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From: Christian Schoenebeck <linux_oss@crudebyte.com>
To: v9fs-developer@lists.sourceforge.net
Cc: netdev@vger.kernel.org,
	Dominique Martinet <asmadeus@codewreck.org>,
	Eric Van Hensbergen <ericvh@gmail.com>,
	Latchesar Ionkov <lucho@ionkov.net>, Greg Kurz <groug@kaod.org>,
	Vivek Goyal <vgoyal@redhat.com>
Subject: [PATCH v3 7/7] 9p/trans_virtio: resize sg lists to whatever is possible
Date: Wed, 22 Sep 2021 18:00:35 +0200	[thread overview]
Message-ID: <3a0d9c26581f237976c5903e332d49c9727b3fa7.1632327421.git.linux_oss@crudebyte.com> (raw)
In-Reply-To: <cover.1632327421.git.linux_oss@crudebyte.com>

Right now vq_sg_resize() used a lazy implementation following
the all-or-nothing princible. So it either resized exactly to
the requested new amount of sg lists, or it did not resize at
all.

The problem with this is if a user supplies a very large msize
value, resize would simply fail and the user would stick to
the default maximum msize supported by the virtio transport.

To resolve this potential issue, change vq_sg_resize() to resize
the passed sg list to whatever is possible on the machine.

Signed-off-by: Christian Schoenebeck <linux_oss@crudebyte.com>
---
 net/9p/trans_virtio.c | 68 ++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 60 insertions(+), 8 deletions(-)

diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
index 147ebf647a95..4c61b4857bea 100644
--- a/net/9p/trans_virtio.c
+++ b/net/9p/trans_virtio.c
@@ -208,24 +208,67 @@ static struct virtqueue_sg *vq_sg_alloc(unsigned int nsgl)
  * amount of lists
  * @_vq_sg: scatter/gather lists to be resized
  * @nsgl: new amount of scatter/gather lists
+ *
+ * Old scatter/gather lists are retained. Only growing the size is supported.
+ * If the requested amount cannot be satisfied, then lists are increased to
+ * whatever is possible.
  */
 static int vq_sg_resize(struct virtqueue_sg **_vq_sg, unsigned int nsgl)
 {
 	struct virtqueue_sg *vq_sg;
+	unsigned int i;
+	size_t sz;
+	int ret = 0;
 
 	BUG_ON(!_vq_sg || !nsgl);
 	vq_sg = *_vq_sg;
+	if (nsgl > VIRTQUEUE_SG_NSGL_MAX)
+		nsgl = VIRTQUEUE_SG_NSGL_MAX;
 	if (vq_sg->nsgl == nsgl)
 		return 0;
+	if (vq_sg->nsgl > nsgl)
+		return -ENOTSUPP;
+
+	vq_sg = kzalloc(sizeof(struct virtqueue_sg) +
+			nsgl * sizeof(struct scatterlist *),
+			GFP_KERNEL);
 
-	/* lazy resize implementation for now */
-	vq_sg = vq_sg_alloc(nsgl);
 	if (!vq_sg)
 		return -ENOMEM;
 
+	/* copy over old scatter gather lists */
+	sz = sizeof(struct virtqueue_sg) +
+		(*_vq_sg)->nsgl * sizeof(struct scatterlist *);
+	memcpy(vq_sg, *_vq_sg, sz);
+
+	vq_sg->nsgl = nsgl;
+
+	for (i = (*_vq_sg)->nsgl; i < nsgl; ++i) {
+		vq_sg->sgl[i] = kmalloc_array(
+			SG_MAX_SINGLE_ALLOC, sizeof(struct scatterlist),
+			GFP_KERNEL
+		);
+		/*
+		 * handle failed allocation as soft error, we take whatever
+		 * we get
+		 */
+		if (!vq_sg->sgl[i]) {
+			ret = -ENOMEM;
+			vq_sg->nsgl = nsgl = i;
+			break;
+		}
+		sg_init_table(vq_sg->sgl[i], SG_MAX_SINGLE_ALLOC);
+		if (i) {
+			/* chain the lists */
+			sg_chain(vq_sg->sgl[i - 1], SG_MAX_SINGLE_ALLOC,
+				 vq_sg->sgl[i]);
+		}
+	}
+	sg_mark_end(&vq_sg->sgl[nsgl - 1][SG_MAX_SINGLE_ALLOC - 1]);
+
 	kfree(*_vq_sg);
 	*_vq_sg = vq_sg;
-	return 0;
+	return ret;
 }
 
 /**
@@ -846,12 +889,21 @@ p9_virtio_create(struct p9_client *client, const char *devname, char *args)
 		if (nsgl > chan->vq_sg->nsgl) {
 			/*
 			 * if resize fails, no big deal, then just
-			 * continue with default msize instead
+			 * continue with whatever we got
+			 */
+			vq_sg_resize(&chan->vq_sg, nsgl);
+			/*
+			 * actual allocation size might be less than
+			 * requested, so use vq_sg->nsgl instead of nsgl
 			 */
-			if (!vq_sg_resize(&chan->vq_sg, nsgl)) {
-				client->trans_maxsize =
-					PAGE_SIZE *
-					((nsgl * SG_USER_PAGES_PER_LIST) - 3);
+			client->trans_maxsize =
+				PAGE_SIZE * ((chan->vq_sg->nsgl *
+				SG_USER_PAGES_PER_LIST) - 3);
+			if (nsgl > chan->vq_sg->nsgl) {
+				pr_info("limiting 'msize' to %d as only %d "
+					"of %zu SG lists could be allocated",
+					client->trans_maxsize,
+					chan->vq_sg->nsgl, nsgl);
 			}
 		}
 #endif /* CONFIG_ARCH_NO_SG_CHAIN */
-- 
2.20.1


      parent reply	other threads:[~2021-09-22 17:30 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-22 16:00 [PATCH v3 0/7] net/9p: remove msize limit in virtio transport Christian Schoenebeck
2021-09-22 16:00 ` [PATCH v3 1/7] net/9p: show error message if user 'msize' cannot be satisfied Christian Schoenebeck
2021-09-22 16:00 ` [PATCH v3 2/7] 9p/trans_virtio: separate allocation of scatter gather list Christian Schoenebeck
2021-09-22 16:00 ` [PATCH v3 3/7] 9p/trans_virtio: turn amount of sg lists into runtime info Christian Schoenebeck
2021-09-22 16:00 ` [PATCH v3 4/7] 9p/trans_virtio: introduce struct virtqueue_sg Christian Schoenebeck
2021-09-22 16:00 ` [PATCH v3 5/7] net/9p: add trans_maxsize to struct p9_client Christian Schoenebeck
2021-09-22 16:00 ` [PATCH v3 6/7] 9p/trans_virtio: support larger msize values Christian Schoenebeck
2021-11-20 11:20   ` Nikolay Kichukov
2021-11-20 11:45     ` Dominique Martinet
2021-11-20 14:46       ` Christian Schoenebeck
2021-11-20 21:28         ` Nikolay Kichukov
2021-11-20 23:02         ` Dominique Martinet
2021-11-21 16:57           ` Christian Schoenebeck
2021-11-21 22:12             ` Dominique Martinet
2021-11-22 13:32               ` Christian Schoenebeck
2021-11-22 22:35                 ` Dominique Martinet
2021-11-24 12:22                   ` Christian Schoenebeck
2021-09-22 16:00 ` Christian Schoenebeck [this message]

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