Re: [PATCH] vfio/iommufd: no hw_info for mediated devices

[Steven Sistare <steven.sistare@oracle.com>]

On 9/10/2024 3:29 PM, Joao Martins wrote:
> On 10/09/2024 18:40, Steve Sistare wrote:
>> IOMMU_GET_HW_INFO fails for a vfio mediated device (aka mdev), because
>> the devid is associated with kernel type IOMMUFD_OBJ_ACCESS, not
>> IOMMUFD_OBJ_DEVICE.  Assume IOMMU_HW_INFO_TYPE_NONE and proceed.
>>
>> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
> 
>> ---
>>   hw/vfio/iommufd.c | 6 ++++--
>>   1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/hw/vfio/iommufd.c b/hw/vfio/iommufd.c
>> index cb7257b..d8928d4 100644
>> --- a/hw/vfio/iommufd.c
>> +++ b/hw/vfio/iommufd.c
>> @@ -635,6 +635,7 @@ static void vfio_iommu_iommufd_class_init(ObjectClass *klass, void *data)
>>   static bool hiod_iommufd_vfio_realize(HostIOMMUDevice *hiod, void *opaque,
>>                                         Error **errp)
>>   {
>> +    Error *err = NULL;
>>       VFIODevice *vdev = opaque;
>>       HostIOMMUDeviceCaps *caps = &hiod->caps;
>>       enum iommu_hw_info_type type;
>> @@ -645,8 +646,9 @@ static bool hiod_iommufd_vfio_realize(HostIOMMUDevice *hiod, void *opaque,
>>       hiod->agent = opaque;
>>   
>>       if (!iommufd_backend_get_device_info(vdev->iommufd, vdev->devid,
>> -                                         &type, &data, sizeof(data), errp)) {
>> -        return false;
>> +                                         &type, &data, sizeof(data), &err)) {
>> +        warn_report_err(err);
>> +        type = IOMMU_HW_INFO_TYPE_NONE;
>>       }
>>   
>>       hiod->name = g_strdup(vdev->name);
> 
> At least we aren't supposed to call realize() on an mdev.
> 
> See commit 9f17604195c ("vfio/iommufd: Don't initialize nor set a
> HOST_IOMMU_DEVICE with mdev"). There's another refactor later on in commit
> 83a4d596a93 ("vfio/{iommufd, container}: Invoke HostIOMMUDevice::realize()
> during attach_device()") where we also don't realize() when vbasedev->hiod is NULL.
> 
> Unless the stty mdevs aren't matching examples, then this shouldn't be possible
> (I didn't have one with real hw behind to test).
> 
> So if you are hitting this codepath then vbasedev::mdev is false, which I don't
> understand how it's possible?

I exercised this with the mtty sample mdev, and mdev is true:

vfio_mdev  (83b8f4f2-509f-382f-3c1e-e6bfe0fa1001) is_mdev 1
iommufd_cdev_getfd  /dev/vfio/devices/vfio1 (fd=26)
iommufd_backend_connect fd=15 owned=1 users=1
iommufd_cdev_connect_and_bind  [iommufd=15] Successfully bound device 83b8f4f2-509f-382f-3c1e-e6bfe0fa1001 (fd=26): output devid=1
iommufd_backend_alloc_ioas  iommufd=15 ioas=2
iommufd_cdev_alloc_ioas  [iommufd=15] new IOMMUFD container with ioasid=2
iommufd_cdev_attach_ioas_hwpt  [iommufd=15] Successfully attached device 83b8f4f2-509f-382f-3c1e-e6bfe0fa1001 (26) to id=2
iommufd_backend_map_dma  iommufd=15 ioas=2 iova=0x0 size=0xc0000 addr=0x7fb80f600000 readonly=0 (0)
iommufd_backend_map_dma  iommufd=15 ioas=2 iova=0xc0000 size=0x20000 addr=0x7fb80d400000 readonly=1 (0)
iommufd_backend_map_dma  iommufd=15 ioas=2 iova=0x100000 size=0xff00000 addr=0x7fb80f700000 readonly=0 (0)
iommufd_cdev_device_info  83b8f4f2-509f-382f-3c1e-e6bfe0fa1001 (26) num_irqs=5 num_regions=9 flags=2
qemu-kvm: -device vfio-pci,iommufd=iommufd1,sysfsdev=/sys/devices/virtual/mtty/mtty/83b8f4f2-509f-382f-3c1e-e6bfe0fa1001:
   warning: Failed to get hardware info: No such file or directory

My qemu tree is a bit old, I will update and look for the issues you described.

- Steve