+ hfs-replace-kmap-with-kmap_local_page-in-bnodec.patch added to mm-nonmm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: hfs: replace kmap() with kmap_local_page() in bnode.c
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     hfs-replace-kmap-with-kmap_local_page-in-bnodec.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/hfs-replace-kmap-with-kmap_local_page-in-bnodec.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: "Fabio M. De Francesco" <fmdefrancesco@gmail.com>
Subject: hfs: replace kmap() with kmap_local_page() in bnode.c
Date: Sun, 21 Aug 2022 20:03:59 +0200

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.

Link: https://lkml.kernel.org/r/20220821180400.8198-3-fmdefrancesco@gmail.com
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Suggested-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Viacheslav Dubeyko <slava@dubeyko.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Chaitanya Kulkarni <kch@nvidia.com>
Cc: Christian Brauner (Microsoft) <brauner@kernel.org>
Cc: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Cc: Jeff Layton <jlayton@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Kees Cook <keescook@chromium.org>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/hfs/bnode.c |   32 ++++++++++++--------------------
 1 file changed, 12 insertions(+), 20 deletions(-)

--- a/fs/hfs/bnode.c~hfs-replace-kmap-with-kmap_local_page-in-bnodec
+++ a/fs/hfs/bnode.c
@@ -21,7 +21,6 @@ void hfs_bnode_read(struct hfs_bnode *no
 	int pagenum;
 	int bytes_read;
 	int bytes_to_read;
-	void *vaddr;
 
 	off += node->page_offset;
 	pagenum = off >> PAGE_SHIFT;
@@ -33,9 +32,7 @@ void hfs_bnode_read(struct hfs_bnode *no
 		page = node->page[pagenum];
 		bytes_to_read = min_t(int, len - bytes_read, PAGE_SIZE - off);
 
-		vaddr = kmap_atomic(page);
-		memcpy(buf + bytes_read, vaddr + off, bytes_to_read);
-		kunmap_atomic(vaddr);
+		memcpy_from_page(buf + bytes_read, page, off, bytes_to_read);
 
 		pagenum++;
 		off = 0; /* page offset only applies to the first page */
@@ -80,8 +77,7 @@ void hfs_bnode_write(struct hfs_bnode *n
 	off += node->page_offset;
 	page = node->page[0];
 
-	memcpy(kmap(page) + off, buf, len);
-	kunmap(page);
+	memcpy_to_page(page, off, buf, len);
 	set_page_dirty(page);
 }
 
@@ -105,8 +101,7 @@ void hfs_bnode_clear(struct hfs_bnode *n
 	off += node->page_offset;
 	page = node->page[0];
 
-	memset(kmap(page) + off, 0, len);
-	kunmap(page);
+	memzero_page(page, off, len);
 	set_page_dirty(page);
 }
 
@@ -123,9 +118,7 @@ void hfs_bnode_copy(struct hfs_bnode *ds
 	src_page = src_node->page[0];
 	dst_page = dst_node->page[0];
 
-	memcpy(kmap(dst_page) + dst, kmap(src_page) + src, len);
-	kunmap(src_page);
-	kunmap(dst_page);
+	memcpy_page(dst_page, dst, src_page, src, len);
 	set_page_dirty(dst_page);
 }
 
@@ -140,9 +133,9 @@ void hfs_bnode_move(struct hfs_bnode *no
 	src += node->page_offset;
 	dst += node->page_offset;
 	page = node->page[0];
-	ptr = kmap(page);
+	ptr = kmap_local_page(page);
 	memmove(ptr + dst, ptr + src, len);
-	kunmap(page);
+	kunmap_local(ptr);
 	set_page_dirty(page);
 }
 
@@ -346,13 +339,14 @@ struct hfs_bnode *hfs_bnode_find(struct
 	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:
@@ -436,14 +430,12 @@ struct hfs_bnode *hfs_bnode_create(struc
 	}
 
 	pagep = node->page;
-	memset(kmap(*pagep) + node->page_offset, 0,
-	       min((int)PAGE_SIZE, (int)tree->node_size));
+	memzero_page(*pagep, node->page_offset,
+		     min((int)PAGE_SIZE, (int)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);
_

Patches currently in -mm which might be from fmdefrancesco@gmail.com are

hfsplus-unmap-the-page-in-the-fail_page-label.patch
hfsplus-convert-kmap-to-kmap_local_page-in-bnodec.patch
hfsplus-convert-kmap-to-kmap_local_page-in-bitmapc.patch
hfsplus-convert-kmap-to-kmap_local_page-in-btreec.patch
fs-isofs-replace-kmap-with-kmap_local_page.patch
kexec-replace-kmap-with-kmap_local_page.patch
hfs-unmap-the-page-in-the-fail_page-label.patch
hfs-replace-kmap-with-kmap_local_page-in-bnodec.patch
hfs-replace-kmap-with-kmap_local_page-in-btreec.patch