linux-kernel - RE: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and allocation APIs

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Date:   Wed, 31 Mar 2021 07:41:40 +0000
From:   "Liu, Yi L" <yi.l.liu@...el.com>
To:     Jason Gunthorpe <jgg@...dia.com>,
        "Tian, Kevin" <kevin.tian@...el.com>
CC:     Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        David Woodhouse <dwmw2@...radead.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        Tejun Heo <tj@...nel.org>, Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>,
        "Jean-Philippe Brucker" <jean-philippe@...aro.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Eric Auger <eric.auger@...hat.com>,
        "Jonathan Corbet" <corbet@....net>,
        "Raj, Ashok" <ashok.raj@...el.com>, "Wu, Hao" <hao.wu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>
Subject: RE: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and allocation
 APIs

> From: Jason Gunthorpe <jgg@...dia.com>
> Sent: Tuesday, March 30, 2021 9:28 PM
> 
> On Tue, Mar 30, 2021 at 04:14:58AM +0000, Tian, Kevin wrote:
> 
> > One correction. The mdev should still construct the list of allowed PASID's
> as
> > you said (by listening to IOASID_BIND/UNBIND event), in addition to the
> ioasid
> > set maintained per VM (updated when a PASID is allocated/freed). The
> per-VM
> > set is required for inter-VM isolation (verified when a pgtable is bound to
> the
> > mdev/PASID), while the mdev's own list is necessary for intra-VM isolation
> when
> > multiple mdevs are assigned to the same VM (verified before loading a
> PASID
> > to the mdev). This series just handles the general part i.e. per-VM ioasid
> set and
> > leaves the mdev's own list to be managed by specific mdev driver which
> listens
> > to various IOASID events).
> 
> This is better, but I don't understand why we need such a convoluted
> design.
> 
> Get rid of the ioasid set.
>
> Each driver has its own list of allowed ioasids.

First, I agree with you it's necessary to have a per-device allowed ioasid
list. But besides it, I think we still need to ensure the ioasid used by a
VM is really allocated to this VM. A VM should not use an ioasid allocated
to another VM. right? Actually, this is the major intention for introducing
ioasid_set.

> Register a ioasid in the driver's list by passing the fd and ioasid #

The fd here is a device fd. Am I right? If yes, your idea is ioasid is
allocated via /dev/ioasid and associated with device fd via either VFIO
or vDPA ioctl. right? sorry I may be asking silly questions but really
need to ensure we are talking in the same page.

> No listening to events. A simple understandable security model.

For this suggestion, I have a little bit concern if we may have A-B/B-A
lock sequence issue since it requires the /dev/ioasid (if it supports)
to call back into VFIO/VDPA to check if the ioasid has been registered to
device FD and record it in the per-device list. right? Let's have more
discussion based on the skeleton sent by Kevin.

Regards,
Yi Liu