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

[Baolu Lu]

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;

> check alone at attach time doesn't mean this group won't be
> expanded to have multiple devices later.

Best regards,
baolu