linux-kernel - Re: [PATCH V3 08/10] vfio/pci: Probe and store ability to support dynamic MSI-X

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Date:   Tue, 18 Apr 2023 16:38:03 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Reinette Chatre <reinette.chatre@...el.com>
Cc:     jgg@...dia.com, yishaih@...dia.com,
        shameerali.kolothum.thodi@...wei.com, kevin.tian@...el.com,
        tglx@...utronix.de, darwi@...utronix.de, kvm@...r.kernel.org,
        dave.jiang@...el.com, jing2.liu@...el.com, ashok.raj@...el.com,
        fenghua.yu@...el.com, tom.zanussi@...ux.intel.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 08/10] vfio/pci: Probe and store ability to support
 dynamic MSI-X

On Tue, 18 Apr 2023 10:29:19 -0700
Reinette Chatre <reinette.chatre@...el.com> wrote:

> Not all MSI-X devices support dynamic MSI-X allocation. Whether
> a device supports dynamic MSI-X should be queried using
> pci_msix_can_alloc_dyn().
> 
> Instead of scattering code with pci_msix_can_alloc_dyn(),
> probe this ability once and store it as a property of the
> virtual device.
> 
> Suggested-by: Alex Williamson <alex.williamson@...hat.com>
> Signed-off-by: Reinette Chatre <reinette.chatre@...el.com>
> ---
> Changes since V2:
> - New patch. (Alex)
> 
>  drivers/vfio/pci/vfio_pci_core.c | 5 ++++-
>  include/linux/vfio_pci_core.h    | 1 +
>  2 files changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> index ae0e161c7fc9..a3635a8e54c8 100644
> --- a/drivers/vfio/pci/vfio_pci_core.c
> +++ b/drivers/vfio/pci/vfio_pci_core.c
> @@ -530,8 +530,11 @@ int vfio_pci_core_enable(struct vfio_pci_core_device *vdev)
>  		vdev->msix_bar = table & PCI_MSIX_TABLE_BIR;
>  		vdev->msix_offset = table & PCI_MSIX_TABLE_OFFSET;
>  		vdev->msix_size = ((flags & PCI_MSIX_FLAGS_QSIZE) + 1) * 16;
> -	} else
> +		vdev->has_dyn_msix = pci_msix_can_alloc_dyn(pdev);
> +	} else {
>  		vdev->msix_bar = 0xFF;
> +		vdev->has_dyn_msix = false;
> +	}
>  
>  	if (!vfio_vga_disabled() && vfio_pci_is_vga(pdev))
>  		vdev->has_vga = true;
> diff --git a/include/linux/vfio_pci_core.h b/include/linux/vfio_pci_core.h
> index 148fd1ae6c1c..4f070f2d6fde 100644
> --- a/include/linux/vfio_pci_core.h
> +++ b/include/linux/vfio_pci_core.h
> @@ -67,6 +67,7 @@ struct vfio_pci_core_device {
>  	u8			msix_bar;
>  	u16			msix_size;
>  	u32			msix_offset;
> +	bool			has_dyn_msix;
>  	u32			rbar[7];
>  	bool			pci_2_3;
>  	bool			virq_disabled;

Nit, the whole data structure probably needs to be sorted with pahole,
but creating a hole here for locality to other msix fields should
probably be secondary to keeping the structure well packed, which
suggests including this new field among the bools below.  Thanks,

Alex