Re: VFIO support on hyperv (vfio_pci_core_ioctl())

[Alex Williamson <alex@shazbot.org>]

On Wed, 25 Feb 2026 14:04:49 -0800
Mukesh R <mrathor@linux.microsoft.com> wrote:

> Hi Alex et al:
> 
> I've been looking at making pci passthru irq setup/remap work on hyperv
> for the latest (6.19) version using vfio core. Unfortunately, it's just
> not fitting well because in case of hyperv the irq remap is done by
> the hypervisor. Specifically, for a robust and proper solution, we need
> to override vfio_pci_set_msi_trigger(). As such, for the best way forward
> I am trying to figure how much flexibility there is to modify
> vfio_pci_intrs.c with "if (running_on_hyperv())" branches (putting hyperv
> code in separate file).
> 
> If none, then the alternative would be to create vfio-hyperv.c with
> vfio_device_ops.ioctl = hyperv_vfio_pci_core_ioctl(). But, then I'd
> be replicating code for other sub ioctls like vfio_pci_ioctl_get_info(),
> vfio_pci_ioctl_get_irq_info(), etc. Would it be acceptable to make them
> non static in this case?
> 
> Please let me know your thoughts or if you have other suggestions.

Hi Mukesh,

In general, littering the code with running_on_hyperv() tests is not
acceptable, but the presented alternative isn't really accurate either.
If you want to substitute in your own ioctl callback, you can still
call vfio_pci_core_ioctl() for all the unhandled ioctls, without extra
exports.  We can also look at whether vfio_pci_device_ops could have a
callback specifically addressing an alternative set_msi_trigger
handler.  Thanks,

Alex