struct pseudo_fs_context *ctx;
+
+	if (!init_pseudo(fc, GUEST_MEMFD_MAGIC))
+		return -ENOMEM;
+
+	fc->s_iflags |= SB_I_NOEXEC;
+	fc->s_iflags |= SB_I_NODEV;
+	ctx = fc->fs_private;
+	ctx->ops = &kvm_gmem_super_operations;
+
+	return 0;
+}
+
+static struct file_system_type kvm_gmem_fs = {
+	.name		 = "guest_memfd",
+	.init_fs_context = kvm_gmem_init_fs_context,
+	.kill_sb	 = kill_anon_super,
+};
+
+static int kvm_gmem_init_mount(void)
+{
+	kvm_gmem_mnt = kern_mount(&kvm_gmem_fs);
+
+	if (IS_ERR(kvm_gmem_mnt))
+		return PTR_ERR(kvm_gmem_mnt);
+
+	kvm_gmem_mnt->mnt_flags |= MNT_NOEXEC;
+	return 0;
+}
+
+int kvm_gmem_init(struct module *module)
+{
+	struct kmem_cache_args args = {
+		.align = 0,
+		.ctor = kvm_gmem_init_inode_once,
+	};
+	int ret;
+
+	kvm_gmem_fops.owner = module;
+	kvm_gmem_inode_cachep = kmem_cache_create("kvm_gmem_inode_cache",
+						  sizeof(struct gmem_inode),
+						  &args, SLAB_ACCOUNT);
+	if (!kvm_gmem_inode_cachep)
+		return -ENOMEM;
+
+	ret = kvm_gmem_init_mount();
+	if (ret) {
+		kmem_cache_destroy(kvm_gmem_inode_cachep);
+		return ret;
+	}
+	return 0;
+}
+
+void kvm_gmem_exit(void)
+{
+	kern_unmount(kvm_gmem_mnt);
+	kvm_gmem_mnt = NULL;
+	rcu_barrier();
+	kmem_cache_destroy(kvm_gmem_inode_cachep);
+}