Re: Qemu and virtio 1.0

Michael S. Tsirkin
2015-03-02T11:43:43Z

On Wed, Feb 25, 2015 at 02:50:22PM +1030, Rusty Russell wrote:
> OK, I am trying to experiment with virtio 1.0 support using the
> latest kernel and MST's qemu tree:
>
> https://git.kernel.org/cgit/virt/kvm/mst/qemu.git/?h=virtio-1.0
>
> The first issue is that the device config endian was wrong (see
> attached patch).
>
> I'm now setting up a BE guest on my x86 laptop, and a BE and LE guest
> on a BE powerpc machine, to check that all combinations work correctly.
> If others test too, that would be appreciated!
>
> Cheers,
> Rusty.

Thanks a lot for finding this!
The issue is certainly there, though I think looking
at guest features is not the right thing to do:
drivers can access config before acking features.

At least for PCI, it's very simple: we have a
separate memory region for modern devices, we
should just use a different accessor, not virtio_config_readw
and friends.

Untested patch sent (sorry about the untested part, a bit busy right now).

> >From 95ac91554ed602f856a2a5fcc25eaffcad1b1c8d Mon Sep 17 00:00:00 2001
> From: Rusty Russell <rusty@rustcorp.com.au>
> Date: Tue, 24 Feb 2015 14:47:44 +1030
> Subject: [PATCH] virtio_config_write*/virtio_config_read*: Don't endian swap
> for virtio 1.0.
>
> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
>
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index 079944c..882a31b 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -662,7 +662,12 @@ uint32_t virtio_config_readw(VirtIODevice *vdev, uint32_t addr)
>
> k->get_config(vdev, vdev->config);
>
> - val = lduw_p(vdev->config + addr);
> + /* Virtio 1.0 is always LE */
> + if (virtio_has_feature(vdev, VIRTIO_F_VERSION_1)) {
> + val = lduw_le_p(vdev->config + addr);
> + } else {
> + val = lduw_p(vdev->config + addr);
> + }
> return val;
> }
>
> @@ -677,7 +682,12 @@ uint32_t virtio_config_readl(VirtIODevice *vdev, uint32_t addr)
>
> k->get_config(vdev, vdev->config);
>
> - val = ldl_p(vdev->config + addr);
> + /* Virtio 1.0 is always LE */
> + if (virtio_has_feature(vdev, VIRTIO_F_VERSION_1)) {
> + val = ldl_le_p(vdev->config + addr);
> + } else {
> + val = ldl_p(vdev->config + addr);
> + }
> return val;
> }
>
> @@ -706,7 +716,12 @@ void virtio_config_writew(VirtIODevice *vdev, uint32_t addr, uint32_t data)
> return;
> }
>
> - stw_p(vdev->config + addr, val);
> + /* Virtio 1.0 is always LE */
> + if (virtio_has_feature(vdev, VIRTIO_F_VERSION_1)) {
> + stw_le_p(vdev->config + addr, val);
> + } else {
> + stw_p(vdev->config + addr, val);
> + }
>
> if (k->set_config) {
> k->set_config(vdev, vdev->config);
> @@ -722,7 +737,12 @@ void virtio_config_writel(VirtIODevice *vdev, uint32_t addr, uint32_t data)
> return;
> }
>
> - stl_p(vdev->config + addr, val);
> + /* Virtio 1.0 is always LE */
> + if (virtio_has_feature(vdev, VIRTIO_F_VERSION_1)) {
> + stl_le_p(vdev->config + addr, val);
> + } else {
> + stl_p(vdev->config + addr, val);
> + }
>
> if (k->set_config) {
> k->set_config(vdev, vdev->config);