netdev - Re: [PATCH v2] vhost/vdpa: Add MSI translation tables to iommu for software-managed MSI

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Date:   Thu, 23 Mar 2023 17:22:36 +0800
From:   Nanyong Sun <sunnanyong@...wei.com>
To:     Jason Gunthorpe <jgg@...dia.com>,
        "Michael S. Tsirkin" <mst@...hat.com>
CC:     Jason Wang <jasowang@...hat.com>, <joro@...tes.org>,
        <will@...nel.org>, <robin.murphy@....com>, <iommu@...ts.linux.dev>,
        <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>,
        <virtualization@...ts.linux-foundation.org>,
        <netdev@...r.kernel.org>, <wangrong68@...wei.com>,
        Cindy Lu <lulu@...hat.com>
Subject: Re: [PATCH v2] vhost/vdpa: Add MSI translation tables to iommu for
 software-managed MSI


On 2023/3/10 20:36, Jason Gunthorpe wrote:
> On Fri, Mar 10, 2023 at 04:53:42AM -0500, Michael S. Tsirkin wrote:
>> On Fri, Mar 10, 2023 at 05:45:46PM +0800, Jason Wang wrote:
>>> On Fri, Mar 10, 2023 at 4:41 PM Michael S. Tsirkin <mst@...hat.com> wrote:
>>>> On Mon, Feb 20, 2023 at 10:37:18AM +0800, Jason Wang wrote:
>>>>> On Fri, Feb 17, 2023 at 8:43 PM Jason Gunthorpe <jgg@...dia.com> wrote:
>>>>>> On Fri, Feb 17, 2023 at 05:12:29AM -0500, Michael S. Tsirkin wrote:
>>>>>>> On Thu, Feb 16, 2023 at 08:14:50PM -0400, Jason Gunthorpe wrote:
>>>>>>>> On Tue, Feb 07, 2023 at 08:08:43PM +0800, Nanyong Sun wrote:
>>>>>>>>> From: Rong Wang <wangrong68@...wei.com>
>>>>>>>>>
>>>>>>>>> Once enable iommu domain for one device, the MSI
>>>>>>>>> translation tables have to be there for software-managed MSI.
>>>>>>>>> Otherwise, platform with software-managed MSI without an
>>>>>>>>> irq bypass function, can not get a correct memory write event
>>>>>>>>> from pcie, will not get irqs.
>>>>>>>>> The solution is to obtain the MSI phy base address from
>>>>>>>>> iommu reserved region, and set it to iommu MSI cookie,
>>>>>>>>> then translation tables will be created while request irq.
>>>>>>>> Probably not what anyone wants to hear, but I would prefer we not add
>>>>>>>> more uses of this stuff. It looks like we have to get rid of
>>>>>>>> iommu_get_msi_cookie() :\
>>>>>>>>
>>>>>>>> I'd like it if vdpa could move to iommufd not keep copying stuff from
>>>>>>>> it..
>>>>>>> Absolutely but when is that happening?
>>>>>> Don't know, I think it has to come from the VDPA maintainers, Nicolin
>>>>>> made some drafts but wasn't able to get it beyond that.
>>>>> Cindy (cced) will carry on the work.
>>>>>
>>>>> Thanks
>>>> Hmm didn't see anything yet. Nanyong Sun maybe you can take a look?
>>> Just to clarify, Cindy will work on the iommufd conversion for
>>> vhost-vDPA, the changes are non-trivial and may take time. Before we
>>> are able to achieve that,  I think we still need something like this
>>> patch to make vDPA work on software managed MSI platforms.
>>>
>>> Maybe Nanyong can post a new version that addresses the comment so far?
>>>
>>> Thanks
>> Maybe but an ack from iommu maintainers will be needed anyway. Let's see
>> that version, maybe split the export to a patch by itself to make the
>> need for that ack clear.
> A patch to export that function is alread posted:
>
> https://lore.kernel.org/linux-iommu/BN9PR11MB52760E9705F2985EACCD5C4A8CBA9@BN9PR11MB5276.namprd11.prod.outlook.com/T/#u
>
> But I do not want VDPA to mis-use it unless it also implements all the
> ownership stuff properly.
>
> Jason
> .
I want to confirm if we need to introduce iommu group logic to vdpa, as 
"all the ownership stuff" ?