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

Oleksandr
2022-04-17T19:24:08Z

On 16.04.22 01:02, Stefano Stabellini wrote:

Hello Stefano

> On Thu, 14 Apr 2022, Oleksandr Tyshchenko wrote:
>> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>>
>> 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@epam.com>
>> ---
>> 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