Re: [PATCH v2 3/5] vfio-pci/zdev: define the vfio_zdev header

Alex Williamson
2020-10-02T21:44:29Z

On Fri, 2 Oct 2020 16:00:42 -0400
Matthew Rosato <mjrosato@linux.ibm.com> wrote:

> We define a new device region in vfio.h to be able to get the ZPCI CLP
> information by reading this region from userspace.
>
> We create a new file, vfio_zdev.h to define the structure of the new
> region defined in vfio.h
>
> Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
> ---
> include/uapi/linux/vfio.h | 5 ++
> include/uapi/linux/vfio_zdev.h | 118 +++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 123 insertions(+)
> create mode 100644 include/uapi/linux/vfio_zdev.h
>
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index 9204705..65eb367 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -326,6 +326,11 @@ struct vfio_region_info_cap_type {
> * to do TLB invalidation on a GPU.
> */
> #define VFIO_REGION_SUBTYPE_IBM_NVLINK2_ATSD (1)
> +/*
> + * IBM zPCI specific hardware feature information for a devcie. The contents
> + * of this region are mapped by struct vfio_region_zpci_info.
> + */
> +#define VFIO_REGION_SUBTYPE_IBM_ZPCI_CLP (2)
>
> /* sub-types for VFIO_REGION_TYPE_GFX */
> #define VFIO_REGION_SUBTYPE_GFX_EDID (1)
> diff --git a/include/uapi/linux/vfio_zdev.h b/include/uapi/linux/vfio_zdev.h
> new file mode 100644
> index 0000000..1c8fb62
> --- /dev/null
> +++ b/include/uapi/linux/vfio_zdev.h
> @@ -0,0 +1,118 @@
> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> +/*
> + * Region definition for ZPCI devices
> + *
> + * Copyright IBM Corp. 2020
> + *
> + * Author(s): Pierre Morel <pmorel@linux.ibm.com>
> + * Matthew Rosato <mjrosato@linux.ibm.com>
> + */
> +
> +#ifndef _VFIO_ZDEV_H_
> +#define _VFIO_ZDEV_H_
> +
> +#include <linux/types.h>
> +
> +/**
> + * struct vfio_region_zpci_info - ZPCI information
> + *
> + * This region provides zPCI specific hardware feature information for a
> + * device.
> + *
> + * The ZPCI information structure is presented as a chain of CLP features
> + * defined below. argsz provides the size of the entire region, and offset
> + * provides the location of the first CLP feature in the chain.
> + *
> + */
> +struct vfio_region_zpci_info {
> + __u32 argsz; /* Size of entire payload */
> + __u32 offset; /* Location of first entry */
> +};
> +
> +/**
> + * struct vfio_region_zpci_info_hdr - ZPCI header information
> + *
> + * This structure is included at the top of each CLP feature to define what
> + * type of CLP feature is presented / the structure version. The next value
> + * defines the offset of the next CLP feature, and is an offset from the very
> + * beginning of the region (vfio_region_zpci_info).
> + *
> + * Each CLP feature must have it's own unique 'id'.
> + */
> +struct vfio_region_zpci_info_hdr {
> + __u16 id; /* Identifies the CLP type */
> + __u16 version; /* version of the CLP data */
> + __u32 next; /* Offset of next entry */
> +};
> +
> +/**
> + * struct vfio_region_zpci_info_pci - Base PCI Function information
> + *
> + * This region provides a set of descriptive information about the associated
> + * PCI function.
> + */
> +#define VFIO_REGION_ZPCI_INFO_BASE 1
> +
> +struct vfio_region_zpci_info_base {
> + struct vfio_region_zpci_info_hdr hdr;
> + __u64 start_dma; /* Start of available DMA addresses */
> + __u64 end_dma; /* End of available DMA addresses */
> + __u16 pchid; /* Physical Channel ID */
> + __u16 vfn; /* Virtual function number */
> + __u16 fmb_length; /* Measurement Block Length (in bytes) */
> + __u8 pft; /* PCI Function Type */
> + __u8 gid; /* PCI function group ID */
> +};
> +
> +
> +/**
> + * struct vfio_region_zpci_info_group - Base PCI Function Group information
> + *
> + * This region provides a set of descriptive information about the group of PCI
> + * functions that the associated device belongs to.
> + */
> +#define VFIO_REGION_ZPCI_INFO_GROUP 2
> +
> +struct vfio_region_zpci_info_group {
> + struct vfio_region_zpci_info_hdr hdr;
> + __u64 dasm; /* DMA Address space mask */
> + __u64 msi_addr; /* MSI address */
> + __u64 flags;
> +#define VFIO_PCI_ZDEV_FLAGS_REFRESH 1 /* Use program-specified TLB refresh */
> + __u16 mui; /* Measurement Block Update Interval */
> + __u16 noi; /* Maximum number of MSIs */
> + __u16 maxstbl; /* Maximum Store Block Length */
> + __u8 version; /* Supported PCI Version */
> +};
> +
> +/**
> + * struct vfio_region_zpci_info_util - Utility String
> + *
> + * This region provides the utility string for the associated device, which is
> + * a device identifier string made up of EBCDID characters. 'size' specifies
> + * the length of 'util_str'.
> + */
> +#define VFIO_REGION_ZPCI_INFO_UTIL 3
> +
> +struct vfio_region_zpci_info_util {
> + struct vfio_region_zpci_info_hdr hdr;
> + __u32 size;
> + __u8 util_str[];
> +};
> +
> +/**
> + * struct vfio_region_zpci_info_pfip - PCI Function Path
> + *
> + * This region provides the PCI function path string, which is an identifier
> + * that describes the internal hardware path of the device. 'size' specifies
> + * the length of 'pfip'.
> + */
> +#define VFIO_REGION_ZPCI_INFO_PFIP 4
> +
> +struct vfio_region_zpci_info_pfip {
> +struct vfio_region_zpci_info_hdr hdr;
> + __u32 size;
> + __u8 pfip[];
> +};
> +
> +#endif

Can you discuss why a region with embedded capability chain is a better
solution than extending the VFIO_DEVICE_GET_INFO ioctl to support a
capability chain and providing this info there? This all appears to be
read-only info, so what's the benefit of duplicating yet another
capability chain in a region? It would also be possible to define four
separate device specific regions, one for each of these capabilities
rather than creating this chain. It just seems like a strange approach
TBH. Thanks,

Alex