RE: [PATCH v2 1/3] iommu: Make single-device group for PASID explicit

[Tian, Kevin]

> From: Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx>
> Sent: Monday, August 21, 2023 1:45 PM
> 
> On 2023/8/18 11:56, Tian, Kevin wrote:
> >> From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> >> Sent: Monday, August 14, 2023 9:18 AM
> >>
> >> The PASID interfaces have always supported only single-device groups.
> >> This was first introduced in commit 26b25a2b98e45 ("iommu: Bind
> process
> >> address spaces to devices"), and has been kept consistent in subsequent
> >> commits.
> >>
> >> However, the core code doesn't explicitly check for this requirement
> >> after commit 201007ef707a8 ("PCI: Enable PASID only when ACS RR & UF
> >> enabled on upstream path"), which made this requirement implicit.
> >>
> >> Restore the check to make it explicit that the PASID interfaces only
> >> support devices belonging to single-device groups.
> >>
> >> Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> >> ---
> >>   drivers/iommu/iommu.c | 5 +++++
> >>   1 file changed, 5 insertions(+)
> >>
> >> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> >> index 71b9c41f2a9e..f1eba60e573f 100644
> >> --- a/drivers/iommu/iommu.c
> >> +++ b/drivers/iommu/iommu.c
> >> @@ -3408,6 +3408,11 @@ int iommu_attach_device_pasid(struct
> >> iommu_domain *domain,
> >>   		return -ENODEV;
> >>
> >>   	mutex_lock(&group->mutex);
> >> +	if (list_count_nodes(&group->devices) != 1) {
> >> +		ret = -EINVAL;
> >> +		goto out_unlock;
> >> +	}
> >> +
> >
> > I wonder whether we should also block adding new device to this
> > group once the single-device has pasid enabled. Otherwise the
> 
> This has been guaranteed by pci_enable_pasid():
> 
>          if (!pci_acs_path_enabled(pdev, NULL, PCI_ACS_RR | PCI_ACS_UF))
>                  return -EINVAL;
> 

well since you are adding generic core check then it's not good to
rely on the fact of a specific bus...