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




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




 


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