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

[Eric Auger <eric.auger@redhat.com>]

Hi Dave,

On 1/31/22 2:07 PM, Dr. David Alan Gilbert wrote:
> * 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.

Thank you for your input. Yes to me it sounds OK to only bump the
version_id while adding the new field.

Eric
>
> 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),