Re: [RFC PATCH] virtio: make sure legacy pci device gain 32bit-pfn vq

[王贇]

在 2021/12/9 下午2:40, Michael S. Tsirkin 写道:
[snip]
> > > > Besides, I've checked that patch but it can't address our issue, we actually
> > > > have this legacy pci device on arm platform, and the memory layout is
> > > > unfriendly since allocation rarely providing page-address below 44bit, we
> > > > understand the virtio-iommu case should not do force dma, while we don't
> > > > have that so it's just working fine.
> > > >
> > > > Regards,
> > > > Michael Wang
> > >
> > > Hmm wait a sec is it a physical device or a hypervisor?
> > > If a physical one then doesn't it need VIRTIO_F_ORDER_PLATFORM
> > > on ARM?
> >
> > The PCI device is virtual, I can't see how VIRTIO_F_ORDER_PLATFORM help
> > address this issue, legacy pci config is 32bit but it's 36, seems like will
> > never be included?
> >
> > Regards,
> > Michael Wang
>
> Oh, if the device is virtual then I think you should just update it please.
> virtio 0.X is architecturally limited to small VMs,
> if your hypervisor supports more it should emulate virtio 1.0.

I see, nice to confirm the proper approach, although we don't have that 
option on the desk :-P

So as long as we don't have any iommu enabled, the force dma approach 
could be safe, is this correct?

Regards,
Michael Wang

> > > > > > > > ---
> > > > > > > >      drivers/virtio/virtio_pci_legacy.c | 10 ++++++++++
> > > > > > > >      drivers/virtio/virtio_ring.c       |  3 +++
> > > > > > > >      include/linux/virtio.h             |  1 +
> > > > > > > >      3 files changed, 14 insertions(+)
> > > > > > > >
> > > > > > > > diff --git a/drivers/virtio/virtio_pci_legacy.c
> > > > > > > > b/drivers/virtio/virtio_pci_legacy.c
> > > > > > > > index d62e983..11f2ebf 100644
> > > > > > > > --- a/drivers/virtio/virtio_pci_legacy.c
> > > > > > > > +++ b/drivers/virtio/virtio_pci_legacy.c
> > > > > > > > @@ -263,6 +263,16 @@ int virtio_pci_legacy_probe(struct virtio_pci_device
> > > > > > > > *vp_dev)
> > > > > > > >      	vp_dev->setup_vq = setup_vq;
> > > > > > > >      	vp_dev->del_vq = del_vq;
> > > > > > > >
> > > > > > > > +	/*
> > > > > > > > +	 * The legacy pci device requre 32bit-pfn vq,
> > > > > > > > +	 * or setup_vq() will failed.
> > > > > > > > +	 *
> > > > > > > > +	 * Thus we make sure vring_use_dma_api() will
> > > > > > > > +	 * return true during the allocation by marking
> > > > > > > > +	 * force_dma here.
> > > > > > > > +	 */
> > > > > > > > +	vp_dev->vdev.force_dma = true;
> > > > > > > > +
> > > > > > > >      	return 0;
> > > > > > > >
> > > > > > > >      err_iomap:
> > > > > > > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > > > > > > > index 3035bb6..6562e01 100644
> > > > > > > > --- a/drivers/virtio/virtio_ring.c
> > > > > > > > +++ b/drivers/virtio/virtio_ring.c
> > > > > > > > @@ -245,6 +245,9 @@ static inline bool virtqueue_use_indirect(struct
> > > > > > > > virtqueue *_vq,
> > > > > > > >
> > > > > > > >      static bool vring_use_dma_api(struct virtio_device *vdev)
> > > > > > > >      {
> > > > > > > > +	if (vdev->force_dma)
> > > > > > > > +		return true;
> > > > > > > > +
> > > > > > > >      	if (!virtio_has_dma_quirk(vdev))
> > > > > > > >      		return true;
> > > > > > > >
> > > > > > > > diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> > > > > > > > index 41edbc0..a4eb29d 100644
> > > > > > > > --- a/include/linux/virtio.h
> > > > > > > > +++ b/include/linux/virtio.h
> > > > > > > > @@ -109,6 +109,7 @@ struct virtio_device {
> > > > > > > >      	bool failed;
> > > > > > > >      	bool config_enabled;
> > > > > > > >      	bool config_change_pending;
> > > > > > > > +	bool force_dma;
> > > > > > > >      	spinlock_t config_lock;
> > > > > > > >      	spinlock_t vqs_list_lock; /* Protects VQs list access */
> > > > > > > >      	struct device dev;
> > > > > > > > --
> > > > > > > > 1.8.3.1