RE: [PATCH v2 07/10] iommufd/device: Make hwpt_list list_add/del symmetric

From: Jason Gunthorpe jgg@nvidia.com Sent: Saturday, February 11, 2023 5:17 AM

...

there is semantics change.

here is the current code:

case IOMMUFD_OBJ_HW_PAGETABLE: { struct iommufd_hw_pagetable *hwpt = container_of(pt_obj, struct iommufd_hw_pagetable,

obj);

...

rc = iommufd_device_do_attach(idev, hwpt);
if (rc)
	goto out_put_pt_obj;

mutex_lock(&hwpt->ioas->mutex);
list_add_tail(&hwpt->hwpt_item, &hwpt->ioas->hwpt_list);
mutex_unlock(&hwpt->ioas->mutex);
break;

}

Above means every attach to hwpt will try to add the hwpt to the list tail. Isn't it a bug?

Yes, that looks like a bug..

But this patch isn't the right way to fix that.

The HWPT should be permanently linked to the IOAS as long as it exists, and the linkage should happen when it is first created.

So attaching a HWPT to another device should never re-link it to the ioas, thus delete these lines here.

yes, this makes more sense