Messages in this thread Patch in this message | | | From | Andy Lutomirski <> | Subject | [PATCH] virtio_console: Stop doing DMA on the stack | Date | Tue, 30 Aug 2016 08:04:15 -0700 |
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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> ---
Hi all-
This is currently broken in tip:x86/asm. If you (Amit) like this patch, would it make sense for Ingo to add it to -tip?
Thanks, Andy
drivers/char/virtio_console.c | 23 +++++++++++++++-------- 1 file changed, 15 insertions(+), 8 deletions(-)
diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c index d2406fe25533..5da47e26a012 100644 --- a/drivers/char/virtio_console.c +++ b/drivers/char/virtio_console.c @@ -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; } -- 2.7.4
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