Re: [PATCH v10 04/12] iommu: Add attach/detach_dev_pasid iommu interface

[Baolu Lu]

On 2022/7/23 22:11, Jason Gunthorpe wrote:
> > +
> > +	/*
> > +	 * Otherwise, the device came from DT/ACPI, assume it is static and
> > +	 * then singleton can know from the device count in the group.
> > +	 */
> > +	return true;
> > +}
> I would be happer if probe was changed to refuse to add a device to a
> group if the group's pasid xarray is not empty, as a protective
> measure.

Agreed. I will add below code.

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 047898666b9f..e43cb6776087 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -895,6 +895,14 @@ int iommu_group_add_device(struct iommu_group 
*group, struct device *dev)
        int ret, i = 0;
        struct group_device *device;

+       /*
+        * The iommu_attach_device_pasid() requires a singleton group.
+        * Refuse to add a device into it if this assumption has been
+        * made.
+        */
+       if (!xa_empty(group->pasid_array))
+               return -EBUSY;
+
        device = kzalloc(sizeof(*device), GFP_KERNEL);
        if (!device)
                return -ENOMEM;

> > +int iommu_attach_device_pasid(struct iommu_domain *domain, struct device *dev,
> > +			      ioasid_t pasid)
> > +{
> > +	struct iommu_group *group;
> > +	void *curr;
> > +	int ret;
> > +
> > +	if (!domain->ops->set_dev_pasid)
> > +		return -EOPNOTSUPP;
> > +
> > +	group = iommu_group_get(dev);
> > +	if (!group || !iommu_group_immutable_singleton(group, dev)) {
> > +		iommu_group_put(group);
> > +		return -EINVAL;
> goto error below
>
> > +	}
> > +
> > +	mutex_lock(&group->mutex);
> Just hold the group->mutex a few lines above and don't put locking in
> iommu_group_immutable_singleton(), it is clearer

Above two comments agreed. iommu_attach_device_pasid() looks like below
after update.

int iommu_attach_device_pasid(struct iommu_domain *domain, struct device 
*dev,
                              ioasid_t pasid)
{
        struct iommu_group *group;
        int ret = -EINVAL;
        void *curr;

        if (!domain->ops->set_dev_pasid)
                return -EOPNOTSUPP;

        group = iommu_group_get(dev);
        if (!group)
                return -ENODEV;

        mutex_lock(&group->mutex);
        if (!iommu_group_immutable_singleton(group, dev))
                goto out_unlock;

        curr = xa_cmpxchg(&group->pasid_array, pasid, NULL, domain, 
GFP_KERNEL);
        if (curr) {
                ret = xa_err(curr) ? : -EBUSY;
                goto out_unlock;
        }
        ret = domain->ops->set_dev_pasid(domain, dev, pasid);
        if (ret)
                xa_erase(&group->pasid_array, pasid);
out_unlock:
        mutex_unlock(&group->mutex);
        iommu_group_put(group);

        return ret;
}

Best regards,
baolu