Hi
>-----Original Message-----
>From: Nicolin Chen <nicol...@nvidia.com>
>Subject: Re: [PATCH v5 07/21] intel_iommu: Introduce a new structure
>VTDHostIOMMUDevice
>
>Hi Zhenzhong/Yi,
>
>On Fri, Aug 22, 2025 at 02:40:45AM -0400, Zhenzhong Duan wrote:
>> @@ -4371,6 +4374,7 @@ static bool vtd_dev_set_iommu_device(PCIBus
>*bus, void *opaque, int devfn,
>> HostIOMMUDevice *hiod,
>Error **errp)
>> {
>> IntelIOMMUState *s = opaque;
>> + VTDHostIOMMUDevice *vtd_hiod;
>> struct vtd_as_key key = {
>> .bus = bus,
>> .devfn = devfn,
>
>I wonder if the bus/devfn here would always reflect the actual BDF
>numbers in this function, on an x86 VM.
devfn is enumerated by QEMU, see do_pci_register_device(), bus number is
enumerated in BIOS or kernel.
So we can't use BDF number as key, we use PCIBus pointer + devfn as the key
instead.
>
>With ARM, when the device is attached to a pxb bus, the bus/devfn
>here are both 0, so PCI_BUILD_BDF() using these two returns 0 too.
>
>QEMU command for the device:
> -device pxb-pcie,id=pcie.1,bus_nr=1,bus=pcie.0 \
> -device arm-smmuv3,primary-bus=pcie.1,id=smmuv3.1,accel=on \
> -device pcie-root-port,id=pcie.port1,bus=pcie.1,chassis=1,io-reserve=0 \
> -device
>vfio-pci-nohotplug,host=0009:01:00.0,bus=pcie.port1,rombar=0,id=dev0,iom
>mufd=iommufd0
>
>QEMU log:
>smmuv3_accel_set_iommu_device: bus=0, devfn=0, sid=0
There is only one device under pcie.port1, devfn is initialized to 0, bus
number isn't enumerated yet during realize() so 0.
>
>The set_iommu_device op is invoked by vfio_pci_realize() where the
>the BDF number won't get ready for this kind of PCI setup until a
>later stage that I can't identify yet..
>
>Given that VTD wants the BDF number too, I start to wonder whether
>the set_iommu_device op is invoked in the right place or not..
>
>Maybe VTD works because it saves the bus pointer v.s. bus_num(=0),
>so its bus_num would be updated when later code calculates the BDF
>number using the saved bus pointer (in the key). Nonetheless, the
>saved devfn (in the key) is 0, which wouldn't be updated later as
>the bus_num. So, if the device is supposed to have a devfn (!=0),
>this wouldn't work?
Both PCIBus pointer and devfn are fixed value for a QEMU instance, never
changed.
Thanks
Zhenzhong
