Re: [PATCH v5 6/9] iommufd: Fault-capable hwpt attach/detach/replace

[Baolu Lu]

On 5/15/24 4:43 PM, Tian, Kevin wrote:
> > From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > Sent: Tuesday, April 30, 2024 10:57 PM
> > +
> > +int iommufd_fault_domain_replace_dev(struct iommufd_device *idev,
> > +				     struct iommufd_hw_pagetable *hwpt,
> > +				     struct iommufd_hw_pagetable *old)
> > +{
> > +	struct iommu_attach_handle *handle;
> > +	int ret;
> > +
> > +	if (hwpt->fault)
> > +		ret = iommufd_fault_iopf_enable(idev);
> > +	else
> > +		iommufd_fault_iopf_disable(idev);
> > +
> > +	ret = iommu_group_replace_domain(idev->igroup->group, hwpt-
> > > domain);
> > +	if (ret)
> > +		goto out_cleanup;
> > +
> > +	iommufd_auto_response_faults(old, idev);
> > +	handle = iommu_attach_handle_get(idev->igroup->group,
> > IOMMU_NO_PASID, 0);
> > +	handle->idev = idev;
>
> why is auto response required in replace? new requests can come
> after the auto response anyway...
>
> The user should prepare for faults delivered to the old or new hwpt
> in the transition window.

The current design of replace allows switching between one that is not
IOPF-capable and one that is. This implies that if we switch from an
IOPF-capable hwpt to a non-IOPF-capable one, the response queue needs to
be auto responded.

Best regards,
baolu