Re: [PATCH 1/1] iommu/vt-d: Enable PASID during iommu device probe

[Baolu Lu]

Hi Ethan,

On 2022/9/13 15:46, Ethan Zhao wrote:
> Baolu,
>
> 在 2022/9/12 10:48, Lu Baolu 写道:
> > Previously PASID supports on both IOMMU and PCI devices are enabled in 
> > the
> > iommu_dev_enable_feature(dev, IOMMU_DEV_FEAT_SVA) path. It's functionally
> > correct as the SVA is the only feature that requires PASID setup. 
> > However,
> > looking ahead, we will add more features that need to enable pasid (for
> > example, kernel DMA with PASID, SIOV, VM guest SVA, etc.). It makes more
> > sense to enable PASID during iommu probing device.
> >
> > This enables PASID during iommu probing device and deprecates the
> > intel_iommu_enable_pasid() helper. This is safe because the IOMMU 
> > hardware
> > will block any PCI TLP with a PASID prefix if there is no IOMMU domain
> > attached to the PASID of the device.
>
> What the error path would be if this code runs on some old platforms don't
>
> support PASID, would you print out "this platform doesn't suppor PASID" and
>
> give users an interface function to query if the PASID cap of iommu is 
> enabled
>
> and if not why ?

It's not an error case if the IOMMU doesn't support PASID. But it's an
error case if any device drivers call PASID related IOMMU interfaces
(for example, iommu_domain_attach/detach_dev_pasid()). The corresponding
error code will be returned to the drivers.

Best regards,
baolu