diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index 4e2a588465c5..c9624b059eb0 100644
--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -1299,8 +1299,6 @@ static void encode_cap_msg(struct ceph_msg *msg, struct cap_msg_args *arg)
 	 * fscrypt_auth holds the crypto context (if any). fscrypt_file
 	 * tracks the real i_size as an __le64 field (and we use a rounded-up
 	 * i_size in * the traditional size field).
-	 *
-	 * FIXME: should we encrypt fscrypt_file field?
 	 */
 	ceph_encode_32(&p, arg->fscrypt_auth_len);
 	ceph_encode_copy(&p, arg->fscrypt_auth, arg->fscrypt_auth_len);
diff --git a/fs/ceph/file.c b/fs/ceph/file.c
index 1988e75ad4a2..2a780e0133df 100644
--- a/fs/ceph/file.c
+++ b/fs/ceph/file.c
@@ -902,7 +902,8 @@ static inline void fscrypt_adjust_off_and_len(struct inode *inode, u64 *off, u64
  * only return a short read to the caller if we hit EOF.
  */
 ssize_t __ceph_sync_read(struct inode *inode, loff_t *ki_pos,
-			 struct iov_iter *to, int *retry_op)
+			 struct iov_iter *to, int *retry_op,
+			 u64 *assert_ver)
 {
 	struct ceph_inode_info *ci = ceph_inode(inode);
 	struct ceph_fs_client *fsc = ceph_inode_to_client(inode);
@@ -978,6 +979,9 @@ ssize_t __ceph_sync_read(struct inode *inode, loff_t *ki_pos,
 					 req->r_end_latency,
 					 len, ret);
 
+		/* Grab assert version. It must be non-zero. */
+		*assert_ver = req->r_version;
+		WARN_ON_ONCE(assert_ver == 0);
 		ceph_osdc_put_request(req);
 
 		dout("sync_read %llu~%llu got %zd i_size %llu%s\n",
@@ -1074,12 +1078,14 @@ static ssize_t ceph_sync_read(struct kiocb *iocb, struct iov_iter *to,
 {
 	struct file *file = iocb->ki_filp;
 	struct inode *inode = file_inode(file);
+	u64 assert_ver;
 
 	dout("sync_read on file %p %llu~%u %s\n", file, iocb->ki_pos,
 	     (unsigned)iov_iter_count(to),
 	     (file->f_flags & O_DIRECT) ? "O_DIRECT" : "");
 
-	return __ceph_sync_read(inode, &iocb->ki_pos, to, retry_op);
+	return __ceph_sync_read(inode, &iocb->ki_pos, to, retry_op,
+				&assert_ver);
 
 }
 
diff --git a/fs/ceph/inode.c b/fs/ceph/inode.c
index 9b798690fdc9..abb634866897 100644
--- a/fs/ceph/inode.c
+++ b/fs/ceph/inode.c
@@ -21,6 +21,7 @@
 #include "cache.h"
 #include "crypto.h"
 #include <linux/ceph/decode.h>
+#include <linux/ceph/crypto.h>
 
 /*
  * Ceph inode operations
@@ -1034,10 +1035,14 @@ int ceph_fill_inode(struct inode *inode, struct page *locked_page,
 		pool_ns = old_ns;
 
 		if (IS_ENCRYPTED(inode) && size &&
-		    (iinfo->fscrypt_file_len == sizeof(__le64))) {
-			size = __le64_to_cpu(*(__le64 *)iinfo->fscrypt_file);
-			if (info->size != round_up(size, CEPH_FSCRYPT_BLOCK_SIZE))
-				pr_warn("size=%llu fscrypt_file=%llu\n", info->size, size);
+		    (iinfo->fscrypt_file_len >= sizeof(__le64))) {
+			u64 fsize = __le64_to_cpu(*(__le64 *)iinfo->fscrypt_file);
+			if (fsize) {
+				size = fsize;
+				if (info->size != round_up(size, CEPH_FSCRYPT_BLOCK_SIZE))
+					pr_warn("size=%llu fscrypt_file=%llu\n",
+						info->size, size);
+			}
 		}
 
 		queue_trunc = ceph_fill_file_size(inode, issued,
@@ -2229,6 +2234,130 @@ static const struct inode_operations ceph_encrypted_symlink_iops = {
 	.listxattr = ceph_listxattr,
 };
 
+/*
+ * Transfer the encrypted last block to the MDS and the MDS
+ * will update the file when truncating a smaller size.
+ *
+ * We don't support a PAGE_SIZE that is smaller than the
+ * CEPH_FSCRYPT_BLOCK_SIZE.
+ */
+static int fill_fscrypt_truncate(struct inode *inode,
+				 struct ceph_mds_request *req,
+				 struct iattr *attr)
+{
+	struct ceph_inode_info *ci = ceph_inode(inode);
+	int boff = attr->ia_size % CEPH_FSCRYPT_BLOCK_SIZE;
+	loff_t pos, orig_pos = round_down(attr->ia_size, CEPH_FSCRYPT_BLOCK_SIZE);
+	u64 block = orig_pos >> CEPH_FSCRYPT_BLOCK_SHIFT;
+	struct ceph_pagelist *pagelist = NULL;
+	struct kvec iov;
+	struct iov_iter iter;
+	struct page *page = NULL;
+	struct ceph_fscrypt_truncate_size_header header;
+	int retry_op = 0;
+	int len = CEPH_FSCRYPT_BLOCK_SIZE;
+	loff_t i_size = i_size_read(inode);
+	bool fill_header_only = false;
+	u64 assert_ver = cpu_to_le64(0);
+	int got, ret, issued;
+
+	ret = __ceph_get_caps(inode, NULL, CEPH_CAP_FILE_RD, 0, -1, &got);
+	if (ret < 0)
+		return ret;
+
+	dout("%s size %lld -> %lld got cap refs on %s\n", __func__,
+	     i_size, attr->ia_size, ceph_cap_string(got));
+
+	issued = __ceph_caps_issued(ci, NULL);
+
+	/* Try to writeback the dirty pagecaches */
+	if (issued & (CEPH_CAP_FILE_BUFFER))
+		filemap_fdatawrite(&inode->i_data);
+
+	page = __page_cache_alloc(GFP_KERNEL);
+	if (page == NULL) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	iov.iov_base = kmap_local_page(page);
+	iov.iov_len = len;
+	iov_iter_kvec(&iter, READ, &iov, 1, len);
+
+	pos = orig_pos;
+	ret = __ceph_sync_read(inode, &pos, &iter, &retry_op, &assert_ver);
+
+	/*
+	 * If we hit a hole here, we should just skip filling
+	 * the fscrypt for the request, because once the fscrypt
+	 * is enabled, the file will be split into many blocks
+	 * with the size of CEPH_FSCRYPT_BLOCK_SIZE, if there
+	 * has a hole, the hole size should be multiple of block
+	 * size.
+	 */
+	if (pos < i_size && ret < len) {
+		dout("%s hit hole, ppos %lld < size %lld\n",
+		     __func__, pos, i_size);
+
+		ret = 0;
+		fill_header_only = true;
+		goto fill_last_block;
+	}
+
+	/* truncate and zero out the extra contents for the last block */
+	memset(iov.iov_base + boff, 0, PAGE_SIZE - boff);
+
+	/* encrypt the last block */
+	ret = fscrypt_encrypt_block_inplace(inode, page,
+					    CEPH_FSCRYPT_BLOCK_SIZE,
+					    0, block,
+					    GFP_KERNEL);
+	if (ret)
+		goto out;
+
+fill_last_block:
+	pagelist = ceph_pagelist_alloc(GFP_KERNEL);
+	if (!pagelist)
+		return -ENOMEM;
+
+	/* Insert the header first */
+	header.ver = 1;
+	header.compat = 1;
+	if (fill_header_only) {
+		header.data_len = cpu_to_le32(8 + 8 + 4);
+		header.assert_ver = cpu_to_le64(0);
+		header.file_offset = cpu_to_le64(0);
+		header.block_size = cpu_to_le64(0);
+	} else {
+		header.data_len = cpu_to_le32(8 + 8 + 4 + CEPH_FSCRYPT_BLOCK_SIZE);
+		header.assert_ver = assert_ver;
+		header.file_offset = cpu_to_le64(orig_pos);
+		header.block_size = cpu_to_le64(CEPH_FSCRYPT_BLOCK_SIZE);
+	}
+	ret = ceph_pagelist_append(pagelist, &header, sizeof(header));
+	if (ret)
+		goto out;
+
+	if (!fill_header_only) {
+		/* Append the last block contents to pagelist */
+		ret = ceph_pagelist_append(pagelist, iov.iov_base,
+					   CEPH_FSCRYPT_BLOCK_SIZE);
+		if (ret)
+			goto out;
+	}
+	req->r_pagelist = pagelist;
+out:
+	dout("%s %p size dropping cap refs on %s\n", __func__,
+	     inode, ceph_cap_string(got));
+	kunmap_local(iov.iov_base);
+	if (page)
+		__free_pages(page, 0);
+	if (ret && pagelist)
+		ceph_pagelist_release(pagelist);
+	ceph_put_cap_refs(ci, got);
+	return ret;
+}
+
 int __ceph_setattr(struct inode *inode, struct iattr *attr, struct ceph_iattr *cia)
 {
 	struct ceph_inode_info *ci = ceph_inode(inode);
@@ -2236,12 +2365,14 @@ int __ceph_setattr(struct inode *inode, struct iattr *attr, struct ceph_iattr *c
 	struct ceph_mds_request *req;
 	struct ceph_mds_client *mdsc = ceph_sb_to_client(inode->i_sb)->mdsc;
 	struct ceph_cap_flush *prealloc_cf;
+	loff_t isize = i_size_read(inode);
 	int issued;
 	int release = 0, dirtied = 0;
 	int mask = 0;
 	int err = 0;
 	int inode_dirty_flags = 0;
 	bool lock_snap_rwsem = false;
+	bool fill_fscrypt;
 
 	prealloc_cf = ceph_alloc_cap_flush();
 	if (!prealloc_cf)
@@ -2254,6 +2385,8 @@ int __ceph_setattr(struct inode *inode, struct iattr *attr, struct ceph_iattr *c
 		return PTR_ERR(req);
 	}
 
+retry:
+	fill_fscrypt = false;
 	spin_lock(&ci->i_ceph_lock);
 	issued = __ceph_caps_issued(ci, NULL);
 
@@ -2367,10 +2500,27 @@ int __ceph_setattr(struct inode *inode, struct iattr *attr, struct ceph_iattr *c
 		}
 	}
 	if (ia_valid & ATTR_SIZE) {
-		loff_t isize = i_size_read(inode);
-
 		dout("setattr %p size %lld -> %lld\n", inode, isize, attr->ia_size);
-		if ((issued & CEPH_CAP_FILE_EXCL) && attr->ia_size >= isize) {
+		/*
+		 * Only when the new size is smaller and not aligned to
+		 * CEPH_FSCRYPT_BLOCK_SIZE will the RMW is needed.
+		 */
+		if (IS_ENCRYPTED(inode) && attr->ia_size < isize &&
+		    (attr->ia_size % CEPH_FSCRYPT_BLOCK_SIZE)) {
+			mask |= CEPH_SETATTR_SIZE;
+			release |= CEPH_CAP_FILE_SHARED | CEPH_CAP_FILE_EXCL |
+				   CEPH_CAP_FILE_RD | CEPH_CAP_FILE_WR;
+			set_bit(CEPH_MDS_R_FSCRYPT_FILE, &req->r_req_flags);
+			mask |= CEPH_SETATTR_FSCRYPT_FILE;
+			req->r_args.setattr.size =
+				cpu_to_le64(round_up(attr->ia_size,
+						     CEPH_FSCRYPT_BLOCK_SIZE));
+			req->r_args.setattr.old_size =
+				cpu_to_le64(round_up(isize,
+						     CEPH_FSCRYPT_BLOCK_SIZE));
+			req->r_fscrypt_file = attr->ia_size;
+			fill_fscrypt = true;
+		} else if ((issued & CEPH_CAP_FILE_EXCL) && attr->ia_size >= isize) {
 			if (attr->ia_size > isize) {
 				i_size_write(inode, attr->ia_size);
 				inode->i_blocks = calc_inode_blocks(attr->ia_size);
@@ -2393,7 +2543,6 @@ int __ceph_setattr(struct inode *inode, struct iattr *attr, struct ceph_iattr *c
 					cpu_to_le64(round_up(isize,
 							     CEPH_FSCRYPT_BLOCK_SIZE));
 				req->r_fscrypt_file = attr->ia_size;
-				/* FIXME: client must zero out any partial blocks! */
 			} else {
 				req->r_args.setattr.size = cpu_to_le64(attr->ia_size);
 				req->r_args.setattr.old_size = cpu_to_le64(isize);
@@ -2465,7 +2614,6 @@ int __ceph_setattr(struct inode *inode, struct iattr *attr, struct ceph_iattr *c
 	if (inode_dirty_flags)
 		__mark_inode_dirty(inode, inode_dirty_flags);
 
-
 	if (mask) {
 		req->r_inode = inode;
 		ihold(inode);
@@ -2473,7 +2621,23 @@ int __ceph_setattr(struct inode *inode, struct iattr *attr, struct ceph_iattr *c
 		req->r_args.setattr.mask = cpu_to_le32(mask);
 		req->r_num_caps = 1;
 		req->r_stamp = attr->ia_ctime;
+		if (fill_fscrypt) {
+			err = fill_fscrypt_truncate(inode, req, attr);
+			if (err)
+				goto out;
+		}
+
+		/*
+		 * The truncate will return -EAGAIN when some one
+		 * has updated the last block before the MDS hold
+		 * the xlock for the FILE lock. Need to retry it.
+		 */
 		err = ceph_mdsc_do_request(mdsc, NULL, req);
+		if (err == -EAGAIN) {
+			dout("setattr %p result=%d (%s locally, %d remote), retry it!\n",
+			     inode, err, ceph_cap_string(dirtied), mask);
+			goto retry;
+		}
 	}
 out:
 	dout("setattr %p result=%d (%s locally, %d remote)\n", inode, err,
diff --git a/fs/ceph/super.h b/fs/ceph/super.h
index 57bc952c54e1..c8144273ff28 100644
--- a/fs/ceph/super.h
+++ b/fs/ceph/super.h
@@ -1236,7 +1236,8 @@ extern int ceph_open(struct inode *inode, struct file *file);
 extern int ceph_atomic_open(struct inode *dir, struct dentry *dentry,
 			    struct file *file, unsigned flags, umode_t mode);
 extern ssize_t __ceph_sync_read(struct inode *inode, loff_t *ki_pos,
-				struct iov_iter *to, int *retry_op);
+				struct iov_iter *to, int *retry_op,
+				u64 *assert_ver);
 extern int ceph_release(struct inode *inode, struct file *filp);
 extern void ceph_fill_inline_data(struct inode *inode, struct page *locked_page,
 				  char *data, size_t len);
diff --git a/include/linux/ceph/crypto.h b/include/linux/ceph/crypto.h
new file mode 100644
index 000000000000..e0f799d4d4ee
--- /dev/null
+++ b/include/linux/ceph/crypto.h
@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _FS_CEPH_CRYPTO_H
+#define _FS_CEPH_CRYPTO_H
+
+#include <linux/types.h>
+
+/*
+ * Header for the crypted file when truncating the size, this
+ * will be sent to MDS, and MDS will do the encrypted last
+ * block's update and size truncating.
+ */
+struct ceph_fscrypt_truncate_size_header {
+       __u8  ver;
+       __u8  compat;
+       /* length of sizeof(assert_ver + file_offset + block_size + CEPH_FSCRYPT_BLOCK_SIZE) */
+       __le32 data_len;
+
+       __le64 assert_ver;
+       __le64 file_offset;
+       __le32 block_size;
+} __packed;
+
+#endif
