linux-kernel - RE: [PATCH v2 1/3] iommufd: Add devices_users to track the hw

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Message-ID: <DS0PR11MB7529E920AE8F2CF39135CFE9C3D39@DS0PR11MB7529.namprd11.prod.outlook.com>
Date:   Mon, 30 Jan 2023 02:22:20 +0000
From:   "Liu, Yi L" <yi.l.liu@...el.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        Nicolin Chen <nicolinc@...dia.com>,
        "jgg@...dia.com" <jgg@...dia.com>
CC:     "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2 1/3] iommufd: Add devices_users to track the
 hw_pagetable usage by device

> From: Tian, Kevin <kevin.tian@...el.com>
> Sent: Sunday, January 29, 2023 5:23 PM
>
> > hw_pagetable by the attached devices. Make this field as a pointer, only
> > allocate for a stage-2 hw_pagetable. A stage-1 hw_pagetable should
> reuse
> > the stage-2 hw_pagetable's devices_users, because when a device
> attaches
> > to a stage-1 hw_pagetable, linking the stage-2 hwpt to the IOAS is still
> > required. So, with a nested configuration, increase the devices_users on
> > the stage-2 (parent) hwpt, no matter a device is attached to the stage-1
> > or the stage-2 hwpt.
> 
> Above is very confusing w/o seeing the full series of nesting support.
> 
> As a preparatory step this should focus on existing code and what this
> series tries to achieve. e.g. I'd not make device_users a pointer here.
> Do that incrementally when the nesting support comes.

Yes, in the below branch, I've moved this patch to be together with the nesting
commits. Maybe I can send out the nesting RFC.

https://github.com/yiliu1765/iommufd/commits/wip/iommufd-v6.2-rc4-nesting

Regards,
Yi Liu