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

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Date:   Wed, 5 May 2021 14:28:53 +1000
From:   Alexey Kardashevskiy <aik@...abs.ru>
To:     Jason Gunthorpe <jgg@...dia.com>,
        David Gibson <david@...son.dropbear.id.au>
Cc:     Alex Williamson <alex.williamson@...hat.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Auger Eric <eric.auger@...hat.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        "Tian, Kevin" <kevin.tian@...el.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>,
        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



On 05/05/2021 04:15, Jason Gunthorpe wrote:
> On Tue, May 04, 2021 at 01:54:55PM +1000, David Gibson wrote:
>> On Mon, May 03, 2021 at 01:05:30PM -0300, Jason Gunthorpe wrote:
>>> On Thu, Apr 29, 2021 at 01:20:22PM +1000, David Gibson wrote:
>>>>> There is a certain appeal to having some
>>>>> 'PPC_TCE_CREATE_SPECIAL_IOASID' entry point that has a wack of extra
>>>>> information like windows that can be optionally called by the viommu
>>>>> driver and it remains well defined and described.
>>>>
>>>> Windows really aren't ppc specific.  They're absolutely there on x86
>>>> and everything else as well - it's just that people are used to having
>>>> a window at 0..<something largish> that you can often get away with
>>>> treating it sloppily.
>>>
>>> My point is this detailed control seems to go on to more than just
>>> windows. As you say the vIOMMU is emulating specific HW that needs to
>>> have kernel interfaces to match it exactly.
>>
>> It's really not that bad.  The case of emulating the PAPR vIOMMU on
>> something else is relatively easy, because all updates to the IO page
>> tables go through hypercalls.  So, as long as the backend IOMMU can
>> map all the IOVAs that the guest IOMMU can, then qemu's implementation
>> of those hypercalls just needs to put an equivalent mapping in the
>> backend, which it can do with a generic VFIO_DMA_MAP.
> 
> So you also want the PAPR vIOMMU driver to run on, say, an ARM IOMMU?


This is a good feature in general when let's say there is a linux 
supported device which has a proprietary device firmware update tool 
which only exists as an x86 binary and your hardware is not x86 - 
running qemu + vfio in full emulation would provide a way to run the 
tool to update a physical device.


-- 
Alexey