Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   "Fabio M. De Francesco" <fmdefrancesco@gmail.com>
To:     "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        "Fabio M. De Francesco" <fmdefrancesco@gmail.com>,
        Ira Weiny <ira.weiny@intel.com>, Jens Axboe <axboe@kernel.dk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Bart Van Assche <bvanassche@acm.org>,
        Kees Cook <keescook@chromium.org>,
        Muchun Song <songmuchun@bytedance.com>,
        Viacheslav Dubeyko <slava@dubeyko.com>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH 2/4] hfsplus: Convert kmap() to kmap_local_page() in bnode.c
Date:   Tue,  9 Aug 2022 22:31:03 +0200
Message-Id: <20220809203105.26183-3-fmdefrancesco@gmail.com>
In-Reply-To: <20220809203105.26183-1-fmdefrancesco@gmail.com>
References: <20220809203105.26183-1-fmdefrancesco@gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Precedence: bulk

kmap() is being deprecated in favor of kmap_local_page().

Two main problems with kmap(): (1) It comes with an overhead as mapping
space is restricted and protected by a global lock for synchronization and
(2) it also requires global TLB invalidation when the kmap’s pool wraps
and it might block when the mapping space is fully utilized until a slot
becomes available.

With kmap_local_page() the mappings are per thread, CPU local, can take
page faults, and can be called from any context (including interrupts).
It is faster than kmap() in kernels with HIGHMEM enabled. Furthermore,
the tasks can be preempted and, when they are scheduled to run again, the
kernel virtual addresses are restored and still valid.

Since its use in bnode.c is safe everywhere, it should be preferred.

Therefore, replace kmap() with kmap_local_page() in bnode.c. Where
possible, use the suited standard helpers (memzero_page(), memcpy_page())
instead of open coding kmap_local_page() plus memset() or memcpy().

Tested in a QEMU/KVM x86_32 VM, 6GB RAM, booting a kernel with
HIGHMEM64GB enabled.

Cc: Viacheslav Dubeyko <slava@dubeyko.com>
Suggested-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
---
 fs/hfsplus/bnode.c | 105 +++++++++++++++++++++------------------------
 1 file changed, 48 insertions(+), 57 deletions(-)

diff --git a/fs/hfsplus/bnode.c b/fs/hfsplus/bnode.c
index a5ab00e54220..87974d5e6791 100644
--- a/fs/hfsplus/bnode.c
+++ b/fs/hfsplus/bnode.c
@@ -29,14 +29,12 @@ void hfs_bnode_read(struct hfs_bnode *node, void *buf, int off, int len)
 	off &= ~PAGE_MASK;
 
 	l = min_t(int, len, PAGE_SIZE - off);
-	memcpy(buf, kmap(*pagep) + off, l);
-	kunmap(*pagep);
+	memcpy_from_page(buf, *pagep, off, l);
 
 	while ((len -= l) != 0) {
 		buf += l;
 		l = min_t(int, len, PAGE_SIZE);
-		memcpy(buf, kmap(*++pagep), l);
-		kunmap(*pagep);
+		memcpy_from_page(buf, *++pagep, 0, l);
 	}
 }
 
@@ -82,16 +80,14 @@ void hfs_bnode_write(struct hfs_bnode *node, void *buf, int off, int len)
 	off &= ~PAGE_MASK;
 
 	l = min_t(int, len, PAGE_SIZE - off);
-	memcpy(kmap(*pagep) + off, buf, l);
+	memcpy_to_page(*pagep, off, buf, l);
 	set_page_dirty(*pagep);
-	kunmap(*pagep);
 
 	while ((len -= l) != 0) {
 		buf += l;
 		l = min_t(int, len, PAGE_SIZE);
-		memcpy(kmap(*++pagep), buf, l);
+		memcpy_to_page(*++pagep, 0, buf, l);
 		set_page_dirty(*pagep);
-		kunmap(*pagep);
 	}
 }
 
@@ -112,15 +108,13 @@ void hfs_bnode_clear(struct hfs_bnode *node, int off, int len)
 	off &= ~PAGE_MASK;
 
 	l = min_t(int, len, PAGE_SIZE - off);
-	memset(kmap(*pagep) + off, 0, l);
+	memzero_page(*pagep, off, l);
 	set_page_dirty(*pagep);
-	kunmap(*pagep);
 
 	while ((len -= l) != 0) {
 		l = min_t(int, len, PAGE_SIZE);
-		memset(kmap(*++pagep), 0, l);
+		memzero_page(*++pagep, 0, l);
 		set_page_dirty(*pagep);
-		kunmap(*pagep);
 	}
 }
 
@@ -142,24 +136,20 @@ void hfs_bnode_copy(struct hfs_bnode *dst_node, int dst,
 
 	if (src == dst) {
 		l = min_t(int, len, PAGE_SIZE - src);
-		memcpy(kmap(*dst_page) + src, kmap(*src_page) + src, l);
-		kunmap(*src_page);
+		memcpy_page(*dst_page, src, *src_page, src, l);
 		set_page_dirty(*dst_page);
-		kunmap(*dst_page);
 
 		while ((len -= l) != 0) {
 			l = min_t(int, len, PAGE_SIZE);
-			memcpy(kmap(*++dst_page), kmap(*++src_page), l);
-			kunmap(*src_page);
+			memcpy_page(*++dst_page, 0, *++src_page, 0, l);
 			set_page_dirty(*dst_page);
-			kunmap(*dst_page);
 		}
 	} else {
 		void *src_ptr, *dst_ptr;
 
 		do {
-			src_ptr = kmap(*src_page) + src;
-			dst_ptr = kmap(*dst_page) + dst;
+			dst_ptr = kmap_local_page(*dst_page) + dst;
+			src_ptr = kmap_local_page(*src_page) + src;
 			if (PAGE_SIZE - src < PAGE_SIZE - dst) {
 				l = PAGE_SIZE - src;
 				src = 0;
@@ -171,9 +161,9 @@ void hfs_bnode_copy(struct hfs_bnode *dst_node, int dst,
 			}
 			l = min(len, l);
 			memcpy(dst_ptr, src_ptr, l);
-			kunmap(*src_page);
+			kunmap_local(src_ptr);
 			set_page_dirty(*dst_page);
-			kunmap(*dst_page);
+			kunmap_local(dst_ptr);
 			if (!dst)
 				dst_page++;
 			else
@@ -185,6 +175,7 @@ void hfs_bnode_copy(struct hfs_bnode *dst_node, int dst,
 void hfs_bnode_move(struct hfs_bnode *node, int dst, int src, int len)
 {
 	struct page **src_page, **dst_page;
+	void *src_ptr, *dst_ptr;
 	int l;
 
 	hfs_dbg(BNODE_MOD, "movebytes: %u,%u,%u\n", dst, src, len);
@@ -202,27 +193,28 @@ void hfs_bnode_move(struct hfs_bnode *node, int dst, int src, int len)
 
 		if (src == dst) {
 			while (src < len) {
-				memmove(kmap(*dst_page), kmap(*src_page), src);
-				kunmap(*src_page);
+				dst_ptr = kmap_local_page(*dst_page);
+				src_ptr = kmap_local_page(*src_page);
+				memmove(dst_ptr, src_ptr, src);
+				kunmap_local(src_ptr);
 				set_page_dirty(*dst_page);
-				kunmap(*dst_page);
+				kunmap_local(dst_ptr);
 				len -= src;
 				src = PAGE_SIZE;
 				src_page--;
 				dst_page--;
 			}
 			src -= len;
-			memmove(kmap(*dst_page) + src,
-				kmap(*src_page) + src, len);
-			kunmap(*src_page);
+			dst_ptr = kmap_local_page(*dst_page);
+			src_ptr = kmap_local_page(*src_page);
+			memmove(dst_ptr + src, src_ptr + src, len);
+			kunmap_local(src_ptr);
 			set_page_dirty(*dst_page);
-			kunmap(*dst_page);
+			kunmap_local(dst_ptr);
 		} else {
-			void *src_ptr, *dst_ptr;
-
 			do {
-				src_ptr = kmap(*src_page) + src;
-				dst_ptr = kmap(*dst_page) + dst;
+				dst_ptr = kmap_local_page(*dst_page) + dst;
+				src_ptr = kmap_local_page(*src_page) + src;
 				if (src < dst) {
 					l = src;
 					src = PAGE_SIZE;
@@ -234,9 +226,9 @@ void hfs_bnode_move(struct hfs_bnode *node, int dst, int src, int len)
 				}
 				l = min(len, l);
 				memmove(dst_ptr - l, src_ptr - l, l);
-				kunmap(*src_page);
+				kunmap_local(src_ptr);
 				set_page_dirty(*dst_page);
-				kunmap(*dst_page);
+				kunmap_local(dst_ptr);
 				if (dst == PAGE_SIZE)
 					dst_page--;
 				else
@@ -251,26 +243,27 @@ void hfs_bnode_move(struct hfs_bnode *node, int dst, int src, int len)
 
 		if (src == dst) {
 			l = min_t(int, len, PAGE_SIZE - src);
-			memmove(kmap(*dst_page) + src,
-				kmap(*src_page) + src, l);
-			kunmap(*src_page);
+
+			dst_ptr = kmap_local_page(*dst_page) + src;
+			src_ptr = kmap_local_page(*src_page) + src;
+			memmove(dst_ptr, src_ptr, l);
+			kunmap_local(src_ptr);
 			set_page_dirty(*dst_page);
-			kunmap(*dst_page);
+			kunmap_local(dst_ptr);
 
 			while ((len -= l) != 0) {
 				l = min_t(int, len, PAGE_SIZE);
-				memmove(kmap(*++dst_page),
-					kmap(*++src_page), l);
-				kunmap(*src_page);
+				dst_ptr = kmap_local_page(*++dst_page);
+				src_ptr = kmap_local_page(*++src_page);
+				memmove(dst_ptr, src_ptr, l);
+				kunmap_local(src_ptr);
 				set_page_dirty(*dst_page);
-				kunmap(*dst_page);
+				kunmap_local(dst_ptr);
 			}
 		} else {
-			void *src_ptr, *dst_ptr;
-
 			do {
-				src_ptr = kmap(*src_page) + src;
-				dst_ptr = kmap(*dst_page) + dst;
+				dst_ptr = kmap_local_page(*dst_page) + dst;
+				src_ptr = kmap_local_page(*src_page) + src;
 				if (PAGE_SIZE - src <
 						PAGE_SIZE - dst) {
 					l = PAGE_SIZE - src;
@@ -283,9 +276,9 @@ void hfs_bnode_move(struct hfs_bnode *node, int dst, int src, int len)
 				}
 				l = min(len, l);
 				memmove(dst_ptr, src_ptr, l);
-				kunmap(*src_page);
+				kunmap_local(src_ptr);
 				set_page_dirty(*dst_page);
-				kunmap(*dst_page);
+				kunmap_local(dst_ptr);
 				if (!dst)
 					dst_page++;
 				else
@@ -498,14 +491,14 @@ struct hfs_bnode *hfs_bnode_find(struct hfs_btree *tree, u32 num)
 	if (!test_bit(HFS_BNODE_NEW, &node->flags))
 		return node;
 
-	desc = (struct hfs_bnode_desc *)(kmap(node->page[0]) +
-			node->page_offset);
+	desc = (struct hfs_bnode_desc *)(kmap_local_page(node->page[0]) +
+							 node->page_offset);
 	node->prev = be32_to_cpu(desc->prev);
 	node->next = be32_to_cpu(desc->next);
 	node->num_recs = be16_to_cpu(desc->num_recs);
 	node->type = desc->type;
 	node->height = desc->height;
-	kunmap(node->page[0]);
+	kunmap_local(desc);
 
 	switch (node->type) {
 	case HFS_NODE_HEADER:
@@ -589,14 +582,12 @@ struct hfs_bnode *hfs_bnode_create(struct hfs_btree *tree, u32 num)
 	}
 
 	pagep = node->page;
-	memset(kmap(*pagep) + node->page_offset, 0,
-	       min_t(int, PAGE_SIZE, tree->node_size));
+	memzero_page(*pagep, node->page_offset,
+		     min_t(int, PAGE_SIZE, tree->node_size));
 	set_page_dirty(*pagep);
-	kunmap(*pagep);
 	for (i = 1; i < tree->pages_per_bnode; i++) {
-		memset(kmap(*++pagep), 0, PAGE_SIZE);
+		memzero_page(*++pagep, 0, PAGE_SIZE);
 		set_page_dirty(*pagep);
-		kunmap(*pagep);
 	}
 	clear_bit(HFS_BNODE_NEW, &node->flags);
 	wake_up(&node->lock_wq);
-- 
2.37.1