Subject: Re: [PATCH v6 3/4] ndctl/papr_scm, uapi: Add support for PAPR nvdimm specific methods

From: Michael Ellerman <[email-masked]>
Date: Thu, 30 Apr 2020 19:17:38 +1000

Vaibhav Jain <[email-masked]> writes:
> Introduce support for Papr nvDimm Specific Methods (PDSM) in papr_scm
> modules and add the command family to the white list of NVDIMM command
> sets. Also advertise support for ND_CMD_CALL for the dimm
> command mask and implement necessary scaffolding in the module to
> handle ND_CMD_CALL ioctl and PDSM requests that we receive.
>
> The layout of the PDSM request as we expect from libnvdimm/libndctl is
> described in newly introduced uapi header 'papr_scm_pdsm.h' which
> defines a new 'struct nd_pdsm_cmd_pkg' header. This header is used
> to communicate the PDSM request via member
> 'nd_pkg_papr_scm->nd_command' and size of payload that need to be
> sent/received for servicing the PDSM.
>
> A new function is_cmd_valid() is implemented that reads the args to
> papr_scm_ndctl() and performs sanity tests on them. A new function
> papr_scm_service_pdsm() is introduced and is called from
> papr_scm_ndctl() in case of a PDSM request is received via ND_CMD_CALL
> command from libnvdimm.
>
> Cc: Dan Williams <[email-masked]>
> Cc: Michael Ellerman <[email-masked]>
> Cc: "Aneesh Kumar K . V" <[email-masked]>
> Signed-off-by: Vaibhav Jain <[email-masked]>
> ---
> Changelog
>
> v5..v6 :
> * Changed the usage of the term DSM to PDSM to distinguish it from the
>   ACPI term [ Dan Williams ]
> * Renamed papr_scm_dsm.h to papr_scm_pdsm.h and updated various struct
>   to reflect the new terminology.
> * Updated the patch description and title to reflect the new terminology.
> * Squashed patch to introduce new command family in 'ndctl.h' with
>   this patch [ Dan Williams ]
> * Updated the papr_scm_pdsm method starting index from 0x10000 to 0x0
>   [ Dan Williams ]
> * Removed redundant license text from the papr_scm_psdm.h file.
>   [ Dan Williams ]
> * s/envelop/envelope/ at various places [ Dan Williams ]
> * Added '__packed' attribute to command package header to gaurd
>   against different compiler adding paddings between the fields.
>   [ Dan Williams]
> * Converted various pr_debug to dev_debug [ Dan Williams ]
>
> v4..v5 :
> * None
>
> v3..v4 :
> * None
>
> v2..v3 :
> * Updated the patch prefix to 'ndctl/uapi' [Aneesh]
>
> v1..v2 :
> * None
> ---
>  arch/powerpc/include/uapi/asm/papr_scm_pdsm.h | 153 ++++++++++++++++++
>  arch/powerpc/platforms/pseries/papr_scm.c     | 101 +++++++++++-
>  include/uapi/linux/ndctl.h                    |   1 +
>  3 files changed, 249 insertions(+), 6 deletions(-)
>  create mode 100644 arch/powerpc/include/uapi/asm/papr_scm_pdsm.h
>
> diff --git a/arch/powerpc/include/uapi/asm/papr_scm_pdsm.h b/arch/powerpc/include/uapi/asm/papr_scm_pdsm.h
> new file mode 100644
> index 000000000000..ec48b5c7fc18
> --- /dev/null
> +++ b/arch/powerpc/include/uapi/asm/papr_scm_pdsm.h
> @@ -0,0 +1,153 @@
> +/* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
> +/*
> + * PAPR-SCM Dimm specific methods (PDSM) and structs for libndctl
> + *
> + * (C) Copyright IBM 2020
> + *
> + * Author: Vaibhav Jain <vaibhav at linux.ibm.com>
> + */
> +
> +#ifndef _UAPI_ASM_POWERPC_PAPR_SCM_PDSM_H_
> +#define _UAPI_ASM_POWERPC_PAPR_SCM_PDSM_H_
> +
> +#include <linux/types.h>
> +
> +#ifdef __KERNEL__
> +#include <linux/ndctl.h>
> +#else
> +#include <ndctl.h>
> +#endif

We shouldn't be checking __KERNEL__ in uapi headers, something has gone
wrong if this is necessary.

> +
> +/*
> + * PDSM Envelope:
> + *
> + * The ioctl ND_CMD_CALL transfers data between user-space and kernel via
> + * 'envelopes' which consists of a header and user-defined payload sections.
> + * The header is described by 'struct nd_pdsm_cmd_pkg' which expects a
> + * payload following it and offset of which relative to the struct is provided
> + * by 'nd_pdsm_cmd_pkg.payload_offset'. *
> + *
> + *  +-------------+---------------------+---------------------------+
> + *  |   64-Bytes  |       8-Bytes       |       Max 184-Bytes       |
> + *  +-------------+---------------------+---------------------------+
> + *  |               nd_pdsm_cmd_pkg |                           |
> + *  |-------------+                     |                           |
> + *  |  nd_cmd_pkg |                     |                           |
> + *  +-------------+---------------------+---------------------------+
> + *  | nd_family   |			|			    |
> + *  | nd_size_out | cmd_status          |			    |
> + *  | nd_size_in  | payload_version     |      PAYLOAD		    |
> + *  | nd_command  | payload_offset ----->			    |
> + *  | nd_fw_size  |                     |			    |
> + *  +-------------+---------------------+---------------------------+
> + *
> + * PDSM Header:
> + *
> + * The header is defined as 'struct nd_pdsm_cmd_pkg' which embeds a
> + * 'struct nd_cmd_pkg' instance. The PDSM command is assigned to member
> + * 'nd_cmd_pkg.nd_command'. Apart from size information of the envelope which is
> + * contained in 'struct nd_cmd_pkg', the header also has members following
> + * members:
> + *
> + * 'cmd_status'		: (Out) Errors if any encountered while servicing PDSM.
> + * 'payload_version'	: (In/Out) Version number associated with the payload.
> + * 'payload_offset'	: (In)Relative offset of payload from start of envelope.
> + *
> + * PDSM Payload:
> + *
> + * The layout of the PDSM Payload is defined by various structs shared between
> + * papr_scm and libndctl so that contents of payload can be interpreted. During
> + * servicing of a PDSM the papr_scm module will read input args from the payload
> + * field by casting its contents to an appropriate struct pointer based on the
> + * PDSM command. Similarly the output of servicing the PDSM command will be
> + * copied to the payload field using the same struct.
> + *
> + * 'libnvdimm' enforces a hard limit of 256 bytes on the envelope size, which
> + * leaves around 184 bytes for the envelope payload (ignoring any padding that
> + * the compiler may silently introduce).
> + *
> + * Payload Version:
> + *
> + * A 'payload_version' field is present in PDSM header that indicates a specific
> + * version of the structure present in PDSM Payload for a given PDSM command.
> + * This provides backward compatibility in case the PDSM Payload structure
> + * evolves and different structures are supported by 'papr_scm' and 'libndctl'.
> + *
> + * When sending a PDSM Payload to 'papr_scm', 'libndctl' should send the version
> + * of the payload struct it supports via 'payload_version' field. The 'papr_scm'
> + * module when servicing the PDSM envelope checks the 'payload_version' and then
> + * uses 'payload struct version' == MIN('payload_version field',
> + * 'max payload-struct-version supported by papr_scm') to service the PDSM.
> + * After servicing the PDSM, 'papr_scm' put the negotiated version of payload
> + * struct in returned 'payload_version' field.
> + *
> + * Libndctl on receiving the envelope back from papr_scm again checks the
> + * 'payload_version' field and based on it use the appropriate version dsm
> + * struct to parse the results.
> + *
> + * Backward Compatibility:
> + *
> + * Above scheme of exchanging different versioned PDSM struct between libndctl
> + * and papr_scm should provide backward compatibility until following two
> + * assumptions/conditions when defining new PDSM structs hold:
> + *
> + * Let T(X) = { set of attributes in PDSM struct 'T' versioned X }
> + *
> + * 1. T(X) is a proper subset of T(Y) if X > Y.
> + *    i.e Each new version of PDSM struct should retain existing struct
> + *    attributes from previous version
> + *
> + * 2. If an entity (libndctl or papr_scm) supports a PDSM struct T(X) then
> + *    it should also support T(1), T(2)...T(X - 1).
> + *    i.e When adding support for new version of a PDSM struct, libndctl
> + *    and papr_scm should retain support of the existing PDSM struct
> + *    version they support.
> + */
> +
> +#ifndef __packed
> +#define __packed __attribute__((packed))
> +#endif

I'm not sure it's kosher to be defining __packed in a uapi header.

> +
> +/* Papr-scm-header + payload expected with ND_CMD_CALL ioctl from libnvdimm */
> +struct nd_pdsm_cmd_pkg {
> +	struct nd_cmd_pkg hdr;	/* Package header containing sub-cmd */
> +	__s32 cmd_status;	/* Out: Sub-cmd status returned back */
> +	__u16 payload_offset;	/* In: offset from start of struct */
> +	__u16 payload_version;	/* In/Out: version of the payload */
> +	__u8 payload[];		/* In/Out: Sub-cmd data buffer */
> +} __packed;
> +
> +/*
> + * Methods to be embedded in ND_CMD_CALL request. These are sent to the kernel
> + * via 'nd_pdsm_cmd_pkg.hdr.nd_command' member of the ioctl struct
> + */
> +enum papr_scm_pdsm {
> +	PAPR_SCM_PDSM_MIN = 0x0,
> +	PAPR_SCM_PDSM_MAX,
> +};
> +
> +/* Helpers to evaluate the size of PDSM envelope */
> +/* Calculate the papr_scm-header size */
> +#define ND_PDSM_ENVELOPE_CONTENT_HDR_SIZE \
> +	(sizeof(struct nd_pdsm_cmd_pkg) - sizeof(struct nd_cmd_pkg))
> +
> +/* Given a type calculate envelope-content size (papr_scm-header + payload) */
> +#define ND_PDSM_ENVELOPE_CONTENT_SIZE(_type_)	\
> +	(sizeof(_type_) + ND_PDSM_ENVELOPE_CONTENT_HDR_SIZE)

Those seem unused? Do we really need to make them part of the uapi for
all time?

> +/* Convert a libnvdimm nd_cmd_pkg to pdsm specific pkg */
> +static struct nd_pdsm_cmd_pkg *nd_to_pdsm_cmd_pkg(struct nd_cmd_pkg *cmd)
> +{
> +	return (struct nd_pdsm_cmd_pkg *) cmd;
> +}
> +
> +/* Return the payload pointer for a given pcmd */
> +static void *pdsm_cmd_to_payload(struct nd_pdsm_cmd_pkg *pcmd)

That should probably be static inline?

> +{
> +	if (pcmd->hdr.nd_size_in == 0 && pcmd->hdr.nd_size_out == 0)
> +		return NULL;
> +	else
> +		return (void *)((__u8 *) pcmd + pcmd->payload_offset);
> +}
> +
> +#endif /* _UAPI_ASM_POWERPC_PAPR_SCM_PDSM_H_ */
> diff --git a/arch/powerpc/platforms/pseries/papr_scm.c b/arch/powerpc/platforms/pseries/papr_scm.c
> index f8fe579e6f2e..20da1b837017 100644
> --- a/arch/powerpc/platforms/pseries/papr_scm.c
> +++ b/arch/powerpc/platforms/pseries/papr_scm.c
> @@ -15,13 +15,15 @@
>  
>  #include <asm/plpar_wrappers.h>
>  #include <asm/papr_scm.h>
> +#include <asm/papr_scm_pdsm.h>
>  
>  #define BIND_ANY_ADDR (~0ul)
>  
>  #define PAPR_SCM_DIMM_CMD_MASK \
>  	((1ul << ND_CMD_GET_CONFIG_SIZE) | \
>  	 (1ul << ND_CMD_GET_CONFIG_DATA) | \
> -	 (1ul << ND_CMD_SET_CONFIG_DATA))
> +	 (1ul << ND_CMD_SET_CONFIG_DATA) | \
> +	 (1ul << ND_CMD_CALL))
>  
>  struct papr_scm_priv {
>  	struct platform_device *pdev;
> @@ -306,16 +308,97 @@ static int papr_scm_meta_set(struct papr_scm_priv *p,
>  	return 0;
>  }
>  
> -int papr_scm_ndctl(struct nvdimm_bus_descriptor *nd_desc, struct nvdimm *nvdimm,
> -		unsigned int cmd, void *buf, unsigned int buf_len, int *cmd_rc)
> +/*
> + * Validate the inputs args to dimm-control function and return '0' if valid.
> + * This also does initial sanity validation to ND_CMD_CALL sub-command packages.
> + */
> +static int is_cmd_valid(struct nvdimm *nvdimm, unsigned int cmd, void *buf,
> +		       unsigned int buf_len)
>  {
> -	struct nd_cmd_get_config_size *get_size_hdr;
> +	unsigned long cmd_mask = PAPR_SCM_DIMM_CMD_MASK;
> +	struct nd_pdsm_cmd_pkg *pkg = nd_to_pdsm_cmd_pkg(buf);
>  	struct papr_scm_priv *p;
>  
>  	/* Only dimm-specific calls are supported atm */
>  	if (!nvdimm)
>  		return -EINVAL;
>  
> +	/* get the provider date from struct nvdimm */
> +	p = nvdimm_provider_data(nvdimm);
> +
> +	if (!test_bit(cmd, &cmd_mask)) {
> +		dev_dbg(&p->pdev->dev, "Unsupported cmd=%u\n", cmd);
> +		return -EINVAL;
> +	} else if (cmd == ND_CMD_CALL) {
> +
> +		/* Verify the envelope package */
> +		if (!buf || buf_len < sizeof(struct nd_pdsm_cmd_pkg)) {
> +			dev_dbg(&p->pdev->dev, "Invalid pkg size=%u\n",
> +				buf_len);
> +			return -EINVAL;
> +		}
> +
> +		/* Verify that the PDSM family is valid */
> +		if (pkg->hdr.nd_family != NVDIMM_FAMILY_PAPR_SCM) {
> +			dev_dbg(&p->pdev->dev, "Invalid pkg family=0x%llx\n",
> +				pkg->hdr.nd_family);
> +			return -EINVAL;
> +
> +		}
> +
> +		/* We except a payload with all PDSM commands */
> +		if (pdsm_cmd_to_payload(pkg) == NULL) {
> +			dev_dbg(&p->pdev->dev,
> +				"Empty payload for sub-command=0x%llx\n",
> +				pkg->hdr.nd_command);
> +			return -EINVAL;
> +		}
> +	}
> +
> +	/* Command looks valid */
> +	return 0;
> +}
> +
> +static int papr_scm_service_pdsm(struct papr_scm_priv *p,
> +				struct nd_pdsm_cmd_pkg *call_pkg)
> +{
> +	/* unknown subcommands return error in packages */
> +	if (call_pkg->hdr.nd_command <= PAPR_SCM_PDSM_MIN ||
> +	    call_pkg->hdr.nd_command >= PAPR_SCM_PDSM_MAX) {
> +		dev_dbg(&p->pdev->dev, "Invalid PDSM request 0x%llx\n",
> +			call_pkg->hdr.nd_command);
> +		call_pkg->cmd_status = -EINVAL;
> +		return 0;
> +	}
> +
> +	/* Depending on the DSM command call appropriate service routine */
> +	switch (call_pkg->hdr.nd_command) {
> +	default:
> +		dev_dbg(&p->pdev->dev, "Unsupported PDSM request 0x%llx\n",
> +			call_pkg->hdr.nd_command);
> +		call_pkg->cmd_status = -ENOENT;
> +		return 0;
> +	}
> +}
> +
> +int papr_scm_ndctl(struct nvdimm_bus_descriptor *nd_desc, struct nvdimm *nvdimm,
> +		unsigned int cmd, void *buf, unsigned int buf_len, int *cmd_rc)
> +{
> +	struct nd_cmd_get_config_size *get_size_hdr;
> +	struct papr_scm_priv *p;
> +	struct nd_pdsm_cmd_pkg *call_pkg = NULL;
> +	int rc;
> +
> +	/* Use a local variable in case cmd_rc pointer is NULL */
> +	if (cmd_rc == NULL)
> +		cmd_rc = &rc;
> +
> +	*cmd_rc = is_cmd_valid(nvdimm, cmd, buf, buf_len);
> +	if (*cmd_rc) {
> +		pr_debug("Invalid cmd=0x%x. Err=%d\n", cmd, *cmd_rc);
> +		return *cmd_rc;
> +	}
> +
>  	p = nvdimm_provider_data(nvdimm);
>  
>  	switch (cmd) {
> @@ -336,13 +419,19 @@ int papr_scm_ndctl(struct nvdimm_bus_descriptor *nd_desc, struct nvdimm *nvdimm,
>  		*cmd_rc = papr_scm_meta_set(p, buf);
>  		break;
>  
> +	case ND_CMD_CALL:
> +		call_pkg = nd_to_pdsm_cmd_pkg(buf);
> +		*cmd_rc = papr_scm_service_pdsm(p, call_pkg);
> +		break;
> +
>  	default:
> -		return -EINVAL;
> +		dev_dbg(&p->pdev->dev, "Unknown command = %d\n", cmd);
> +		*cmd_rc = -EINVAL;
>  	}
>  
>  	dev_dbg(&p->pdev->dev, "returned with cmd_rc = %d\n", *cmd_rc);
>  
> -	return 0;
> +	return *cmd_rc;
>  }
>  
>  static inline int papr_scm_node(int node)
> diff --git a/include/uapi/linux/ndctl.h b/include/uapi/linux/ndctl.h
> index de5d90212409..99fb60600ef8 100644
> --- a/include/uapi/linux/ndctl.h
> +++ b/include/uapi/linux/ndctl.h
> @@ -244,6 +244,7 @@ struct nd_cmd_pkg {
>  #define NVDIMM_FAMILY_HPE2 2
>  #define NVDIMM_FAMILY_MSFT 3
>  #define NVDIMM_FAMILY_HYPERV 4
> +#define NVDIMM_FAMILY_PAPR_SCM 5

Would like an ack from Dan for that change.

cheers