Re: [PATCH v5 3/4] powerpc/papr_scm,uapi: Add support for handling PAPR DSM commands

["Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>]

Vaibhav Jain <vaibhav@linux.ibm.com> writes:

> Implement support for handling PAPR DSM commands in papr_scm
> module. We 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 DSM commands that we receive.
>
> The layout of the DSM commands as we expect from libnvdimm/libndctl is
> described in newly introduced uapi header 'papr_scm_dsm.h' which
> defines a new 'struct nd_papr_scm_cmd_pkg' header. This header is used
> to communicate the DSM command via 'nd_pkg_papr_scm->nd_command' and
> size of payload that need to be sent/received for servicing the DSM.
>
> The PAPR DSM commands are assigned indexes started from 0x10000 to
> prevent them from overlapping ND_CMD_* values and also makes handling
> dimm commands in papr_scm_ndctl(). A new function cmd_to_func() is
> implemented that reads the args to papr_scm_ndctl() and performs
> sanity tests on them. In case of a DSM command being sent via
> ND_CMD_CALL a newly introduced function papr_scm_service_dsm() is
> called to handle the request.
>

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>

> Signed-off-by: Vaibhav Jain <vaibhav@linux.ibm.com>
>
> ---
> Changelog:
>
> v4..v5: Fixed a bug in new implementation of papr_scm_ndctl().
>
> v3..v4: Updated papr_scm_ndctl() to delegate DSM command handling to a
> 	different function papr_scm_service_dsm(). [Aneesh]
>
> v2..v3: Updated the nd_papr_scm_cmd_pkg to use __xx types as its
> 	exported to the userspace [Aneesh]
>
> v1..v2: New patch in the series.
> ---
>  arch/powerpc/include/uapi/asm/papr_scm_dsm.h | 161 +++++++++++++++++++
>  arch/powerpc/platforms/pseries/papr_scm.c    |  97 ++++++++++-
>  2 files changed, 252 insertions(+), 6 deletions(-)
>  create mode 100644 arch/powerpc/include/uapi/asm/papr_scm_dsm.h
>
> diff --git a/arch/powerpc/include/uapi/asm/papr_scm_dsm.h b/arch/powerpc/include/uapi/asm/papr_scm_dsm.h
> new file mode 100644
> index 000000000000..c039a49b41b4
> --- /dev/null
> +++ b/arch/powerpc/include/uapi/asm/papr_scm_dsm.h
> @@ -0,0 +1,161 @@
> +/* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
> +/*
> + * PAPR SCM Device specific methods and struct for libndctl and ndctl
> + *
> + * (C) Copyright IBM 2020
> + *
> + * Author: Vaibhav Jain <vaibhav at linux.ibm.com>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2, or (at your option)
> + * any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + */
> +
> +#ifndef _UAPI_ASM_POWERPC_PAPR_SCM_DSM_H_
> +#define _UAPI_ASM_POWERPC_PAPR_SCM_DSM_H_
> +
> +#include <linux/types.h>
> +
> +#ifdef __KERNEL__
> +#include <linux/ndctl.h>
> +#else
> +#include <ndctl.h>
> +#endif
> +
> +/*
> + * DSM 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_papr_scm_cmd_pkg' which expects a
> + * payload following it and offset of which relative to the struct is provided
> + * by 'nd_papr_scm_cmd_pkg.payload_offset'. *
> + *
> + *  +-------------+---------------------+---------------------------+
> + *  |   64-Bytes  |       8-Bytes       |       Max 184-Bytes       |
> + *  +-------------+---------------------+---------------------------+
> + *  |               nd_papr_scm_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  |                     |			    |
> + *  +-------------+---------------------+---------------------------+
> + *
> + * DSM Header:
> + *
> + * The header is defined as 'struct nd_papr_scm_cmd_pkg' which embeds a
> + * 'struct nd_cmd_pkg' instance. The DSM command is assigned to member
> + * 'nd_cmd_pkg.nd_command'. Apart from size information of the envelop which is
> + * contained in 'struct nd_cmd_pkg', the header also has members following
> + * members:
> + *
> + * 'cmd_status'		: (Out) Errors if any encountered while servicing DSM.
> + * 'payload_version'	: (In/Out) Version number associated with the payload.
> + * 'payload_offset'	: (In)Relative offset of payload from start of envelope.
> + *
> + * DSM Payload:
> + *
> + * The layout of the DSM Payload is defined by various structs shared between
> + * papr_scm and libndctl so that contents of payload can be interpreted. During
> + * servicing of a DSM the papr_scm module will read input args from the payload
> + * field by casting its contents to an appropriate struct pointer based on the
> + * DSM command. Similarly the output of servicing the DSM 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 DSM header that indicates a specific
> + * version of the structure present in DSM Payload for a given DSM command. This
> + * provides backward compatibility in case the DSM Payload structure evolves
> + * and different structures are supported by 'papr_scm' and 'libndctl'.
> + *
> + * When sending a DSM 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 DSM envelop 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 DSM. After
> + * servicing the DSM, 'papr_scm' put the negotiated version of payload struct in
> + * returned 'payload_version' field.
> + *
> + * Libndctl on receiving the envelop 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 DSM struct between libndctl
> + * and papr_scm should provide backward compatibility until following two
> + * assumptions/conditions when defining new DSM structs hold:
> + *
> + * Let T(X) = { set of attributes in DSM struct 'T' versioned X }
> + *
> + * 1. T(X) is a proper subset of T(Y) if X > Y.
> + *    i.e Each new version of DSM struct should retain existing struct
> + *    attributes from previous version
> + *
> + * 2. If an entity (libndctl or papr_scm) supports a DSM 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 DSM struct, libndctl
> + *    and papr_scm should retain support of the existing DSM struct
> + *    version they support.
> + */
> +
> +/* Papr-scm-header + payload expected with ND_CMD_CALL ioctl from libnvdimm */
> +struct nd_papr_scm_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 */
> +};
> +
> +/*
> + * Sub commands for ND_CMD_CALL. To prevent overlap from ND_CMD_*, values for
> + * these enums start at 0x10000. These values are then returned from
> + * cmd_to_func() making it easy to implement the switch-case block in
> + * papr_scm_ndctl(). These commands are sent to the kernel via
> + * 'nd_papr_scm_cmd_pkg.hdr.nd_command'
> + */
> +enum dsm_papr_scm {
> +	DSM_PAPR_SCM_MIN =  0x10000,
> +	DSM_PAPR_SCM_MAX,
> +};
> +
> +/* Helpers to evaluate the size of PAPR_SCM envelope */
> +/* Calculate the papr_scm-header size */
> +#define ND_PAPR_SCM_ENVELOPE_CONTENT_HDR_SIZE \
> +	(sizeof(struct nd_papr_scm_cmd_pkg) - sizeof(struct nd_cmd_pkg))
> +
> +/* Given a type calculate envelope-content size (papr_scm-header + payload) */
> +#define ND_PAPR_SCM_ENVELOPE_CONTENT_SIZE(_type_)	\
> +	(sizeof(_type_) + ND_PAPR_SCM_ENVELOPE_CONTENT_HDR_SIZE)
> +
> +/* Convert a libnvdimm nd_cmd_pkg to papr_scm specific pkg */
> +static struct nd_papr_scm_cmd_pkg *nd_to_papr_cmd_pkg(struct nd_cmd_pkg *cmd)
> +{
> +	return (struct nd_papr_scm_cmd_pkg *) cmd;
> +}
> +
> +/* Return the payload pointer for a given pcmd */
> +static void *papr_scm_pcmd_to_payload(struct nd_papr_scm_cmd_pkg *pcmd)
> +{
> +	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_DSM_H_ */
> diff --git a/arch/powerpc/platforms/pseries/papr_scm.c b/arch/powerpc/platforms/pseries/papr_scm.c
> index aaf2e4ab1f75..e8ce96d2249e 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_dsm.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;
> @@ -283,15 +285,92 @@ static int papr_scm_meta_set(struct papr_scm_priv *p,
>  	return 0;
>  }
>  
> +/*
> + * 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)
> +{
> +	unsigned long cmd_mask = PAPR_SCM_DIMM_CMD_MASK;
> +	struct nd_papr_scm_cmd_pkg *pkg = nd_to_papr_cmd_pkg(buf);
> +
> +	/* Only dimm-specific calls are supported atm */
> +	if (!nvdimm)
> +		return -EINVAL;
> +
> +	if (!test_bit(cmd, &cmd_mask)) {
> +		pr_debug("%s: Unsupported cmd=%u\n", __func__, cmd);
> +		return -EINVAL;
> +	} else if (cmd == ND_CMD_CALL) {
> +
> +		/* Verify the envelop package */
> +		if (!buf || buf_len < sizeof(struct nd_papr_scm_cmd_pkg)) {
> +			pr_debug("%s: Invalid pkg size=%u\n", __func__,
> +				 buf_len);
> +			return -EINVAL;
> +		}
> +
> +		/* Verify that the DSM command family is valid */
> +		if (pkg->hdr.nd_family != NVDIMM_FAMILY_PAPR_SCM) {
> +			pr_debug("%s: Invalid pkg family=0x%llx\n", __func__,
> +				 pkg->hdr.nd_family);
> +			return -EINVAL;
> +
> +		}
> +
> +		/* We except a payload with all DSM commands */
> +		if (papr_scm_pcmd_to_payload(pkg) == NULL) {
> +			pr_debug("%s: Empty payload for sub-command=0x%llx\n",
> +				 __func__, pkg->hdr.nd_command);
> +			return -EINVAL;
> +		}
> +	}
> +
> +	/* Command looks valid */
> +	return 0;
> +}
> +
> +static int papr_scm_service_dsm(struct papr_scm_priv *p,
> +				struct nd_papr_scm_cmd_pkg *call_pkg)
> +{
> +	/* unknown subcommands return error in packages */
> +	if (call_pkg->hdr.nd_command <= DSM_PAPR_SCM_MIN ||
> +	    call_pkg->hdr.nd_command >= DSM_PAPR_SCM_MAX) {
> +		pr_debug("Invalid DSM command 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:
> +		pr_debug("Unsupported DSM command 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_papr_scm_cmd_pkg *call_pkg = NULL;
> +	int rc;
>  
> -	/* Only dimm-specific calls are supported atm */
> -	if (!nvdimm)
> -		return -EINVAL;
> +	/* 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("%s: Invalid cmd=0x%x. Err=%d\n", __func__,
> +			 cmd, *cmd_rc);
> +		return *cmd_rc;
> +	}
>  
>  	p = nvdimm_provider_data(nvdimm);
>  
> @@ -313,13 +392,19 @@ 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_papr_cmd_pkg(buf);
> +		*cmd_rc = papr_scm_service_dsm(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)
> -- 
> 2.25.1
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