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virtio_console: Stop doing DMA on the stack 

virtio_console uses a small DMA buffer for control requests.  Move
that buffer into heap memory.

Doing virtio DMA on the stack is normally okay on non-DMA-API virtio
systems (which is currently most of them), but it breaks completely
if the stack is virtually mapped.

Tested by typing both directions using picocom aimed at /dev/hvc0.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Amit Shah <amit.shah@redhat.com>
This commit is contained in:
Andy Lutomirski 2016-08-30 08:04:15 -07:00 committed by Michael S. Tsirkin
parent af7c1beccf
commit 5e59d9a1ae
1 changed files with 15 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

23
drivers/char/virtio_console.c
View File

@ -165,6 +165,12 @@ struct ports_device {
*/
struct virtqueue *c_ivq, *c_ovq;
/*
* A control packet buffer for guest->host requests, protected
* by c_ovq_lock.
*/
struct virtio_console_control cpkt;
/* Array of per-port IO virtqueues */
struct virtqueue **in_vqs, **out_vqs;
@ -560,28 +566,29 @@ static ssize_t __send_control_msg(struct ports_device *portdev, u32 port_id,
unsigned int event, unsigned int value)
{
struct scatterlist sg[1];
struct virtio_console_control cpkt;
struct virtqueue *vq;
unsigned int len;
if (!use_multiport(portdev))
return 0;
cpkt.id = cpu_to_virtio32(portdev->vdev, port_id);
cpkt.event = cpu_to_virtio16(portdev->vdev, event);
cpkt.value = cpu_to_virtio16(portdev->vdev, value);
vq = portdev->c_ovq;
sg_init_one(sg, &cpkt, sizeof(cpkt));
spin_lock(&portdev->c_ovq_lock);
if (virtqueue_add_outbuf(vq, sg, 1, &cpkt, GFP_ATOMIC) == 0) {
portdev->cpkt.id = cpu_to_virtio32(portdev->vdev, port_id);
portdev->cpkt.event = cpu_to_virtio16(portdev->vdev, event);
portdev->cpkt.value = cpu_to_virtio16(portdev->vdev, value);
sg_init_one(sg, &portdev->cpkt, sizeof(struct virtio_console_control));
if (virtqueue_add_outbuf(vq, sg, 1, &portdev->cpkt, GFP_ATOMIC) == 0) {
virtqueue_kick(vq);
while (!virtqueue_get_buf(vq, &len)
&& !virtqueue_is_broken(vq))
cpu_relax();
}
spin_unlock(&portdev->c_ovq_lock);
return 0;
}