>-----Original Message-----
>From: Nicolin Chen <nicol...@nvidia.com>
>Subject: Re: [PATCH rfcv3 15/21] intel_iommu: Bind/unbind guest page table to
>host
>
>On Mon, Jun 16, 2025 at 03:24:06AM +0000, Duan, Zhenzhong wrote:
>> Hi @Liu, Yi L @Nicolin Chen, for emulated/passthru devices
>> behind the same pcie-pci bridge, I think of an idea, adding
>> a new PCI callback:
>>
>> AddressSpace * (*get_address_space_extend)(PCIBus *bus,
>> void *opaque, int devfn, bool accel_dev);
>>
>> which pass in real bus/devfn and a new param accel_dev which
>> is true for vfio device.
>
>Just =y for all vfio (passthrough) devices?
>
>ARM tentatively does this for get_address_space using Shameer's
>trick to detect if the device is a passthrough VFIO one:
>
> PCIDevice *pdev = pci_find_device(bus, pci_bus_num(bus), devfn);
> bool has_iommufd = !!object_property_find(OBJECT(pdev), "iommufd");
>
> if (smmu->nested && ... && has_iommufd) {
> return &sdev->as_sysmem;
> }
>
>So, I guess "accel_dev" could be just:
> !!object_property_find(OBJECT(pdev), "iommufd")
>?
You are right, we don't need param accel_dev. Below should work:
object_dynamic_cast(OBJECT(hiod), TYPE_HOST_IOMMU_DEVICE_IOMMUFD)
>
>> Vtd implements this callback and return separate AS for vfio
>> device if it's under an pcie-pci bridge and flts=on;
>> otherwise it fallback to call .get_address_space(). This way
>> emulated devices and passthru devices behind the same pcie-pci
>> bridge can have different AS.
>
>Again, if "vfio-device" tag with "iommufd" property is enough to
>identify devices to separate their address spaces, perhaps the
>existing get_address_space is enough.
We need get_address_space_extend() to pass real BDF.
get_address_space pass group's BDF which made pci_find_device return wrong
device.
>
>> If above idea is acceptable, then only obstacle is ERRATA_772415,
>> maybe we can let VFIO check this errata and bypass RO mapping from
>> beginning?
>
>Yes. There can be some communication between vIOMMU and the VFIO
>core.
>
>> Or we just block this VFIO device running with flts=on if
>> ERRATA_772415 and suggesting running with flts=off?
>
>That sounds like a simpler solution, so long as nobody complains
>about this limitation :)
I plan to apply this simpler solution except there is objection, because
I don't want to bring complexity to VFIO just for an Errata. I remember
ERRATA_772415 exists only on old SPR, @Liu, Yi L can correct me if I'm wrong.
We can also introduce a new vtd option ignore_errata to force ignore the errata
with a warning message in case user care more on performance over security.
With these two solutions, vtd can reuse VFIO container's IOAS and HWPT just
like ARM, so we are common on this part.
Comments welcome! If no objection, I will apply these solutions in v2.
Thanks
Zhenzhong
