Re: [PATCH RFC v1 10/11] uapi/virtio-iommu: Add a new request type to send page response

[Vivek Kumar Gautam]

Hi Jean,


On 9/21/21 9:46 PM, Jean-Philippe Brucker wrote:
> On Fri, Apr 23, 2021 at 03:21:46PM +0530, Vivek Gautam wrote:
> > Once the page faults are handled, the response has to be sent to
> > virtio-iommu backend, from where it can be sent to the host to
> > prepare the response to a generated io page fault by the device.
> > Add a new virt-queue request type to handle this.
> >
> > Signed-off-by: Vivek Gautam <vivek.gautam@xxxxxxx>
> > ---
> >   include/uapi/linux/virtio_iommu.h | 18 ++++++++++++++++++
> >   1 file changed, 18 insertions(+)
> >
> > diff --git a/include/uapi/linux/virtio_iommu.h b/include/uapi/linux/virtio_iommu.h
> > index c12d9b6a7243..1b174b98663a 100644
> > --- a/include/uapi/linux/virtio_iommu.h
> > +++ b/include/uapi/linux/virtio_iommu.h
> > @@ -48,6 +48,7 @@ struct virtio_iommu_config {
> >   #define VIRTIO_IOMMU_T_PROBE			0x05
> >   #define VIRTIO_IOMMU_T_ATTACH_TABLE		0x06
> >   #define VIRTIO_IOMMU_T_INVALIDATE		0x07
> > +#define VIRTIO_IOMMU_T_PAGE_RESP		0x08
> >   
> >   /* Status types */
> >   #define VIRTIO_IOMMU_S_OK			0x00
> > @@ -70,6 +71,23 @@ struct virtio_iommu_req_tail {
> >   	__u8					reserved[3];
> >   };
> >   
> > +struct virtio_iommu_req_page_resp {
> > +	struct virtio_iommu_req_head		head;
> > +	__le32					domain;
>
> I don't think we need this field, since the fault report doesn't come with
> a domain.

But here we are sending the response which would be consumed by the vfio 
ultimately. In kvmtool, I am consuming this "virtio_iommu_req_page_resp" 
request in the virtio/iommu driver, extracting the domain from it, and 
using that to call the respective "page_response" ops from 
"vfio_iommu_ops" in the vfio/core driver.

Is this incorrect way of passing on the page-response back to the host 
kernel?

But I think this will have to be worked out with the /dev/iommu framework.

> > +	__le32					endpoint;
> > +#define VIRTIO_IOMMU_PAGE_RESP_PASID_VALID	(1 << 0)
>
> To be consistent with the rest of the document this would be
> VIRTIO_IOMMU_PAGE_RESP_F_PASID_VALID

Sure, will update this.

> > +	__le32					flags;
> > +	__le32					pasid;
> > +	__le32					grpid;
> > +#define VIRTIO_IOMMU_PAGE_RESP_SUCCESS		(0x0)
> > +#define VIRTIO_IOMMU_PAGE_RESP_INVALID		(0x1)
> > +#define VIRTIO_IOMMU_PAGE_RESP_FAILURE		(0x2)
> > +	__le16					resp_code;
> > +	__u8					pasid_valid;
>
> This field isn't needed since there already is
> VIRTIO_IOMMU_PAGE_RESP_PASID_VALID

Yes, sure will remove this field.

> > +	__u8					reserved[9];
> > +	struct virtio_iommu_req_tail		tail;
> > +};
>
> I'd align the size of the struct to 16 bytes, but I don't think that's
> strictly necessary.

Will fix this. Thanks a lot for reviewing.

Best regards
Vivek

> Thanks,
> Jean
>
> > +
> >   struct virtio_iommu_req_attach {
> >   	struct virtio_iommu_req_head		head;
> >   	__le32					domain;
> > --
> > 2.17.1