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

[Dr. David Alan Gilbert]

* Eric Auger (eric.auger@redhat.com) wrote:
> 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.

I'm not sure about users of this; if no one has used it then yeh; you
could bump up the version_id to make it a bit clearer.

Dave

> 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),
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK