linux-kernel - [ 108/173] target/file: Fix 32-bit highmem breakage for SGL -> iovec mapping

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Message-Id: <20121228190352.897309171@decadent.org.uk>
Date:	Fri, 28 Dec 2012 20:05:18 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Nicholas Bellinger <nab@...ux-iscsi.org>
Subject: [ 108/173] target/file: Fix 32-bit highmem breakage for SGL -> iovec mapping

3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

commit 40ff2c3b3da35dd3a00ac6722056a59b4b3f2caf upstream.

This patch changes vectored file I/O to use kmap + kunmap when mapping
incoming SGL memory -> struct iovec in order to properly support 32-bit
highmem configurations.  This is because an extra bounce buffer may be
required when processing scatterlist pages allocated with GFP_KERNEL.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Signed-off-by: Nicholas Bellinger <nab@...ux-iscsi.org>
[bwh: Backported to 3.2: use task->task_sg{,_nents} for iteration]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/target/target_core_file.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

--- a/drivers/target/target_core_file.c
+++ b/drivers/target/target_core_file.c
@@ -300,7 +300,7 @@ static int fd_do_readv(struct se_task *t
 
 	for_each_sg(task->task_sg, sg, task->task_sg_nents, i) {
 		iov[i].iov_len = sg->length;
-		iov[i].iov_base = sg_virt(sg);
+		iov[i].iov_base = kmap(sg_page(sg)) + sg->offset;
 	}
 
 	old_fs = get_fs();
@@ -308,6 +308,8 @@ static int fd_do_readv(struct se_task *t
 	ret = vfs_readv(fd, &iov[0], task->task_sg_nents, &pos);
 	set_fs(old_fs);
 
+	for_each_sg(task->task_sg, sg, task->task_sg_nents, i)
+		kunmap(sg_page(sg));
 	kfree(iov);
 	/*
 	 * Return zeros and GOOD status even if the READ did not return
@@ -353,7 +355,7 @@ static int fd_do_writev(struct se_task *
 
 	for_each_sg(task->task_sg, sg, task->task_sg_nents, i) {
 		iov[i].iov_len = sg->length;
-		iov[i].iov_base = sg_virt(sg);
+		iov[i].iov_base = kmap(sg_page(sg)) + sg->offset;
 	}
 
 	old_fs = get_fs();
@@ -361,6 +363,9 @@ static int fd_do_writev(struct se_task *
 	ret = vfs_writev(fd, &iov[0], task->task_sg_nents, &pos);
 	set_fs(old_fs);
 
+	for_each_sg(task->task_sg, sg, task->task_sg_nents, i)
+		kunmap(sg_page(sg));
+
 	kfree(iov);
 
 	if (ret < 0 || ret != task->task_size) {


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