@@ -36,6 +36,16 @@
#include <linux/virtio_9p.h>
#include "trans_common.h"
+/*
+ * Maximum amount of virtio descriptors allowed per virtio round-trip
+ * message.
+ *
+ * This effectively limits msize to (slightly below) 4M, virtio transport
+ * actually supports much more, but client still uses linear buffers, which
+ * in turn are limited to KMALLOC_MAX_SIZE (4M).
+ */
+#define VIRTIO_MAX_DESCRIPTORS 1024
+
/**
* struct virtqueue_sg - (chained) scatter gather lists for virtqueue data
* transmission
@@ -203,6 +213,31 @@ static struct virtqueue_sg *vq_sg_alloc(unsigned int nsgl)
return vq_sg;
}
+/**
+ * vq_sg_resize - resize passed virtqueue scatter/gather lists to the passed
+ * amount of lists
+ * @_vq_sg: scatter/gather lists to be resized
+ * @nsgl: new amount of scatter/gather lists
+ */
+static int vq_sg_resize(struct virtqueue_sg **_vq_sg, unsigned int nsgl)
+{
+ struct virtqueue_sg *vq_sg;
+
+ BUG_ON(!_vq_sg || !nsgl);
+ vq_sg = *_vq_sg;
+ if (vq_sg->nsgl == nsgl)
+ return 0;
+
+ /* lazy resize implementation for now */
+ vq_sg = vq_sg_alloc(nsgl);
+ if (!vq_sg)
+ return -ENOMEM;
+
+ kfree(*_vq_sg);
+ *_vq_sg = vq_sg;
+ return 0;
+}
+
/**
* p9_virtio_close - reclaim resources of a channel
* @client: client instance
@@ -774,6 +809,10 @@ p9_virtio_create(struct p9_client *client, const char *devname, char *args)
struct virtio_chan *chan;
int ret = -ENOENT;
int found = 0;
+#if !defined(CONFIG_ARCH_NO_SG_CHAIN)
+ size_t npages;
+ size_t nsgl;
+#endif
if (devname == NULL)
return -EINVAL;
@@ -796,6 +835,46 @@ p9_virtio_create(struct p9_client *client, const char *devname, char *args)
return ret;
}
+ /*
+ * if user supplied an 'msize' option that's larger than what this
+ * transport supports by default, then try to allocate more sg lists
+ */
+ if (client->msize > client->trans_maxsize) {
+#ifdef CONFIG_ARCH_NO_SG_CHAIN
+ pr_info("limiting 'msize' to %d because architecture does not "
+ "support chained scatter gather lists\n",
+ client->trans_maxsize);
+#else
+ npages = DIV_ROUND_UP(client->msize, PAGE_SIZE);
+ if (npages > VIRTIO_MAX_DESCRIPTORS)
+ npages = VIRTIO_MAX_DESCRIPTORS;
+ if (npages > chan->p9_max_pages) {
+ npages = chan->p9_max_pages;
+ pr_info("limiting 'msize' as it would exceed the max. "
+ "of %lu pages allowed on this system\n",
+ chan->p9_max_pages);
+ }
+ nsgl = DIV_ROUND_UP(npages, SG_USER_PAGES_PER_LIST);
+ if (nsgl > chan->vq_sg->nsgl) {
+ /*
+ * if resize fails, no big deal, then just continue with
+ * whatever we got
+ */
+ if (!vq_sg_resize(&chan->vq_sg, nsgl)) {
+ /*
+ * decrement 2 pages as both 9p request and 9p reply have
+ * to fit into the virtio round-trip message
+ */
+ client->trans_maxsize =
+ PAGE_SIZE *
+ clamp_t(int,
+ (nsgl * SG_USER_PAGES_PER_LIST) - 2,
+ 0, VIRTIO_MAX_DESCRIPTORS - 2);
+ }
+ }
+#endif /* CONFIG_ARCH_NO_SG_CHAIN */
+ }
+
client->trans = (void *)chan;
client->status = Connected;
chan->client = client;
The virtio transport supports by default a 9p 'msize' of up to approximately 500 kB. This patch adds support for larger 'msize' values by resizing the amount of scatter/gather lists if required. To be more precise, for the moment this patch increases the 'msize' limit for the virtio transport to slightly below 4 MB, virtio transport actually supports much more (tested successfully with an experimental QEMU version and some dirty 9p Linux client hacks up to msize=128MB), but client still uses linear buffers, which in turn are limited to KMALLOC_MAX_SIZE (4M). Signed-off-by: Christian Schoenebeck <linux_oss@crudebyte.com> --- I am not sure if it is safe the way SG lists are resized here. I "think" Dominique said before there should be no concurrency here, but probably deserves a revisit. net/9p/trans_virtio.c | 79 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 79 insertions(+)