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Re: [Qemu-devel] [PATCH v2 3/8] virtio: Add support for guest setting of
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH v2 3/8] virtio: Add support for guest setting of queue size |
Date: |
Thu, 25 Jul 2013 12:03:17 +0300 |
On Thu, Jul 25, 2013 at 09:50:21AM +0100, Peter Maydell wrote:
> On 25 July 2013 06:38, Michael S. Tsirkin <address@hidden> wrote:
> > On Fri, Jul 12, 2013 at 09:36:57PM +0100, Peter Maydell wrote:
> >> The MMIO virtio transport spec allows the guest to tell the host how
> >> large the queue size is. Add virtio_queue_set_num() function which
> >> implements this in the QEMU common virtio support code.
> >>
> >> Signed-off-by: Peter Maydell <address@hidden>
> >
> > Probably needs to go back to default value on reset?
>
> Tricky, since the default value is "whatever was passed to
> virtio_add_queue()" and we don't save that anywhere.
>
> For virtio-mmio it is a guest bug to fail to write to the
> QueueNum register, so the current behaviour is not out of
> specification (and not harmful either AFAICT).
Best not to leak info across reboots.
Also if guest sets num = 0 it will cause all kind of
harm, no?
> I guess we could add a vring.defaultnum, which would be
> set by virtio_add_queue/virtio_del_queue, and have reset
> copy defaultnum into num. No migration needed for defaultnum
> because it's always the same for a particular qemu config.
Sounds good.
> > Need to migrate?
>
> It's already migrated (though I'm not entirely sure why).
>
> > Is the default value a max legal value? If yes probably a good
> > idea to enforce this.
>
> virtio_add_queue() already enforces this -- it will abort()
> if you try to set up a queue with a default size greater
> than VIRTQUEUE_MAX_SIZE.
No I mean does default value have some meaning?
Does host supply a hint of a max value
besides VIRTQUEUE_MAX_SIZE?
>
> thanks
> -- PMM
- Re: [Qemu-devel] [PATCH v2 8/8] vexpress: Add virtio-mmio transports, (continued)
[Qemu-devel] [PATCH v2 3/8] virtio: Add support for guest setting of queue size, Peter Maydell, 2013/07/12
[Qemu-devel] [PATCH v2 5/8] virtio: Implement MMIO based virtio transport, Peter Maydell, 2013/07/12
[Qemu-devel] [PATCH v2 7/8] vexpress: Make VEDBoardInfo extend arm_boot_info, Peter Maydell, 2013/07/12
[Qemu-devel] [PATCH v2 2/8] arm/boot: Use qemu_devtree_setprop_sized_cells(), Peter Maydell, 2013/07/12