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

[Vaibhav Jain <vaibhav@linux.ibm.com>]

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.

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