>-----Original Message-----
>From: Nicolin Chen <nicol...@nvidia.com>
>Subject: Re: [PATCH rfcv3 15/21] intel_iommu: Bind/unbind guest page table to
>host
>
>Sorry for a late reply.
>
>On Wed, May 28, 2025 at 07:12:25AM +0000, Duan, Zhenzhong wrote:
>> >Third, the vSMMU model, for invalidation efficiency and HW Queue
>> >support, isolates all emulated devices out of the nesting-enabled
>> >vSMMU instance, suggested by Jason. So, only passthrough devices
>> >would use the nesting-enabled vSMMU instance, meaning there is no
>> >need of IOMMU_NOTIFIER_IOTLB_EVENTS:
>>
>> I see, then you need to check if there is emulated device under
>> nesting-enabled
>vSMMU and fail if there is.
>
>Shameer is working on a multi-vSMMU model in the QEMU. This gives
>each VM different instances to attach devices. And we do not plan
>to support emulated devices on an nesting enabled vSMMU instance,
>which is a bit different than the VT-d model.
I see.
>
>> >On the other hand, the VT-d model is a bit different. It's a giant
>> >vIOMMU for all devices (either passthrough or emualted). For all
>> >emulated devices, it needs IOMMU_NOTIFIER_IOTLB_EVENTS, i.e. the
>> >iommu address space returned via get_address_space().
>> >
>> >That being said, IOMMU_NOTIFIER_IOTLB_EVENTS should not be needed
>> >for passthrough devices, right?
>>
>> No, even if x-flts=on is configured in QEMU cmdline, that only mean virtual
>> vtd
>> supports stage-1 translation, guest still can choose to run in legacy
>mode(stage2),
>> e.g., with kernel cmdline intel_iommu=on,sm_off
>>
>> So before guest run, we don't know which kind of page table either stage1 or
>stage2
>> for this VFIO device by guest. So we have to use iommu AS to catch stage2's
>MAP event
>> if guest choose stage2.
>
>IIUIC, the guest kernel cmdline can switch the mode between the
>stage1 (nesting) and stage2 (legacy/emulated VT-d), right?
Right. E.g., kexec from "intel_iommu=on,sm_on" to "intel_iommu=on,sm_off",
Then first kernel will run in scalable mode and use stage1(nesting) and second
kernel will run in legacy mode and use stage2.
Zhenzhong
