mm: vmalloc: convert vread() to vread_iter()

Having previously laid the foundation for converting vread() to an
iterator function, pull the trigger and do so.

This patch attempts to provide minimal refactoring and to reflect the
existing logic as best we can, for example we continue to zero portions of
memory not read, as before.

Overall, there should be no functional difference other than a performance
improvement in /proc/kcore access to vmalloc regions.

Now we have eliminated the need for a bounce buffer in read_kcore_iter(),
we dispense with it, and try to write to user memory optimistically but
with faults disabled via copy_page_to_iter_nofault().  We already have
preemption disabled by holding a spin lock.  We continue faulting in until
the operation is complete.

Additionally, we must account for the fact that at any point a copy may
fail (most likely due to a fault not being able to occur), we exit
indicating fewer bytes retrieved than expected.

[sfr@canb.auug.org.au: fix sparc64 warning]
  Link: https://lkml.kernel.org/r/20230320144721.663280c3@canb.auug.org.au
[lstoakes@gmail.com: redo Stephen's sparc build fix]
  Link: https://lkml.kernel.org/r/8506cbc667c39205e65a323f750ff9c11a463798.1679566220.git.lstoakes@gmail.com
[akpm@linux-foundation.org: unbreak uio.h includes]
Link: https://lkml.kernel.org/r/941f88bc5ab928e6656e1e2593b91bf0f8c81e1b.1679511146.git.lstoakes@gmail.com
Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Reviewed-by: Baoquan He <bhe@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Liu Shixin <liushixin2@huawei.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 23 insertions, 21 deletions

diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
index 08b795fd80b4..25b44b303b35 100644
--- a/fs/proc/kcore.c
+++ b/fs/proc/kcore.c
@@ -307,13 +307,9 @@ static void append_kcore_note(char *notes, size_t *i, const char *name,
 	*i = ALIGN(*i + descsz, 4);
 }
 
-static ssize_t
-read_kcore_iter(struct kiocb *iocb, struct iov_iter *iter)
+static ssize_t read_kcore_iter(struct kiocb *iocb, struct iov_iter *iter)
 {
-	struct file *file = iocb->ki_filp;
-	char *buf = file->private_data;
 	loff_t *fpos = &iocb->ki_pos;
-
 	size_t phdrs_offset, notes_offset, data_offset;
 	size_t page_offline_frozen = 1;
 	size_t phdrs_len, notes_len;
@@ -507,13 +503,30 @@ read_kcore_iter(struct kiocb *iocb, struct iov_iter *iter)
 
 		switch (m->type) {
 		case KCORE_VMALLOC:
-			vread(buf, (char *)start, tsz);
-			/* we have to zero-fill user buffer even if no read */
-			if (copy_to_iter(buf, tsz, iter) != tsz) {
-				ret = -EFAULT;
-				goto out;
+		{
+			const char *src = (char *)start;
+			size_t read = 0, left = tsz;
+
+			/*
+			 * vmalloc uses spinlocks, so we optimistically try to
+			 * read memory. If this fails, fault pages in and try
+			 * again until we are done.
+			 */
+			while (true) {
+				read += vread_iter(iter, src, left);
+				if (read == tsz)
+					break;
+
+				src += read;
+				left -= read;
+
+				if (fault_in_iov_iter_writeable(iter, left)) {
+					ret = -EFAULT;
+					goto out;
+				}
 			}
 			break;
+		}
 		case KCORE_USER:
 			/* User page is handled prior to normal kernel page: */
 			if (copy_to_iter((char *)start, tsz, iter) != tsz) {
@@ -582,10 +595,6 @@ static int open_kcore(struct inode *inode, struct file *filp)
 	if (ret)
 		return ret;
 
-	filp->private_data = kmalloc(PAGE_SIZE, GFP_KERNEL);
-	if (!filp->private_data)
-		return -ENOMEM;
-
 	if (kcore_need_update)
 		kcore_update_ram();
 	if (i_size_read(inode) != proc_root_kcore->size) {
@@ -596,16 +605,9 @@ static int open_kcore(struct inode *inode, struct file *filp)
 	return 0;
 }
 
-static int release_kcore(struct inode *inode, struct file *file)
-{
-	kfree(file->private_data);
-	return 0;
-}
-
 static const struct proc_ops kcore_proc_ops = {
 	.proc_read_iter	= read_kcore_iter,
 	.proc_open	= open_kcore,
-	.proc_release	= release_kcore,
 	.proc_lseek	= default_llseek,
 };