Re: [PATCH v4 06/17] PCI: add SIOV and IMS capability detection

[Thomas Gleixner]

On Mon, Nov 16 2020 at 11:46, Jason Gunthorpe wrote:

> On Mon, Nov 16, 2020 at 07:31:49AM +0000, Tian, Kevin wrote:
>
>> > The subdevices require PASID & IOMMU in native, but inside the guest there
>> > is no
>> > need for IOMMU unless you want to build SVM on top. subdevices work
>> > without
>> > any vIOMMU or hypercall in the guest. Only because they look like normal
>> > PCI devices we could map interrupts to legacy MSIx.
>> 
>> Guest managed subdevices on PF/VF requires vIOMMU. 
>
> Why? I've never heard we need vIOMMU for our existing SRIOV flows in
> VMs??

Handing PF/VF into the guest does not require it.

But if the PF/VF driver in the guest wants to create and manage the
magic mdev subdevices which require PASID support then you surely need
it.

Thanks,

        tglx