Re: [RFC PATCH 6/6] arm/xen: Assign xen-virtio DMA ops for virtio devices in Xen guests

[Oleksandr <olekstysh@xxxxxxxxx>]

On 16.04.22 01:02, Stefano Stabellini wrote:


Hello Stefano

> On Thu, 14 Apr 2022, Oleksandr Tyshchenko wrote:
> > From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
> >
> > Call xen_virtio_setup_dma_ops() only for Xen-aware virtio devices
> > in Xen guests if restricted access to the guest memory is enabled.
> >
> > Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
> > ---
> >   include/xen/arm/xen-ops.h | 7 +++++++
> >   1 file changed, 7 insertions(+)
> >
> > diff --git a/include/xen/arm/xen-ops.h b/include/xen/arm/xen-ops.h
> > index 621da05..28b2ad3 100644
> > --- a/include/xen/arm/xen-ops.h
> > +++ b/include/xen/arm/xen-ops.h
> > @@ -2,12 +2,19 @@
> >   #ifndef _ASM_ARM_XEN_OPS_H
> >   #define _ASM_ARM_XEN_OPS_H
> >   
> > +#include <linux/virtio_config.h>
> >   #include <xen/swiotlb-xen.h>
> > +#include <xen/xen-ops.h>
> >   
> >   static inline void xen_setup_dma_ops(struct device *dev)
> >   {
> >         if (xen_swiotlb_detect())
> >                 dev->dma_ops = &xen_swiotlb_dma_ops;
> > +
> > +#ifdef CONFIG_XEN_VIRTIO
> > +       if (arch_has_restricted_virtio_memory_access() && 
> > xen_is_virtio_device(dev))
> > +               xen_virtio_setup_dma_ops(dev);
> > +#endif
> This makes sense overall.

thank you


> Considering that the swiotlb-xen case and the
> virtio case are mutually exclusive, I would write it like this:
>
>         if (arch_has_restricted_virtio_memory_access() && 
> xen_is_virtio_device(dev))
>                 xen_virtio_setup_dma_ops(dev);
>         else if (xen_swiotlb_detect())
>                 dev->dma_ops = &xen_swiotlb_dma_ops;

Agree, will do


> There is no need for #ifdef (also see other comments).

Agree, if !CONFIG_XEN_VIRTIO then xen_virtio_ are just stubs.


#ifdef CONFIG_XEN_VIRTIO
void xen_virtio_setup_dma_ops(struct device *dev);
bool xen_is_virtio_device(struct device *dev);
#else
static inline void xen_virtio_setup_dma_ops(struct device *dev)
{
}
static inline bool xen_is_virtio_device(struct device *dev)
{
    return false;
}
#endif /* CONFIG_XEN_VIRTIO */



--
Regards,

Oleksandr Tyshchenko