Re: [PATCH v3 00/10] rust: pci: add abstractions for SR-IOV capability

[Leon Romanovsky <leon@kernel.org>]

On Wed, Mar 04, 2026 at 12:45:51PM -0400, Jason Gunthorpe wrote:
> On Wed, Mar 04, 2026 at 06:27:11PM +0200, Leon Romanovsky wrote:
> > On Wed, Mar 04, 2026 at 03:57:57PM +0100, Danilo Krummrich wrote:
> > > On Wed Mar 4, 2026 at 3:26 PM CET, Leon Romanovsky wrote:
> > > > On Wed, Mar 04, 2026 at 10:18:52AM -0400, Jason Gunthorpe wrote:
> > > >> On Wed, Mar 04, 2026 at 10:47:50AM +0200, Leon Romanovsky wrote:
> > > >> > On Tue, Mar 03, 2026 at 04:15:20PM -0500, Peter Colberg wrote:
> > > >> > > Add Rust abstractions for the Single Root I/O Virtualization (SR-IOV)
> > > >> > > capability of a PCI device. Provide a minimal set of wrappers for the
> > > >> > > SR-IOV C API to enable and disable SR-IOV for a device, and query if
> > > >> > > a PCI device is a Physical Function (PF) or Virtual Function (VF).
> > > >> > 
> > > >> > <...>
> > > >> > 
> > > >> > > For PF drivers written in C, disabling SR-IOV on remove() may be opted
> > > >> > > into by setting the flag managed_sriov in the pci_driver structure. For
> > > >> > > PF drivers written in Rust, disabling SR-IOV on unbind() is mandatory.
> > > >> > 
> > > >> > Why? Could you explain the rationale behind this difference between C and
> > > >> > Rust? Let me remind you that SR‑IOV devices which do not disable VFs do so
> > > >> > for a practical and well‑established reason: maximizing hardware
> > > >> > utilization.
> > > >> 
> > > >> Personally I think drivers doing this are wrong. That such a driver
> > > >> bug was allowed to become UAPI is pretty bad. The rust approach is
> > > >> better.
> > > >
> > > > We already had this discussion. I see this as a perfectly valid
> > > > use-case.
> > > 
> > > Can you remind about a specific use-case for this please? (Ideally, one that
> > > can't be solved otherwise.)
> > 
> > You create X VFs through sriov_configure, unbind PF, bind it to vfio
> > instead and forward (X + 1) functions to different VMs.
> 
> No, illegal, and it doesn't even work right. When VFIO FLRs the PF it
> will blow up the half baked SRIOV and break everything.

The FLR can be disabled. For example, PCI_DEV_FLAGS_NO_FLR_RESET flag
will do it.

> 
> VFIO already has its own sriov_config support, the right flow is to
> bind the PF to VFIO and then enable sriov and do your assignments.

VFIO started to support SR-IOV in 137e5531351d ("vfio/pci: Add
sriov_configure support"), which was added 8 years after VFIO core was
added cba3345cc494 ("vfio: VFIO core").

Thanks

> 
> Jason
>