linux-kernel - Re: [PATCH v9 19/21] vfio-pci/zdev: different maxstbl for interpreted devices

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Date:   Tue, 28 Jun 2022 09:00:19 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Matthew Rosato <mjrosato@...ux.ibm.com>
Cc:     linux-s390@...r.kernel.org, cohuck@...hat.com,
        schnelle@...ux.ibm.com, farman@...ux.ibm.com, pmorel@...ux.ibm.com,
        borntraeger@...ux.ibm.com, hca@...ux.ibm.com, gor@...ux.ibm.com,
        gerald.schaefer@...ux.ibm.com, agordeev@...ux.ibm.com,
        svens@...ux.ibm.com, frankja@...ux.ibm.com, david@...hat.com,
        imbrenda@...ux.ibm.com, vneethv@...ux.ibm.com,
        oberpar@...ux.ibm.com, freude@...ux.ibm.com, thuth@...hat.com,
        pasic@...ux.ibm.com, pbonzini@...hat.com, corbet@....net,
        jgg@...dia.com, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v9 19/21] vfio-pci/zdev: different maxstbl for
 interpreted devices

On Mon,  6 Jun 2022 16:33:23 -0400
Matthew Rosato <mjrosato@...ux.ibm.com> wrote:

> When doing load/store interpretation, the maximum store block length is
> determined by the underlying firmware, not the host kernel API.  Reflect
> that in the associated Query PCI Function Group clp capability and let
> userspace decide which is appropriate to present to the guest.
> 
> Reviewed-by: Pierre Morel <pmorel@...ux.ibm.com>
> Signed-off-by: Matthew Rosato <mjrosato@...ux.ibm.com>
> ---
>  drivers/vfio/pci/vfio_pci_zdev.c | 6 ++++--
>  include/uapi/linux/vfio_zdev.h   | 4 ++++
>  2 files changed, 8 insertions(+), 2 deletions(-)


Acked-by: Alex Williamson <alex.williamson@...hat.com>


> diff --git a/drivers/vfio/pci/vfio_pci_zdev.c b/drivers/vfio/pci/vfio_pci_zdev.c
> index 4f28cdd7ecd1..e163aa9f6144 100644
> --- a/drivers/vfio/pci/vfio_pci_zdev.c
> +++ b/drivers/vfio/pci/vfio_pci_zdev.c
> @@ -45,14 +45,16 @@ static int zpci_group_cap(struct zpci_dev *zdev, struct vfio_info_cap *caps)
>  {
>  	struct vfio_device_info_cap_zpci_group cap = {
>  		.header.id = VFIO_DEVICE_INFO_CAP_ZPCI_GROUP,
> -		.header.version = 1,
> +		.header.version = 2,
>  		.dasm = zdev->dma_mask,
>  		.msi_addr = zdev->msi_addr,
>  		.flags = VFIO_DEVICE_INFO_ZPCI_FLAG_REFRESH,
>  		.mui = zdev->fmb_update,
>  		.noi = zdev->max_msi,
>  		.maxstbl = ZPCI_MAX_WRITE_SIZE,
> -		.version = zdev->version
> +		.version = zdev->version,
> +		.reserved = 0,
> +		.imaxstbl = zdev->maxstbl
>  	};
>  
>  	return vfio_info_add_capability(caps, &cap.header, sizeof(cap));
> diff --git a/include/uapi/linux/vfio_zdev.h b/include/uapi/linux/vfio_zdev.h
> index 78c022af3d29..77f2aff1f27e 100644
> --- a/include/uapi/linux/vfio_zdev.h
> +++ b/include/uapi/linux/vfio_zdev.h
> @@ -50,6 +50,10 @@ struct vfio_device_info_cap_zpci_group {
>  	__u16 noi;		/* Maximum number of MSIs */
>  	__u16 maxstbl;		/* Maximum Store Block Length */
>  	__u8 version;		/* Supported PCI Version */
> +	/* End of version 1 */
> +	__u8 reserved;
> +	__u16 imaxstbl;		/* Maximum Interpreted Store Block Length */
> +	/* End of version 2 */
>  };
>  
>  /**