On Fri, Dec 06, 2024 at 03:57:39PM +0800, Yi Liu wrote: > Hi Jason, Vasant, > > When cooking new version, I got three opens on enforcing using > pasid-compatible domains to pasid-capable device in iommufd as suggested > in [1]. > > - Concept problem when considering nested domain > IIUC. pasid-compatible domain means the domain can be attached to PASID. > e.g. AMD requires using V2 page table hence it can be configed to GCR3. > However, the nested domain uses both V1 and V2 page table, I don't think > it can be attached to PASID on AMD. So nested domain can not be > considered as pasid-compatible. Yes. > Based on this, this enforcement only > applies to paging-domains. If so, do we still need to enforce it in > iommufd? Will it simpler to let the AMD iommu driver to deal it? I think driver should deal with it, Intel doesn't have that limitation. I sent patches to fix that detection for AMD and ARM already. > - PASID-capable device v.s. PASID-enabled device > We keep saying PASID-capable, but system may not enable it. Would it > better enforce the pasid-compatible domain for PASID-enabled device? > Seems all iommu vendor will enable PASID if it's supported. But > conceptly, it is be more accurate if only do it when PASID is > enabled. If we want to do more here we should put the core code in charge of deciding of a device will be PASID enabled and the IOMMU driver only indicates if it can be PASID supported. > For PCI devices, we can check if the pasid cap is enabled from device > config space. But for non-PCI PASID support (e.g. some ARM platform), I > don't know if there is any way to check the PASID enabled or not. Or, to > cover both, we need an iommu API to check PASID enabled or not? Yes, some iommu API, I suggest a flag in the common iommu_device. We already have max_pasids there, it may already be nearly enough. > - Nest parent domain should never be pasid-compatible? Up to the driver. > I think the AMD iommu uses the V1 page table format for the parent > domain. Hence parent domain should not be allocated with the > IOMMU_HWPT_ALLOC_PASID flag. Otherwise, it does not work. Should this > be enforced in iommufd? Enforced in the driver. iommufd should enforce that the domain was created with IOMMU_HWPT_ALLOC_PASID before passing the HWPT to any pasid attach/replace function. Jason
