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

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Date:   Fri, 16 Apr 2021 17:00:45 +0200
From:   Auger Eric <eric.auger@...hat.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     "Liu, Yi L" <yi.l.liu@...el.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        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>,
        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

Hi Jason,

On 4/16/21 4:34 PM, Jason Gunthorpe wrote:
> On Fri, Apr 16, 2021 at 04:26:19PM +0200, Auger Eric wrote:
> 
>> This was largely done during several confs including plumber, KVM forum,
>> for several years. Also API docs were shared on the ML. I don't remember
>> any voice was raised at those moments.
> 
> I don't think anyone objects to the high level ideas, but
> implementation does matter. I don't think anyone presented "hey we
> will tunnel an uAPI through VFIO to the IOMMU subsystem" - did they?

At minimum
https://events19.linuxfoundation.cn/wp-content/uploads/2017/11/Shared-Virtual-Memory-in-KVM_Yi-Liu.pdf

But most obviously everything is documented in
Documentation/userspace-api/iommu.rst where the VFIO tunneling is
clearly stated ;-)

But well let's work together to design a better and more elegant
solution then.

Thanks

Eric
> 
> Look at the fairly simple IMS situation, for example. This was
> presented at plumbers too, and the slides were great - but the
> implementation was too hacky. It required a major rework of the x86
> interrupt handling before it was OK.
> 
> Jason
>