linux-kernel - Re: [PATCH 30/32] vfio-pci/zdev: add DTSM to clp group capability

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Message-ID: <b54b2ee9-3d7f-11b7-9aa4-e5dafd01a086@linux.ibm.com>
Date:   Tue, 14 Dec 2021 10:58:21 +0100
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Matthew Rosato <mjrosato@...ux.ibm.com>, linux-s390@...r.kernel.org
Cc:     alex.williamson@...hat.com, cohuck@...hat.com,
        schnelle@...ux.ibm.com, farman@...ux.ibm.com,
        borntraeger@...ux.ibm.com, hca@...ux.ibm.com, gor@...ux.ibm.com,
        gerald.schaefer@...ux.ibm.com, agordeev@...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, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 30/32] vfio-pci/zdev: add DTSM to clp group capability



On 12/7/21 21:57, Matthew Rosato wrote:
> The DTSM, or designation type supported mask, indicates what IOAT formats
> are available to the guest.  For an interpreted device, userspace will not
> know what format(s) the IOAT assist supports, so pass it via the
> capability chain.  Since the value belongs to the Query PCI Function Group
> clp, let's extend the existing capability with a new version.
> 
> Signed-off-by: Matthew Rosato <mjrosato@...ux.ibm.com>
> ---
>   drivers/vfio/pci/vfio_pci_zdev.c | 9 ++++++---
>   include/uapi/linux/vfio_zdev.h   | 3 +++
>   2 files changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/vfio/pci/vfio_pci_zdev.c b/drivers/vfio/pci/vfio_pci_zdev.c
> index 85be77492a6d..342b59ed36c9 100644
> --- a/drivers/vfio/pci/vfio_pci_zdev.c
> +++ b/drivers/vfio/pci/vfio_pci_zdev.c
> @@ -45,19 +45,22 @@ 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,

This, maxstbl, is not part of the patch but shouldn't we consider it too?
The maxstbl is fixed for intercepted VFIO because the kernel is handling 
the STBL instruction in behalf of the guest.
Here the guest will use STBL directly.

I think we should report the right maxstbl value.

> -		.version = zdev->version
> +		.version = zdev->version,
> +		.dtsm = 0
>   	};
>   
>   	/* Some values are different for interpreted devices */
> -	if (zdev->kzdev && zdev->kzdev->interp)
> +	if (zdev->kzdev && zdev->kzdev->interp) {
>   		cap.maxstbl = zdev->maxstbl;
> +		cap.dtsm = kvm_s390_pci_get_dtsm(zdev);
> +	}
>   
>   	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 1a5229b7bb18..b4c2ba8e71f0 100644
> --- a/include/uapi/linux/vfio_zdev.h
> +++ b/include/uapi/linux/vfio_zdev.h
> @@ -47,6 +47,9 @@ 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 dtsm;		/* Supported IOAT Designations */
> +	/* End of version 2 */
>   };
>   
>   /**
> 

-- 
Pierre Morel
IBM Lab Boeblingen