On 1.10.2025 4.45, John Hubbard wrote: > On 9/30/25 6:39 PM, Alexandre Courbot wrote: >> On Wed Oct 1, 2025 at 10:26 AM JST, John Hubbard wrote: >>> On 9/30/25 5:26 PM, Alexandre Courbot wrote: >>>> On Wed Oct 1, 2025 at 7:07 AM JST, John Hubbard wrote: >>>>> Post-Kangrejos, the approach for NovaCore + VFIO has changed a bit: the >>>>> idea now is that VFIO drivers, for NVIDIA GPUs that are supported by >>>>> NovaCore, should bind directly to the GPU's VFs. (An earlier idea was to >>>>> let NovaCore bind to the VFs, and then have NovaCore call into the upper >>>>> (VFIO) module via Aux Bus, but this turns out to be awkward and is no >>>>> longer in favor.) So, in order to support that: >>>>> >>>>> Nova-core must only bind to Physical Functions (PFs) and regular PCI >>>>> devices, not to Virtual Functions (VFs) created through SR-IOV. >>>> >>>> Naive question: will guests also see the passed-through VF as a VF? If >>>> so, wouldn't this change also prevents guests from using Nova? >>>
pdev->virtfn (VF) is set to "true" when admin enabling VFs via the sysfs and PF driver. Presumably, pdev->virtfn will be "false" all the time in the guest. >>> I'm also new to this area. I would expect that guests *must* see >>> these as PFs, otherwise...nothing makes any sense. >> >> But if the guest sees the passed-through VF as a PF, won't it try to >> do things it is not supposed to do like loading the GSP firmware (which >> is managed by the host)? > The guest driver will read PMC_BOOT_1 and check PMC_BOOT_1_VGPU_VF flag to tell if it is running on a VF or a PF. https://github.com/NVIDIA/open-gpu-kernel-modules/blob/main/src/nvidia/arch/nvalloc/unix/src/os-hypervisor.c#L945 > Yes. A non-paravirtualized guest will attempt to behave just like a > bare metal driver would behave. It's the job of the various layers > of virtualization to intercept and modify such things appropriately. > > Looking ahead: if the VFIO experts come back and tell us that guests > see these as VFs, then there is still a way forward, because we > talked about loading nova-core with a "vfio_mode" kernel module > parameter. So then it becomes "if vfio_mode, then skip VFs". > > > thanks,
