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

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Message-ID: <20210319112221.5123b984@jacob-builder>
Date:   Fri, 19 Mar 2021 11:22:21 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     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, 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>,
        "Tian, Kevin" <kevin.tian@...el.com>, Yi Liu <yi.l.liu@...el.com>,
        Wu Hao <hao.wu@...el.com>, Dave Jiang <dave.jiang@...el.com>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and
 allocation APIs

Hi Jason,

On Fri, 19 Mar 2021 10:54:32 -0300, Jason Gunthorpe <jgg@...dia.com> wrote:

> On Fri, Mar 19, 2021 at 02:41:32PM +0100, Jean-Philippe Brucker wrote:
> > On Fri, Mar 19, 2021 at 09:46:45AM -0300, Jason Gunthorpe wrote:  
> > > On Fri, Mar 19, 2021 at 10:58:41AM +0100, Jean-Philippe Brucker wrote:
> > >   
> > > > Although there is no use for it at the moment (only two upstream
> > > > users and it looks like amdkfd always uses current too), I quite
> > > > like the client-server model where the privileged process does
> > > > bind() and programs the hardware queue on behalf of the client
> > > > process.  
> > > 
> > > This creates a lot complexity, how do does process A get a secure
> > > reference to B? How does it access the memory in B to setup the HW?  
> > 
> > mm_access() for example, and passing addresses via IPC  
> 
> I'd rather the source process establish its own PASID and then pass
> the rights to use it to some other process via FD passing than try to
> go the other way. There are lots of security questions with something
> like mm_access.
> 

Thank you all for the input, it sounds like we are OK to remove mm argument
from iommu_sva_bind_device() and iommu_sva_alloc_pasid() for now?

Let me try to summarize PASID allocation as below:

Interfaces	| Usage	|  Limit	| bind¹ |User visible
--------------------------------------------------------------------
/dev/ioasid²	| G-SVA/IOVA	|  cgroup	| No	|Yes
--------------------------------------------------------------------
char dev³	| SVA		|  cgroup	| Yes	|No
--------------------------------------------------------------------
iommu driver	| default PASID|  no		| No	|No
--------------------------------------------------------------------
kernel		| super SVA	| no		| yes   |No
--------------------------------------------------------------------

¹ Allocated during SVA bind
² PASIDs allocated via /dev/ioasid are not bound to any mm. But its
  ownership is assigned to the process that does the allocation.
³ Include uacce, other private device driver char dev such as idxd

Currently, the proposed /dev/ioasid interface does not map individual PASID
with an FD. The FD is at the ioasid_set granularity and bond to the current
mm. We could extend the IOCTLs to cover individual PASID-FD passing case
when use cases arise. Would this work?

Thanks,

Jacob