linux-kernel - RE: [PATCH v2 07/10] iommufd/device: Make hwpt_list list

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Date:   Mon, 13 Feb 2023 02:12:49 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Jason Gunthorpe <jgg@...dia.com>
CC:     Nicolin Chen <nicolinc@...dia.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "will@...nel.org" <will@...nel.org>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "shuah@...nel.org" <shuah@...nel.org>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>
Subject: RE: [PATCH v2 07/10] iommufd/device: Make hwpt_list list_add/del
 symmetric

> From: Jason Gunthorpe <jgg@...dia.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