Re: [PATCH 3/3] virtio_pci: Use the DMA API

[Joerg Roedel <jroedel@suse.de>]

On Tue, Oct 27, 2015 at 06:17:10PM -0700, Andy Lutomirski wrote:
> From: Andy Lutomirski <luto@amacapital.net>
> 
> This fixes virtio-pci on platforms and busses that have IOMMUs.  This
> will break the experimental QEMU Q35 IOMMU support until QEMU is
> fixed.  In exchange, it fixes physical virtio hardware as well as
> virtio-pci running under Xen.
> 
> We should clean up the virtqueue API to do its own allocation and
> teach virtqueue_get_avail and virtqueue_get_used to return DMA
> addresses directly.
> 
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
> ---
>  drivers/virtio/virtio_pci_common.h |  3 ++-
>  drivers/virtio/virtio_pci_legacy.c | 19 +++++++++++++++----
>  drivers/virtio/virtio_pci_modern.c | 34 ++++++++++++++++++++++++----------
>  3 files changed, 41 insertions(+), 15 deletions(-)

Same here, you need to call the dma_sync* functions when passing data
from/to the virtio-device.

I think a good test for that is to boot a virtio kvm-guest with
swiotlb=force and see if it still works.



	Joerg