linux-kernel - Re: [PATCH v2 06/19] iommufd/viommu: Add IOMMU_VIOMMU_SET/UNSET_VDEV

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Message-ID: <e574e1d0-b003-462d-9a59-ef16e95b7766@amd.com>
Date: Sat, 10 May 2025 22:51:58 +1000
From: Alexey Kardashevskiy <aik@....com>
To: Jason Gunthorpe <jgg@...dia.com>
Cc: Nicolin Chen <nicolinc@...dia.com>, kevin.tian@...el.com,
 will@...nel.org, joro@...tes.org, suravee.suthikulpanit@....com,
 robin.murphy@....com, dwmw2@...radead.org, baolu.lu@...ux.intel.com,
 shuah@...nel.org, linux-kernel@...r.kernel.org, iommu@...ts.linux.dev,
 linux-arm-kernel@...ts.infradead.org, linux-kselftest@...r.kernel.org,
 eric.auger@...hat.com, jean-philippe@...aro.org, mdf@...nel.org,
 mshavit@...gle.com, shameerali.kolothum.thodi@...wei.com,
 smostafa@...gle.com, yi.l.liu@...el.com
Subject: Re: [PATCH v2 06/19] iommufd/viommu: Add
 IOMMU_VIOMMU_SET/UNSET_VDEV_ID ioctl



On 10/5/25 08:07, Jason Gunthorpe wrote:
> On Fri, May 09, 2025 at 12:57:18PM +1000, Alexey Kardashevskiy wrote:
>>
>>
>> On 7/5/25 22:24, Jason Gunthorpe wrote:
>>> On Wed, May 07, 2025 at 09:18:29PM +1000, Alexey Kardashevskiy wrote:
>>>
>>>>> We should not destroy the vdevice for something like that. In a CC
>>>>> case that would unplug it from the VM which is not right.
>>>>
>>>> vdevice is not directly seen by the guest, is not it? The guest will
>>>> see, for example, an "AMD IOMMU" and assume there is device table
>>>> for all 64K devices, and so on, it is QEMU which will be
>>>> reallocating vdevice in the host's IOMMUFD. Did I miss something
>>>> here? Thanks,
>>>
>>> I imagined the vdevice would trigger the CC call to create the vPCI
>>> function in the guest attached to the secure iommu.
>>
>> What is this vPCI going to look like inside the guest? There still
>> be AMD IOMMU PCI function and passed through to-be-trusted PCI
>> function.
> 
> However the VMM tells it to look using the arguments to the create
> vdevice ioctl?
> 
> I don't understand the question?

"We should not destroy the vdevice" confused me. It is not a device which a VM would see (or is it?), it is a QEMU/IOMMUFD object which we can create/destroy at any time (well, may be not, but the VM does not have a say in this). And then this vPCI thing - what is it, synonym to "vdevice" or a different thing?


-- 
Alexey