Re: [PATCH V3 10/10] vfio/pci: Clear VFIO_IRQ_INFO_NORESIZE for MSI-X

[Alex Williamson <alex.williamson@redhat.com>]

On Tue, 18 Apr 2023 10:29:21 -0700
Reinette Chatre <reinette.chatre@intel.com> wrote:

> Dynamic MSI-X is supported. Clear VFIO_IRQ_INFO_NORESIZE
> to provide guidance to user space.
> 
> Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
> ---
> Changes since V2:
> - Use new vdev->has_dyn_msix property instead of calling
>   pci_msix_can_alloc_dyn() directly. (Alex)
> 
> Changes since RFC V1:
> - Only advertise VFIO_IRQ_INFO_NORESIZE for MSI-X devices that
>   can actually support dynamic allocation. (Alex)
> 
>  drivers/vfio/pci/vfio_pci_core.c | 4 +++-
>  include/uapi/linux/vfio.h        | 3 +++
>  2 files changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> index a3635a8e54c8..4050ad3388c2 100644
> --- a/drivers/vfio/pci/vfio_pci_core.c
> +++ b/drivers/vfio/pci/vfio_pci_core.c
> @@ -1114,7 +1114,9 @@ static int vfio_pci_ioctl_get_irq_info(struct vfio_pci_core_device *vdev,
>  	if (info.index == VFIO_PCI_INTX_IRQ_INDEX)
>  		info.flags |=
>  			(VFIO_IRQ_INFO_MASKABLE | VFIO_IRQ_INFO_AUTOMASKED);
> -	else
> +	else if ((info.index != VFIO_PCI_MSIX_IRQ_INDEX) ||
> +		 (info.index == VFIO_PCI_MSIX_IRQ_INDEX &&
> +		  !vdev->has_dyn_msix))

Isn't this the same as:

	(info.index != VFIO_PCI_MSIX_IRQ_INDEX || !vdev->has_dyn_msix)

Thanks,
Alex

>  		info.flags |= VFIO_IRQ_INFO_NORESIZE;
>  
>  	return copy_to_user(arg, &info, minsz) ? -EFAULT : 0;
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index 0552e8dcf0cb..1a36134cae5c 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -511,6 +511,9 @@ struct vfio_region_info_cap_nvlink2_lnkspd {
>   * then add and unmask vectors, it's up to userspace to make the decision
>   * whether to allocate the maximum supported number of vectors or tear
>   * down setup and incrementally increase the vectors as each is enabled.
> + * Absence of the NORESIZE flag indicates that vectors can be enabled
> + * and disabled dynamically without impacting other vectors within the
> + * index.
>   */
>  struct vfio_irq_info {
>  	__u32	argsz;