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From: Michael S. Tsirkin on 5 Aug 2010 16:20
qemu supports up to UIO_MAXIOV s/g so we have to match that.
Apparently windows guests rely on this (more precisely,
they want to fill all of vq with s/g entries of a single
descriptor).

Allocate indirect and log arrays dynamically to avoid
using too much contigious memory.
hdr array is used to store the virtio header.
Since each iovec entry has >= 1 byte length, we never need
more than header length entries to store the header.

Signed-off-by: Michael S. Tsirkin <mst(a)redhat.com>

---

This fixes Red Hat bugzilla 619002.
Dave, I'll queue this through the vhost tree so there's no
need for you to apply this.
Labeling RFC to make this explicit.


drivers/vhost/vhost.c | 32 ++++++++++++++++++++++++++++++--
drivers/vhost/vhost.h | 17 ++++++++---------
2 files changed, 38 insertions(+), 11 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index e519950..b21a5e5 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -123,10 +123,31 @@ static void vhost_vq_reset(struct vhost_dev *dev,
vq->log_ctx = NULL;
}

+/* Helper to allocate iovec buffers for all vqs. */
+static long vhost_dev_alloc_iovecs(struct vhost_dev *dev)
+{
+ int i;
+ for (i = 0; i < dev->nvqs; ++i) {
+ dev->vqs[i].indirect = kmalloc(GFP_KERNEL, UIO_MAXIOV *
+ sizeof *dev->vqs[i].indirect);
+ dev->vqs[i].log = kmalloc(GFP_KERNEL, UIO_MAXIOV *
+ sizeof *dev->vqs[i].log);
+ if (!dev->vqs[i].indirect || !dev->vqs[i].log)
+ goto err_nomem;
+ }
+ return 0;
+err_nomem:
+ for (; i >= 0; --i) {
+ kfree(dev->vqs[i].indirect);
+ kfree(dev->vqs[i].log);
+ }
+ return -ENOMEM;
+}
+
long vhost_dev_init(struct vhost_dev *dev,
struct vhost_virtqueue *vqs, int nvqs)
{
- int i;
+ int i, ret;
dev->vqs = vqs;
dev->nvqs = nvqs;
mutex_init(&dev->mutex);
@@ -136,6 +157,10 @@ long vhost_dev_init(struct vhost_dev *dev,
dev->mm = NULL;
dev->wq = NULL;

+ ret = vhost_dev_alloc_iovecs(dev);
+ if (ret)
+ return ret;
+
for (i = 0; i < dev->nvqs; ++i) {
dev->vqs[i].dev = dev;
mutex_init(&dev->vqs[i].mutex);
@@ -222,6 +247,9 @@ void vhost_dev_cleanup(struct vhost_dev *dev)
if (dev->vqs[i].call)
fput(dev->vqs[i].call);
vhost_vq_reset(dev, dev->vqs + i);
+
+ kfree(dev->vqs[i].indirect);
+ kfree(dev->vqs[i].log);
}
if (dev->log_ctx)
eventfd_ctx_put(dev->log_ctx);
@@ -824,7 +852,7 @@ static int get_indirect(struct vhost_dev *dev, struct vhost_virtqueue *vq,
}

ret = translate_desc(dev, indirect->addr, indirect->len, vq->indirect,
- ARRAY_SIZE(vq->indirect));
+ UIO_MAXIOV);
if (unlikely(ret < 0)) {
vq_err(vq, "Translation failure %d in indirect.\n", ret);
return ret;
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 19f4334..61b1a6e 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -12,14 +12,10 @@
#include <linux/uio.h>
#include <linux/virtio_config.h>
#include <linux/virtio_ring.h>
+#include <linux/virtio_net.h>

struct vhost_device;

-enum {
- /* Enough place for all fragments, head, and virtio net header. */
- VHOST_NET_MAX_SG = MAX_SKB_FRAGS + 2,
-};
-
/* Poll a file (eventfd or socket) */
/* Note: there's nothing vhost specific about this structure. */
struct vhost_poll {
@@ -83,9 +79,12 @@ struct vhost_virtqueue {
bool log_used;
u64 log_addr;

- struct iovec indirect[VHOST_NET_MAX_SG];
- struct iovec iov[VHOST_NET_MAX_SG];
- struct iovec hdr[VHOST_NET_MAX_SG];
+ struct iovec iov[UIO_MAXIOV];
+ /* hdr is used to store the virtio header.
+ * Since each iovec entry has >= 1 byte length, we never need more than
+ * header length entries to store the header. */
+ struct iovec hdr[sizeof(struct virtio_net_hdr_mrg_rxbuf)];
+ struct iovec *indirect;
size_t hdr_size;
/* We use a kind of RCU to access private pointer.
* All readers access it from workqueue, which makes it possible to
@@ -97,7 +96,7 @@ struct vhost_virtqueue {
void *private_data;
/* Log write descriptors */
void __user *log_base;
- struct vhost_log log[VHOST_NET_MAX_SG];
+ struct vhost_log *log;
};

struct vhost_dev {
--
1.7.2.rc0.14.g41c1c
--
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Prev: [PATCH 5/12] scsi: megaraid_sas - Online Controller Reset (OCR): Add and initialize the OCR relaed variable
Next: [PATCH 6/42] drivers/scsi: Adjust confusing if indentation