Hi Alex,
On 2020/11/17 3:56, Alex Williamson wrote:
On Thu, 12 Nov 2020 10:24:07 +0800
Lu Baolu<baolu.lu@xxxxxxxxxxxxxxx> wrote:
Add API for getting the ioasid of a subdevice (vfio/mdev). This calls
into the backend IOMMU module to get the actual value or error number
if ioasid for subdevice is not supported. The physical device driver
implementations which rely on the vfio/mdev framework for mediated
device user level access could typically consume this interface like
below:
struct device *dev = mdev_dev(mdev);
unsigned int pasid;
int ret;
ret = vfio_subdev_ioasid(dev, &pasid);
if (ret < 0)
return ret;
/* Program device context with pasid value. */
....
Seems like an overly specific callback. We already export means for
you to get a vfio_group, test that a device is an mdev, and get the
iommu device from an mdev. So you can already test whether a given
device is an mdev with an iommu backing device that supports aux
domains. The only missing piece seems to be that you can't get the
domain for a group in order to retrieve the pasid. So why aren't we
exporting a callback that given a vfio_group provides the iommu domain?
Make sense! Thanks for your guidance. :-)
So what we want to export in vfio.c is
struct iommu_domain *vfio_group_get_domain(struct vfio_group *group)
What the callers need to do are:
unsigned int pasid;
struct vfio_group *vfio_group;
struct iommu_domain *iommu_domain;
struct device *dev = mdev_dev(mdev);
struct device *iommu_device = mdev_get_iommu_device(dev);
if (!iommu_device ||
!iommu_dev_feature_enabled(iommu_device, IOMMU_DEV_FEAT_AUX))
return -EINVAL;
vfio_group = vfio_group_get_external_user_from_dev(dev);
if (IS_ERR_OR_NULL(vfio_group))
return -EFAULT;
iommu_domain = vfio_group_get_domain(vfio_group);
if (IS_ERR_OR_NULL(iommu_domain)) {
vfio_group_put_external_user(vfio_group);
return -EFAULT;
}
pasid = iommu_aux_get_pasid(iommu_domain, iommu_device);
if (pasid < 0) {
vfio_group_put_external_user(vfio_group);
return -EFAULT;
}
/* Program device context with pasid value. */
...
/* After use of this pasid */
/* Clear the pasid value in device context */
...
vfio_group_put_external_user(vfio_group);
Do I understand your points correctly?
Best regards,
baolu
