Re: [PATCH v2 3/4] virtio-iommu: Support bypass domain

[Eric Auger]

Hi Jean,

On 1/27/22 3:29 PM, Jean-Philippe Brucker wrote:
> The driver can create a bypass domain by passing the
> VIRTIO_IOMMU_ATTACH_F_BYPASS flag on the ATTACH request. Bypass domains
> perform slightly better than domains with identity mappings since they
> skip translation.
>
> Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
> ---
>  hw/virtio/virtio-iommu.c | 32 ++++++++++++++++++++++++++++++--
>  1 file changed, 30 insertions(+), 2 deletions(-)
>
> diff --git a/hw/virtio/virtio-iommu.c b/hw/virtio/virtio-iommu.c
> index ec02029bb6..a112428c65 100644
> --- a/hw/virtio/virtio-iommu.c
> +++ b/hw/virtio/virtio-iommu.c
> @@ -43,6 +43,7 @@
>  
>  typedef struct VirtIOIOMMUDomain {
>      uint32_t id;
> +    bool bypass;
I am afraid this will break the migration if you don't change
vmstate_domain.

See static const VMStateDescription vmstate_domain.
Also you need to migrate the new bypass field.

Logically we should handle this with a vmstate subsection I think to
handle migration of older devices. However I doubt the device has been
used in production environment supporting migration so my guess is we
may skip that burden and just add the missing field. Adding Juan, Dave &
Peter for advices.

Thanks

Eric

>      GTree *mappings;
>      QLIST_HEAD(, VirtIOIOMMUEndpoint) endpoint_list;
>  } VirtIOIOMMUDomain;
> @@ -258,12 +259,16 @@ static void virtio_iommu_put_endpoint(gpointer data)
>  }
>  
>  static VirtIOIOMMUDomain *virtio_iommu_get_domain(VirtIOIOMMU *s,
> -                                                  uint32_t domain_id)
> +                                                  uint32_t domain_id,
> +                                                  bool bypass)
>  {
>      VirtIOIOMMUDomain *domain;
>  
>      domain = g_tree_lookup(s->domains, GUINT_TO_POINTER(domain_id));
>      if (domain) {
> +        if (domain->bypass != bypass) {
> +            return NULL;
> +        }
>          return domain;
>      }
>      domain = g_malloc0(sizeof(*domain));
> @@ -271,6 +276,7 @@ static VirtIOIOMMUDomain 
> *virtio_iommu_get_domain(VirtIOIOMMU *s,
>      domain->mappings = g_tree_new_full((GCompareDataFunc)interval_cmp,
>                                     NULL, (GDestroyNotify)g_free,
>                                     (GDestroyNotify)g_free);
> +    domain->bypass = bypass;
>      g_tree_insert(s->domains, GUINT_TO_POINTER(domain_id), domain);
>      QLIST_INIT(&domain->endpoint_list);
>      trace_virtio_iommu_get_domain(domain_id);
> @@ -334,11 +340,16 @@ static int virtio_iommu_attach(VirtIOIOMMU *s,
>  {
>      uint32_t domain_id = le32_to_cpu(req->domain);
>      uint32_t ep_id = le32_to_cpu(req->endpoint);
> +    uint32_t flags = le32_to_cpu(req->flags);
>      VirtIOIOMMUDomain *domain;
>      VirtIOIOMMUEndpoint *ep;
>  
>      trace_virtio_iommu_attach(domain_id, ep_id);
>  
> +    if (flags & ~VIRTIO_IOMMU_ATTACH_F_BYPASS) {
> +        return VIRTIO_IOMMU_S_INVAL;
> +    }
> +
>      ep = virtio_iommu_get_endpoint(s, ep_id);
>      if (!ep) {
>          return VIRTIO_IOMMU_S_NOENT;
> @@ -356,7 +367,12 @@ static int virtio_iommu_attach(VirtIOIOMMU *s,
>          }
>      }
>  
> -    domain = virtio_iommu_get_domain(s, domain_id);
> +    domain = virtio_iommu_get_domain(s, domain_id,
> +                                     flags & VIRTIO_IOMMU_ATTACH_F_BYPASS);
> +    if (!domain) {
> +        /* Incompatible bypass flag */
> +        return VIRTIO_IOMMU_S_INVAL;
> +    }
>      QLIST_INSERT_HEAD(&domain->endpoint_list, ep, next);
>  
>      ep->domain = domain;
> @@ -419,6 +435,10 @@ static int virtio_iommu_map(VirtIOIOMMU *s,
>          return VIRTIO_IOMMU_S_NOENT;
>      }
>  
> +    if (domain->bypass) {
> +        return VIRTIO_IOMMU_S_INVAL;
> +    }
> +
>      interval = g_malloc0(sizeof(*interval));
>  
>      interval->low = virt_start;
> @@ -464,6 +484,11 @@ static int virtio_iommu_unmap(VirtIOIOMMU *s,
>      if (!domain) {
>          return VIRTIO_IOMMU_S_NOENT;
>      }
> +
> +    if (domain->bypass) {
> +        return VIRTIO_IOMMU_S_INVAL;
> +    }
> +
>      interval.low = virt_start;
>      interval.high = virt_end;
>  
> @@ -780,6 +805,9 @@ static IOMMUTLBEntry 
> virtio_iommu_translate(IOMMUMemoryRegion *mr, hwaddr addr,
>              entry.perm = flag;
>          }
>          goto unlock;
> +    } else if (ep->domain->bypass) {
> +        entry.perm = flag;
> +        goto unlock;
>      }
>  
>      found = g_tree_lookup_extended(ep->domain->mappings, 
> (gpointer)(&interval),