>-----Original Message-----
>From: Jason Gunthorpe <j...@nvidia.com>
>Subject: Re: [PATCH rfcv3 15/21] intel_iommu: Bind/unbind guest page table to
>host
>
>On Tue, Jun 17, 2025 at 09:03:32PM +0800, Yi Liu wrote:
>> > I suggest fixing the Linux driver to refuse to run in sm_on mode if
>> > the HW supports scalable mode and ecap_slts = false. That may not be
>> > 100% spec compliant but it seems like a reasonable approach.
>>
>> running sm_on with only ecap_flts==true is what we want here. We want
>> the guest use stage-1 page table hence it can be used by hw under the
>> nested translation mode. While this page table is only available in sm_on
>> mode.
>>
>> If we want to drop the legacy mode usage in virtualization environment, we
>> might let linux iommu driver refuse running legacy mode while ecap_slts is
>> false. I suppose HW is going to advertise both ecap_slts and ecap_flts. So
>> this will just let guest get rid of using legacy mode.
>>
>> But this is not necessary so far. As the discussion going here, we intend
>> to reuse the GPA HWPT allocated by VFIO container as well.[1] This is now
>> aligned with Nic and Shameer.
>
>I think it is an issue, nobody really wants to accidently start
>supporting and using shadow mode just because the VM is misconfigured.
>
>What is desirable is to make this automatic and ensure we stay in the
>nesting configuration only.
This will break QEMU's back compatibility. Current QEMU supports legacy
mode when ecap_flts==true, but a newer QEMU not?
Thanks
Zhenzhong
