[PATCH v2 01/22] iommufd/viommu: Add driver-allocated vDEVICE support

[Tian, Kevin]

> From: Baolu Lu <baolu.lu at linux.intel.com>
> Sent: Sunday, April 27, 2025 2:24 PM
> 
> On 4/26/25 13:57, Nicolin Chen wrote:
> > @@ -120,6 +128,13 @@ struct iommufd_viommu {
> >    *                    array->entry_num to report the number of handled requests.
> >    *                    The data structure of the array entry must be defined in
> >    *                    include/uapi/linux/iommufd.h
> > + * @vdevice_alloc: Allocate a vDEVICE object and init its driver-level
> structure
> > + *                 or HW procedure. Note that the core-level structure is filled
> > + *                 by the iommufd core after calling this op. @virt_id carries a
> > + *                 per-vIOMMU virtual ID for the driver to initialize its HW.
> 
> I'm wondering whether the 'per-vIOMMU virtual ID' is intended to be
> generic for other features that might require a vdevice. I'm also not
> sure where this virtual ID originates when I read it here. Could it

for PCI it's the virtual BDF in the guest PCI topology, hence provided
by the VMM when calling @vdevice_alloc:

> potentially come from the KVM instance? If so, how about retrieving it
> directly from a struct kvm pointer? My understanding is that vIOMMU in
> IOMMUFD acts as a handle to KVM, so perhaps we should maintain a
> reference to the kvm pointer within the iommufd_viommu structure?
> 

It's OK to maintain a KVM pointer in viommu (for which I recall
such discussion for confidential io), but obviously it's not the
requirement in this series.