xref: /illumos-gate/usr/src/uts/sun4v/io/dr_cpu.c (revision 4e18e297380f99d39327599157792494d044942a)

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

/*
 * Copyright 2019 Joyent, Inc.
 */

/*
 * sun4v CPU DR Module
 */

#include <sys/modctl.h>
#include <sys/processor.h>
#include <sys/cpuvar.h>
#include <sys/cpupart.h>
#include <sys/sunddi.h>
#include <sys/sunndi.h>
#include <sys/note.h>
#include <sys/sysevent/dr.h>
#include <sys/hypervisor_api.h>
#include <sys/mach_descrip.h>
#include <sys/mdesc.h>
#include <sys/ds.h>
#include <sys/drctl.h>
#include <sys/dr_util.h>
#include <sys/dr_cpu.h>
#include <sys/promif.h>
#include <sys/machsystm.h>


static struct modlmisc modlmisc = {
	&mod_miscops,
	"sun4v CPU DR"
};

static struct modlinkage modlinkage = {
	MODREV_1,
	(void *)&modlmisc,
	NULL
};

typedef int (*fn_t)(processorid_t, int *, boolean_t);

/*
 * Global DS Handle
 */
static ds_svc_hdl_t ds_handle;

/*
 * Supported DS Capability Versions
 */
static ds_ver_t		dr_cpu_vers[] = { { 1, 1 }, { 1, 0 } };
#define	DR_CPU_NVERS	(sizeof (dr_cpu_vers) / sizeof (dr_cpu_vers[0]))

static ds_ver_t		version;

/*
 * DS Capability Description
 */
static ds_capability_t dr_cpu_cap = {
	DR_CPU_DS_ID,		/* svc_id */
	dr_cpu_vers,		/* vers */
	DR_CPU_NVERS		/* nvers */
};

#define	DRCPU_VERS_EQ(_maj, _min) \
	((version.major == (_maj)) && (version.minor == (_min)))

#define	DRCPU_VERS_GTEQ(_maj, _min) \
	((version.major > (_maj)) ||					\
	((version.major == (_maj)) && (version.minor >= (_min))))

/*
 * DS Callbacks
 */
static void dr_cpu_reg_handler(ds_cb_arg_t, ds_ver_t *, ds_svc_hdl_t);
static void dr_cpu_unreg_handler(ds_cb_arg_t arg);
static void dr_cpu_data_handler(ds_cb_arg_t arg, void *buf, size_t buflen);

/*
 * DS Client Ops Vector
 */
static ds_clnt_ops_t dr_cpu_ops = {
	dr_cpu_reg_handler,	/* ds_reg_cb */
	dr_cpu_unreg_handler,	/* ds_unreg_cb */
	dr_cpu_data_handler,	/* ds_data_cb */
	NULL			/* cb_arg */
};

/*
 * Operation Results
 *
 * Used internally to gather results while an operation on a
 * list of CPUs is in progress. In particular, it is used to
 * keep track of which CPUs have already failed so that they are
 * not processed further, and the manner in which they failed.
 */
typedef struct {
	uint32_t	cpuid;
	uint32_t	result;
	uint32_t	status;
	char		*string;
} dr_cpu_res_t;

#define	DR_CPU_MAX_ERR_LEN	64	/* maximum error string length */

/*
 * Internal Functions
 */
static int dr_cpu_init(void);
static int dr_cpu_fini(void);

static int dr_cpu_list_wrk(dr_cpu_hdr_t *, dr_cpu_hdr_t **, int *);
static int dr_cpu_list_status(dr_cpu_hdr_t *, dr_cpu_hdr_t **, int *);

static int dr_cpu_unconfigure(processorid_t, int *status, boolean_t force);
static int dr_cpu_configure(processorid_t, int *status, boolean_t force);
static int dr_cpu_status(processorid_t, int *status);

static void dr_cpu_check_cpus(dr_cpu_hdr_t *req, dr_cpu_res_t *res);
static void dr_cpu_check_psrset(uint32_t *cpuids, dr_cpu_res_t *res, int nres);
static int dr_cpu_check_bound_thr(cpu_t *cp, dr_cpu_res_t *res);

static dr_cpu_res_t *dr_cpu_res_array_init(dr_cpu_hdr_t *, drctl_rsrc_t *, int);
static void dr_cpu_res_array_fini(dr_cpu_res_t *res, int nres);
static size_t dr_cpu_pack_response(dr_cpu_hdr_t *req, dr_cpu_res_t *res,
    dr_cpu_hdr_t **respp);

static int dr_cpu_probe(processorid_t newcpuid);
static int dr_cpu_deprobe(processorid_t cpuid);

static dev_info_t *dr_cpu_find_node(processorid_t cpuid);
static mde_cookie_t dr_cpu_find_node_md(processorid_t, md_t *, mde_cookie_t *);

int
_init(void)
{
	int	status;

	/* check that CPU DR is enabled */
	if (dr_is_disabled(DR_TYPE_CPU)) {
		cmn_err(CE_CONT, "!CPU DR is disabled\n");
		return (-1);
	}

	if ((status = dr_cpu_init()) != 0) {
		cmn_err(CE_NOTE, "CPU DR initialization failed");
		return (status);
	}

	if ((status = mod_install(&modlinkage)) != 0) {
		(void) dr_cpu_fini();
	}

	return (status);
}

int
_info(struct modinfo *modinfop)
{
	return (mod_info(&modlinkage, modinfop));
}

int dr_cpu_allow_unload;

int
_fini(void)
{
	int	status;

	if (dr_cpu_allow_unload == 0)
		return (EBUSY);

	if ((status = mod_remove(&modlinkage)) == 0) {
		(void) dr_cpu_fini();
	}

	return (status);
}

static int
dr_cpu_init(void)
{
	int	rv;

	if ((rv = ds_cap_init(&dr_cpu_cap, &dr_cpu_ops)) != 0) {
		cmn_err(CE_NOTE, "ds_cap_init failed: %d", rv);
		return (-1);
	}

	return (0);
}

static int
dr_cpu_fini(void)
{
	int	rv;

	if ((rv = ds_cap_fini(&dr_cpu_cap)) != 0) {
		cmn_err(CE_NOTE, "ds_cap_fini failed: %d", rv);
		return (-1);
	}

	return (0);
}

static void
dr_cpu_reg_handler(ds_cb_arg_t arg, ds_ver_t *ver, ds_svc_hdl_t hdl)
{
	DR_DBG_CPU("reg_handler: arg=0x%p, ver=%d.%d, hdl=0x%lx\n", arg,
	    ver->major, ver->minor, hdl);

	version.major = ver->major;
	version.minor = ver->minor;
	ds_handle = hdl;
}

static void
dr_cpu_unreg_handler(ds_cb_arg_t arg)
{
	DR_DBG_CPU("unreg_handler: arg=0x%p\n", arg);

	ds_handle = DS_INVALID_HDL;
}

static void
dr_cpu_data_handler(ds_cb_arg_t arg, void *buf, size_t buflen)
{
	_NOTE(ARGUNUSED(arg))

	dr_cpu_hdr_t	*req = buf;
	dr_cpu_hdr_t	err_resp;
	dr_cpu_hdr_t	*resp = &err_resp;
	int		resp_len = 0;
	int		rv;

	/*
	 * Sanity check the message
	 */
	if (buflen < sizeof (dr_cpu_hdr_t)) {
		DR_DBG_CPU("incoming message short: expected at least %ld "
		    "bytes, received %ld\n", sizeof (dr_cpu_hdr_t), buflen);
		goto done;
	}

	if (req == NULL) {
		DR_DBG_CPU("empty message: expected at least %ld bytes\n",
		    sizeof (dr_cpu_hdr_t));
		goto done;
	}

	DR_DBG_CPU("incoming request:\n");
	DR_DBG_DUMP_MSG(buf, buflen);

	if (req->num_records > NCPU) {
		DR_DBG_CPU("CPU list too long: %d when %d is the maximum\n",
		    req->num_records, NCPU);
		goto done;
	}

	if (req->num_records == 0) {
		DR_DBG_CPU("No CPU specified for operation\n");
		goto done;
	}

	/*
	 * Process the command
	 */
	switch (req->msg_type) {
	case DR_CPU_CONFIGURE:
	case DR_CPU_UNCONFIGURE:
	case DR_CPU_FORCE_UNCONFIG:
		if ((rv = dr_cpu_list_wrk(req, &resp, &resp_len)) != 0) {
			DR_DBG_CPU("%s%s failed (%d)\n",
			    (req->msg_type == DR_CPU_CONFIGURE) ?
			    "CPU configure" : "CPU unconfigure",
			    (req->msg_type == DR_CPU_FORCE_UNCONFIG) ?
			    " (forced)" : "", rv);
		}
		break;

	case DR_CPU_STATUS:
		if ((rv = dr_cpu_list_status(req, &resp, &resp_len)) != 0)
			DR_DBG_CPU("CPU status failed (%d)\n", rv);
		break;

	default:
		cmn_err(CE_NOTE, "unsupported DR operation (%d)",
		    req->msg_type);
		break;
	}

done:
	/* check if an error occurred */
	if (resp == &err_resp) {
		resp->req_num = (req) ? req->req_num : 0;
		resp->msg_type = DR_CPU_ERROR;
		resp->num_records = 0;
		resp_len = sizeof (dr_cpu_hdr_t);
	}

	DR_DBG_CPU("outgoing response:\n");
	DR_DBG_DUMP_MSG(resp, resp_len);

	/* send back the response */
	if (ds_cap_send(ds_handle, resp, resp_len) != 0) {
		DR_DBG_CPU("ds_send failed\n");
	}

	/* free any allocated memory */
	if (DRCPU_VERS_GTEQ(1, 1) || (resp != &err_resp)) {
		DR_DBG_KMEM("%s: free addr %p size %d\n",
		    __func__, (void *)resp, resp_len);
		kmem_free(resp, resp_len);
	}
}

/*
 * Create a response message which consists of a header followed
 * by the error string passed in.
 */
static size_t
dr_cpu_err_resp(dr_cpu_hdr_t *req, dr_cpu_hdr_t **respp, char *msg)
{
	size_t size;
	dr_cpu_hdr_t *resp;

	ASSERT((msg != NULL) && (strlen(msg) > 0));

	size = sizeof (*req) + strlen(msg) + 1;
	resp = kmem_alloc(size, KM_SLEEP);
	DR_DBG_KMEM("%s: alloc addr %p size %ld\n",
	    __func__, (void *)resp, size);

	resp->req_num = req->req_num;
	resp->msg_type = DR_CPU_ERROR;
	resp->num_records = 0;

	(void) strcpy((char *)(resp) + sizeof (*resp), msg);

	*respp = resp;

	return (size);
}

/*
 * Common routine to config or unconfig multiple cpus.  The unconfig
 * case checks with the OS to see if the removal of cpus will be
 * permitted, but can be overridden by the "force" version of the
 * command.  Otherwise, the logic for both cases is identical.
 *
 * Note: Do not modify result buffer or length on error.
 */
static int
dr_cpu_list_wrk(dr_cpu_hdr_t *req, dr_cpu_hdr_t **resp, int *resp_len)
{
	int		rv;
	int		idx;
	int		count;
	fn_t		dr_fn;
	int		se_hint;
	boolean_t	force = B_FALSE;
	uint32_t	*req_cpus;
	dr_cpu_res_t	*res;
	int		drctl_cmd;
	int		drctl_flags = 0;
	drctl_rsrc_t	*drctl_req;
	size_t		drctl_req_len;
	drctl_resp_t	*drctl_resp;
	drctl_rsrc_t	*drctl_rsrc;
	size_t		drctl_resp_len = 0;
	drctl_cookie_t	drctl_res_ck;

	ASSERT((req != NULL) && (req->num_records != 0));

	count = req->num_records;

	/*
	 * Extract all information that is specific
	 * to the various types of operations.
	 */
	switch (req->msg_type) {
	case DR_CPU_CONFIGURE:
		dr_fn = dr_cpu_configure;
		drctl_cmd = DRCTL_CPU_CONFIG_REQUEST;
		se_hint = SE_HINT_INSERT;
		break;
	case DR_CPU_FORCE_UNCONFIG:
		drctl_flags = DRCTL_FLAG_FORCE;
		force = B_TRUE;
		/* FALLTHROUGH */
	case DR_CPU_UNCONFIGURE:
		dr_fn = dr_cpu_unconfigure;
		drctl_cmd = DRCTL_CPU_UNCONFIG_REQUEST;
		se_hint = SE_HINT_REMOVE;
		break;
	default:
		/* Programming error if we reach this. */
		cmn_err(CE_NOTE,
		    "%s: bad msg_type %d\n", __func__, req->msg_type);
		ASSERT(0);
		return (-1);
	}

	/* the incoming array of cpuids to operate on */
	req_cpus = DR_CPU_CMD_CPUIDS(req);

	/* allocate drctl request msg based on incoming resource count */
	drctl_req_len = sizeof (drctl_rsrc_t) * count;
	drctl_req = kmem_zalloc(drctl_req_len, KM_SLEEP);
	DR_DBG_KMEM("%s: alloc addr %p size %ld\n",
	    __func__, (void *)drctl_req, drctl_req_len);

	/* copy the cpuids for the drctl call from the incoming request msg */
	for (idx = 0; idx < count; idx++)
		drctl_req[idx].res_cpu_id = req_cpus[idx];

	rv = drctl_config_init(drctl_cmd, drctl_flags, drctl_req,
	    count, &drctl_resp, &drctl_resp_len, &drctl_res_ck);

	ASSERT((drctl_resp != NULL) && (drctl_resp_len != 0));

	if (rv != 0) {
		DR_DBG_CPU("%s: drctl_config_init "
		    "returned: %d\n", __func__, rv);

		if (DRCPU_VERS_EQ(1, 0)) {
			rv = -1;
		} else {
			ASSERT(DRCPU_VERS_GTEQ(1, 1));
			ASSERT(drctl_resp->resp_type == DRCTL_RESP_ERR);

			*resp_len = dr_cpu_err_resp(req,
			    resp, drctl_resp->resp_err_msg);
		}

		DR_DBG_KMEM("%s: free addr %p size %ld\n",
		    __func__, (void *)drctl_resp, drctl_resp_len);
		kmem_free(drctl_resp, drctl_resp_len);
		DR_DBG_KMEM("%s: free addr %p size %ld\n",
		    __func__, (void *)drctl_req, drctl_req_len);
		kmem_free(drctl_req, drctl_req_len);

		return (rv);
	}

	ASSERT(drctl_resp->resp_type == DRCTL_RESP_OK);

	drctl_rsrc = drctl_resp->resp_resources;

	/* create the result scratch array */
	res = dr_cpu_res_array_init(req, drctl_rsrc, count);

	/*
	 * For unconfigure, check if there are any conditions
	 * that will cause the operation to fail. These are
	 * performed before the actual unconfigure attempt so
	 * that a meaningful error message can be generated.
	 */
	if (req->msg_type != DR_CPU_CONFIGURE)
		dr_cpu_check_cpus(req, res);

	/* perform the specified operation on each of the CPUs */
	for (idx = 0; idx < count; idx++) {
		int result;
		int status;

		/*
		 * If no action will be taken against the current
		 * CPU, update the drctl resource information to
		 * ensure that it gets recovered properly during
		 * the drctl fini() call.
		 */
		if (res[idx].result != DR_CPU_RES_OK) {
			drctl_req[idx].status = DRCTL_STATUS_CONFIG_FAILURE;
			continue;
		}

		/* call the function to perform the actual operation */
		result = (*dr_fn)(req_cpus[idx], &status, force);

		/* save off results of the operation */
		res[idx].result = result;
		res[idx].status = status;

		/* save result for drctl fini() reusing init() msg memory */
		drctl_req[idx].status = (result != DR_CPU_RES_OK) ?
		    DRCTL_STATUS_CONFIG_FAILURE : DRCTL_STATUS_CONFIG_SUCCESS;

		DR_DBG_CPU("%s: cpuid %d status %d result %d off '%s'\n",
		    __func__, req_cpus[idx], drctl_req[idx].status, result,
		    (res[idx].string) ? res[idx].string : "");
	}

	if ((rv = drctl_config_fini(&drctl_res_ck, drctl_req, count)) != 0)
		DR_DBG_CPU("%s: drctl_config_fini "
		    "returned: %d\n", __func__, rv);

	/*
	 * Operation completed without any fatal errors.
	 * Pack the response for transmission.
	 */
	*resp_len = dr_cpu_pack_response(req, res, resp);

	/* notify interested parties about the operation */
	dr_generate_event(DR_TYPE_CPU, se_hint);

	/*
	 * Deallocate any scratch memory.
	 */
	DR_DBG_KMEM("%s: free addr %p size %ld\n",
	    __func__, (void *)drctl_resp, drctl_resp_len);
	kmem_free(drctl_resp, drctl_resp_len);
	DR_DBG_KMEM("%s: free addr %p size %ld\n",
	    __func__, (void *)drctl_req, drctl_req_len);
	kmem_free(drctl_req, drctl_req_len);

	dr_cpu_res_array_fini(res, count);

	return (0);
}

/*
 * Allocate and initialize a result array based on the initial
 * drctl operation. A valid result array is always returned.
 */
static dr_cpu_res_t *
dr_cpu_res_array_init(dr_cpu_hdr_t *req, drctl_rsrc_t *rsrc, int nrsrc)
{
	int		idx;
	dr_cpu_res_t	*res;
	char		*err_str;
	size_t		err_len;

	/* allocate zero filled buffer to initialize fields */
	res = kmem_zalloc(nrsrc * sizeof (dr_cpu_res_t), KM_SLEEP);
	DR_DBG_KMEM("%s: alloc addr %p size %ld\n",
	    __func__, (void *)res, nrsrc * sizeof (dr_cpu_res_t));

	/*
	 * Fill in the result information for each resource.
	 */
	for (idx = 0; idx < nrsrc; idx++) {
		res[idx].cpuid = rsrc[idx].res_cpu_id;
		res[idx].result = DR_CPU_RES_OK;

		if (rsrc[idx].status == DRCTL_STATUS_ALLOW)
			continue;

		/*
		 * Update the state information for this CPU.
		 */
		res[idx].result = DR_CPU_RES_BLOCKED;
		res[idx].status = (req->msg_type == DR_CPU_CONFIGURE) ?
		    DR_CPU_STAT_UNCONFIGURED : DR_CPU_STAT_CONFIGURED;

		/*
		 * If an error string exists, copy it out of the
		 * message buffer. This eliminates any dependency
		 * on the memory allocated for the message buffer
		 * itself.
		 */
		if (rsrc[idx].offset != 0) {
			err_str = (char *)rsrc + rsrc[idx].offset;
			err_len = strlen(err_str) + 1;

			res[idx].string = kmem_alloc(err_len, KM_SLEEP);
			DR_DBG_KMEM("%s: alloc addr %p size %ld\n",
			    __func__, (void *)(res[idx].string), err_len);
			bcopy(err_str, res[idx].string, err_len);
		}
	}

	return (res);
}

static void
dr_cpu_res_array_fini(dr_cpu_res_t *res, int nres)
{
	int	idx;
	size_t	str_len;

	for (idx = 0; idx < nres; idx++) {
		/* deallocate the error string if present */
		if (res[idx].string) {
			str_len = strlen(res[idx].string) + 1;
			DR_DBG_KMEM("%s: free addr %p size %ld\n",
			    __func__, (void *)(res[idx].string), str_len);
			kmem_free(res[idx].string, str_len);
		}
	}

	/* deallocate the result array itself */
	DR_DBG_KMEM("%s: free addr %p size %ld\n",
	    __func__, (void *)res, sizeof (dr_cpu_res_t) * nres);
	kmem_free(res, sizeof (dr_cpu_res_t) * nres);
}

/*
 * Allocate and pack a response message for transmission based
 * on the specified result array. A valid response message and
 * valid size information is always returned.
 */
static size_t
dr_cpu_pack_response(dr_cpu_hdr_t *req, dr_cpu_res_t *res, dr_cpu_hdr_t **respp)
{
	int		idx;
	dr_cpu_hdr_t	*resp;
	dr_cpu_stat_t	*resp_stat;
	size_t		resp_len;
	uint32_t	curr_off;
	caddr_t		curr_str;
	size_t		str_len;
	size_t		stat_len;
	int		nstat = req->num_records;

	/*
	 * Calculate the size of the response message
	 * and allocate an appropriately sized buffer.
	 */
	resp_len = 0;

	/* add the header size */
	resp_len += sizeof (dr_cpu_hdr_t);

	/* add the stat array size */
	stat_len = sizeof (dr_cpu_stat_t) * nstat;
	resp_len += stat_len;

	/* add the size of any error strings */
	for (idx = 0; idx < nstat; idx++) {
		if (res[idx].string != NULL) {
			resp_len += strlen(res[idx].string) + 1;
		}
	}

	/* allocate the message buffer */
	resp = kmem_zalloc(resp_len, KM_SLEEP);
	DR_DBG_KMEM("%s: alloc addr %p size %ld\n",
	    __func__, (void *)resp, resp_len);

	/*
	 * Fill in the header information.
	 */
	resp->req_num = req->req_num;
	resp->msg_type = DR_CPU_OK;
	resp->num_records = nstat;

	/*
	 * Fill in the stat information.
	 */
	resp_stat = DR_CPU_RESP_STATS(resp);

	/* string offsets start immediately after stat array */
	curr_off = sizeof (dr_cpu_hdr_t) + stat_len;
	curr_str = (char *)resp_stat + stat_len;

	for (idx = 0; idx < nstat; idx++) {
		resp_stat[idx].cpuid = res[idx].cpuid;
		resp_stat[idx].result = res[idx].result;
		resp_stat[idx].status = res[idx].status;

		if (res[idx].string != NULL) {
			/* copy over the error string */
			str_len = strlen(res[idx].string) + 1;
			bcopy(res[idx].string, curr_str, str_len);
			resp_stat[idx].string_off = curr_off;

			curr_off += str_len;
			curr_str += str_len;
		}
	}

	/* buffer should be exactly filled */
	ASSERT(curr_off == resp_len);

	*respp = resp;
	return (resp_len);
}

/*
 * Check for conditions that will prevent a CPU from being offlined.
 * This provides the opportunity to generate useful information to
 * help diagnose the failure rather than letting the offline attempt
 * fail in a more generic way.
 */
static void
dr_cpu_check_cpus(dr_cpu_hdr_t *req, dr_cpu_res_t *res)
{
	int		idx;
	cpu_t		*cp;
	uint32_t	*cpuids;

	ASSERT((req->msg_type == DR_CPU_UNCONFIGURE) ||
	    (req->msg_type == DR_CPU_FORCE_UNCONFIG));

	DR_DBG_CPU("dr_cpu_check_cpus...\n");

	/* array of cpuids start just after the header */
	cpuids = DR_CPU_CMD_CPUIDS(req);

	mutex_enter(&cpu_lock);

	/*
	 * Always check processor set membership first. The
	 * last CPU in a processor set will fail to offline
	 * even if the operation if forced, so any failures
	 * should always be reported.
	 */
	dr_cpu_check_psrset(cpuids, res, req->num_records);

	/* process each cpu that is part of the request */
	for (idx = 0; idx < req->num_records; idx++) {

		/* nothing to check if the CPU has already failed */
		if (res[idx].result != DR_CPU_RES_OK)
			continue;

		if ((cp = cpu_get(cpuids[idx])) == NULL)
			continue;

		/*
		 * Only check if there are bound threads if the
		 * operation is not a forced unconfigure. In a
		 * forced request, threads are automatically
		 * unbound before they are offlined.
		 */
		if (req->msg_type == DR_CPU_UNCONFIGURE) {
			/*
			 * The return value is only interesting if other
			 * checks are added to this loop and a decision
			 * is needed on whether to continue checking.
			 */
			(void) dr_cpu_check_bound_thr(cp, &res[idx]);
		}
	}

	mutex_exit(&cpu_lock);
}

/*
 * Examine the processor set configuration for the specified
 * CPUs and see if the unconfigure operation would result in
 * trying to remove the last CPU in any processor set.
 */
static void
dr_cpu_check_psrset(uint32_t *cpuids, dr_cpu_res_t *res, int nres)
{
	int		cpu_idx;
	int		set_idx;
	cpu_t		*cp;
	cpupart_t	*cpp;
	char		err_str[DR_CPU_MAX_ERR_LEN];
	size_t		err_len;
	struct {
		cpupart_t	*cpp;
		int		ncpus;
	} *psrset;

	ASSERT(MUTEX_HELD(&cpu_lock));

	/*
	 * Allocate a scratch array to count the CPUs in
	 * the various processor sets. A CPU always belongs
	 * to exactly one processor set, so by definition,
	 * the scratch array never needs to be larger than
	 * the number of CPUs.
	 */
	psrset = kmem_zalloc(sizeof (*psrset) * nres, KM_SLEEP);
	DR_DBG_KMEM("%s: alloc addr %p size %ld\n",
	    __func__, (void *)psrset, sizeof (*psrset) * nres);

	for (cpu_idx = 0; cpu_idx < nres; cpu_idx++) {

		/* skip any CPUs that have already failed */
		if (res[cpu_idx].result != DR_CPU_RES_OK)
			continue;

		if ((cp = cpu_get(cpuids[cpu_idx])) == NULL)
			continue;

		cpp = cp->cpu_part;

		/* lookup the set this CPU belongs to */
		for (set_idx = 0; set_idx < nres; set_idx++) {

			/* matching set found */
			if (cpp == psrset[set_idx].cpp)
				break;

			/* set not found, start a new entry */
			if (psrset[set_idx].cpp == NULL) {
				psrset[set_idx].cpp = cpp;
				psrset[set_idx].ncpus = cpp->cp_ncpus;
				break;
			}
		}

		ASSERT(set_idx != nres);

		/*
		 * Remove the current CPU from the set total but only
		 * generate an error for the last CPU. The correct CPU
		 * will get the error because the unconfigure attempts
		 * will occur in the same order in which the CPUs are
		 * examined in this loop.  The cp_ncpus field of a
		 * cpupart_t counts only online cpus, so it is safe
		 * to remove an offline cpu without testing ncpus.
		 */
		if (cpu_is_offline(cp))
			continue;

		if (--psrset[set_idx].ncpus == 0) {
			/*
			 * Fill in the various pieces of information
			 * to report that the operation will fail.
			 */
			res[cpu_idx].result = DR_CPU_RES_BLOCKED;
			res[cpu_idx].status = DR_CPU_STAT_CONFIGURED;

			(void) snprintf(err_str, DR_CPU_MAX_ERR_LEN,
			    "last online cpu in processor set %d", cpp->cp_id);

			err_len = strlen(err_str) + 1;

			res[cpu_idx].string = kmem_alloc(err_len, KM_SLEEP);
			DR_DBG_KMEM("%s: alloc addr %p size %ld\n",
			    __func__, (void *)(res[cpu_idx].string), err_len);
			bcopy(err_str, res[cpu_idx].string, err_len);

			DR_DBG_CPU("cpu %d: %s\n", cpuids[cpu_idx], err_str);
		}
	}

	DR_DBG_KMEM("%s: free addr %p size %ld\n",
	    __func__, (void *)psrset, sizeof (*psrset) * nres);
	kmem_free(psrset, sizeof (*psrset) * nres);
}

/*
 * Check if any threads are bound to the specified CPU. If the
 * condition is true, DR_CPU_RES_BLOCKED is returned and an error
 * string is generated and placed in the specified result structure.
 * Otherwise, DR_CPU_RES_OK is returned.
 */
static int
dr_cpu_check_bound_thr(cpu_t *cp, dr_cpu_res_t *res)
{
	int		nbound;
	proc_t		*pp;
	kthread_t	*tp;
	char		err_str[DR_CPU_MAX_ERR_LEN];
	size_t		err_len;

	/*
	 * Error string allocation makes an assumption
	 * that no blocking condition has been identified.
	 */
	ASSERT(res->result == DR_CPU_RES_OK);
	ASSERT(res->string == NULL);

	ASSERT(MUTEX_HELD(&cpu_lock));

	mutex_enter(&pidlock);

	nbound = 0;

	/*
	 * Walk the active processes, checking if each
	 * thread belonging to the process is bound.
	 */
	for (pp = practive; (pp != NULL) && (nbound <= 1); pp = pp->p_next) {
		mutex_enter(&pp->p_lock);

		tp = pp->p_tlist;

		if ((tp == NULL) || (pp->p_flag & SSYS)) {
			mutex_exit(&pp->p_lock);
			continue;
		}

		do {
			if (tp->t_bind_cpu != cp->cpu_id)
				continue;

			/*
			 * Update the running total of bound
			 * threads. Continue the search until
			 * it can be determined if more than
			 * one thread is bound to the CPU.
			 */
			if (++nbound > 1)
				break;

		} while ((tp = tp->t_forw) != pp->p_tlist);

		mutex_exit(&pp->p_lock);
	}

	mutex_exit(&pidlock);

	if (nbound) {
		/*
		 * Threads are bound to the CPU. Fill in
		 * various pieces of information to report
		 * that the operation will fail.
		 */
		res->result = DR_CPU_RES_BLOCKED;
		res->status = DR_CPU_STAT_CONFIGURED;

		(void) snprintf(err_str, DR_CPU_MAX_ERR_LEN, "cpu has bound "
		    "thread%s", (nbound > 1) ? "s" : "");

		err_len = strlen(err_str) + 1;

		res->string = kmem_alloc(err_len, KM_SLEEP);
		DR_DBG_KMEM("%s: alloc addr %p size %ld\n",
		    __func__, (void *)(res->string), err_len);
		bcopy(err_str, res->string, err_len);

		DR_DBG_CPU("cpu %d: %s\n", cp->cpu_id, err_str);
	}

	return (res->result);
}

/*
 * Do not modify result buffer or length on error.
 */
static int
dr_cpu_list_status(dr_cpu_hdr_t *req, dr_cpu_hdr_t **resp, int *resp_len)
{
	int		idx;
	int		result;
	int		status;
	int		rlen;
	uint32_t	*cpuids;
	dr_cpu_hdr_t	*rp;
	dr_cpu_stat_t	*stat;
	md_t		*mdp = NULL;
	int		num_nodes;
	int		listsz;
	mde_cookie_t	*listp = NULL;
	mde_cookie_t	cpunode;
	boolean_t	walk_md = B_FALSE;

	/* the incoming array of cpuids to configure */
	cpuids = DR_CPU_CMD_CPUIDS(req);

	/* allocate a response message */
	rlen = sizeof (dr_cpu_hdr_t);
	rlen += req->num_records * sizeof (dr_cpu_stat_t);
	rp = kmem_zalloc(rlen, KM_SLEEP);
	DR_DBG_KMEM("%s: alloc addr %p size %d\n", __func__, (void *)rp, rlen);

	/* fill in the known data */
	rp->req_num = req->req_num;
	rp->msg_type = DR_CPU_STATUS;
	rp->num_records = req->num_records;

	/* stat array for the response */
	stat = DR_CPU_RESP_STATS(rp);

	/* get the status for each of the CPUs */
	for (idx = 0; idx < req->num_records; idx++) {

		result = dr_cpu_status(cpuids[idx], &status);

		if (result == DR_CPU_RES_FAILURE)
			walk_md = B_TRUE;

		/* save off results of the status */
		stat[idx].cpuid = cpuids[idx];
		stat[idx].result = result;
		stat[idx].status = status;
	}

	if (walk_md == B_FALSE)
		goto done;

	/*
	 * At least one of the cpus did not have a CPU
	 * structure. So, consult the MD to determine if
	 * they are present.
	 */

	if ((mdp = md_get_handle()) == NULL) {
		DR_DBG_CPU("unable to initialize MD\n");
		goto done;
	}

	num_nodes = md_node_count(mdp);
	ASSERT(num_nodes > 0);

	listsz = num_nodes * sizeof (mde_cookie_t);
	listp = kmem_zalloc(listsz, KM_SLEEP);
	DR_DBG_KMEM("%s: alloc addr %p size %d\n",
	    __func__, (void *)listp, listsz);

	for (idx = 0; idx < req->num_records; idx++) {

		if (stat[idx].result != DR_CPU_RES_FAILURE)
			continue;

		/* check the MD for the current cpuid */
		cpunode = dr_cpu_find_node_md(stat[idx].cpuid, mdp, listp);

		stat[idx].result = DR_CPU_RES_OK;

		if (cpunode == MDE_INVAL_ELEM_COOKIE) {
			stat[idx].status = DR_CPU_STAT_NOT_PRESENT;
		} else {
			stat[idx].status = DR_CPU_STAT_UNCONFIGURED;
		}
	}

	DR_DBG_KMEM("%s: free addr %p size %d\n",
	    __func__, (void *)listp, listsz);
	kmem_free(listp, listsz);

	(void) md_fini_handle(mdp);

done:
	*resp = rp;
	*resp_len = rlen;

	return (0);
}

static int
dr_cpu_configure(processorid_t cpuid, int *status, boolean_t force)
{
	 _NOTE(ARGUNUSED(force))
	struct cpu	*cp;
	int		rv = 0;

	DR_DBG_CPU("dr_cpu_configure...\n");

	/*
	 * Build device tree node for the CPU
	 */
	if ((rv = dr_cpu_probe(cpuid)) != 0) {
		DR_DBG_CPU("failed to probe CPU %d (%d)\n", cpuid, rv);
		if (rv == EINVAL) {
			*status = DR_CPU_STAT_NOT_PRESENT;
			return (DR_CPU_RES_NOT_IN_MD);
		}
		*status = DR_CPU_STAT_UNCONFIGURED;
		return (DR_CPU_RES_FAILURE);
	}

	mutex_enter(&cpu_lock);

	/*
	 * Configure the CPU
	 */
	if ((cp = cpu_get(cpuid)) == NULL) {

		if ((rv = cpu_configure(cpuid)) != 0) {
			DR_DBG_CPU("failed to configure CPU %d (%d)\n",
			    cpuid, rv);
			rv = DR_CPU_RES_FAILURE;
			*status = DR_CPU_STAT_UNCONFIGURED;
			goto done;
		}

		DR_DBG_CPU("CPU %d configured\n", cpuid);

		/* CPU struct should exist now */
		cp = cpu_get(cpuid);
	}

	ASSERT(cp);

	/*
	 * Power on the CPU. In sun4v, this brings the stopped
	 * CPU into the guest from the Hypervisor.
	 */
	if (cpu_is_poweredoff(cp)) {

		if ((rv = cpu_poweron(cp)) != 0) {
			DR_DBG_CPU("failed to power on CPU %d (%d)\n",
			    cpuid, rv);
			rv = DR_CPU_RES_FAILURE;
			*status = DR_CPU_STAT_UNCONFIGURED;
			goto done;
		}

		DR_DBG_CPU("CPU %d powered on\n", cpuid);
	}

	/*
	 * Online the CPU
	 */
	if (cpu_is_offline(cp)) {

		if ((rv = cpu_online(cp, 0)) != 0) {
			DR_DBG_CPU("failed to online CPU %d (%d)\n",
			    cpuid, rv);
			rv = DR_CPU_RES_FAILURE;
			/* offline is still configured */
			*status = DR_CPU_STAT_CONFIGURED;
			goto done;
		}

		DR_DBG_CPU("CPU %d online\n", cpuid);
	}

	rv = DR_CPU_RES_OK;
	*status = DR_CPU_STAT_CONFIGURED;

done:
	mutex_exit(&cpu_lock);

	return (rv);
}

static int
dr_cpu_unconfigure(processorid_t cpuid, int *status, boolean_t force)
{
	struct cpu	*cp;
	int		rv = 0;
	int		cpu_flags;

	DR_DBG_CPU("dr_cpu_unconfigure%s...\n", (force) ? " (force)" : "");

	mutex_enter(&cpu_lock);

	cp = cpu_get(cpuid);

	if (cp == NULL) {
		/*
		 * As OS CPU structures are already torn down proceed
		 * to deprobe device tree to make sure the device tree
		 * is up do date.
		 */
		goto deprobe;
	}

	ASSERT(cp->cpu_id == cpuid);

	/*
	 * Offline the CPU
	 */
	if (cpu_is_active(cp)) {

		/* set the force flag correctly */
		cpu_flags = (force) ? CPU_FORCED : 0;

		/*
		 * Before we take the CPU offline, we first enable interrupts.
		 * Otherwise, cpu_offline() might reject the request.  Note:
		 * if the offline subsequently fails, the target cpu will be
		 * left with interrupts enabled.  This is consistent with the
		 * behavior of psradm(8) and p_online(2).
		 */
		cpu_intr_enable(cp);

		if ((rv = cpu_offline(cp, cpu_flags)) != 0) {
			DR_DBG_CPU("failed to offline CPU %d (%d)\n",
			    cpuid, rv);

			rv = DR_CPU_RES_FAILURE;
			*status = DR_CPU_STAT_CONFIGURED;
			mutex_exit(&cpu_lock);
			return (rv);
		}

		DR_DBG_CPU("CPU %d offline\n", cpuid);
	}

	/*
	 * Power off the CPU. In sun4v, this puts the running
	 * CPU into the stopped state in the Hypervisor.
	 */
	if (!cpu_is_poweredoff(cp)) {

		if ((rv = cpu_poweroff(cp)) != 0) {
			DR_DBG_CPU("failed to power off CPU %d (%d)\n",
			    cpuid, rv);
			rv = DR_CPU_RES_FAILURE;
			*status = DR_CPU_STAT_CONFIGURED;
			mutex_exit(&cpu_lock);
			return (rv);
		}

		DR_DBG_CPU("CPU %d powered off\n", cpuid);
	}

	/*
	 * Unconfigure the CPU
	 */
	if ((rv = cpu_unconfigure(cpuid)) != 0) {
		DR_DBG_CPU("failed to unconfigure CPU %d (%d)\n", cpuid, rv);
		rv = DR_CPU_RES_FAILURE;
		*status = DR_CPU_STAT_UNCONFIGURED;
		mutex_exit(&cpu_lock);
		return (rv);
	}

	DR_DBG_CPU("CPU %d unconfigured\n", cpuid);

deprobe:
	mutex_exit(&cpu_lock);
	/*
	 * Tear down device tree.
	 */
	if ((rv = dr_cpu_deprobe(cpuid)) != 0) {
		DR_DBG_CPU("failed to deprobe CPU %d (%d)\n", cpuid, rv);
		rv = DR_CPU_RES_FAILURE;
		*status = DR_CPU_STAT_UNCONFIGURED;
		return (rv);
	}

	rv = DR_CPU_RES_OK;
	*status = DR_CPU_STAT_UNCONFIGURED;

	return (rv);
}

/*
 * Determine the state of a CPU. If the CPU structure is not present,
 * it does not attempt to determine whether or not the CPU is in the
 * MD. It is more efficient to do this at the higher level for all
 * CPUs since it may not even be necessary to search the MD if all
 * the CPUs are accounted for. Returns DR_CPU_RES_OK if the CPU
 * structure is present, and DR_CPU_RES_FAILURE otherwise as a signal
 * that an MD walk is necessary.
 */
static int
dr_cpu_status(processorid_t cpuid, int *status)
{
	int		rv;
	struct cpu	*cp;

	DR_DBG_CPU("dr_cpu_status...\n");

	mutex_enter(&cpu_lock);

	if ((cp = cpu_get(cpuid)) == NULL) {
		/* need to check if cpu is in the MD */
		rv = DR_CPU_RES_FAILURE;
		goto done;
	}

	if (cpu_is_poweredoff(cp)) {
		/*
		 * The CPU is powered off, so it is considered
		 * unconfigured from the service entity point of
		 * view. The CPU is not available to the system
		 * and intervention by the service entity would
		 * be required to change that.
		 */
		*status = DR_CPU_STAT_UNCONFIGURED;
	} else {
		/*
		 * The CPU is powered on, so it is considered
		 * configured from the service entity point of
		 * view. It is available for use by the system
		 * and service entities are not concerned about
		 * the operational status (offline, online, etc.)
		 * of the CPU in terms of DR.
		 */
		*status = DR_CPU_STAT_CONFIGURED;
	}

	rv = DR_CPU_RES_OK;

done:
	mutex_exit(&cpu_lock);

	return (rv);
}

typedef struct {
	md_t		*mdp;
	mde_cookie_t	cpunode;
	dev_info_t	*dip;
} cb_arg_t;

#define	STR_ARR_LEN	5

static int
new_cpu_node(dev_info_t *new_node, void *arg, uint_t flags)
{
	_NOTE(ARGUNUSED(flags))

	char		*compat;
	uint64_t	freq;
	uint64_t	cpuid = 0;
	int		regbuf[4];
	int		len = 0;
	cb_arg_t	*cba;
	char		*str_arr[STR_ARR_LEN];
	char		*curr;
	int		idx = 0;

	DR_DBG_CPU("new_cpu_node...\n");

	cba = (cb_arg_t *)arg;

	/*
	 * Add 'name' property
	 */
	if (ndi_prop_update_string(DDI_DEV_T_NONE, new_node,
	    "name", "cpu") != DDI_SUCCESS) {
		DR_DBG_CPU("new_cpu_node: failed to create 'name' property\n");
		return (DDI_WALK_ERROR);
	}

	/*
	 * Add 'compatible' property
	 */
	if (md_get_prop_data(cba->mdp, cba->cpunode, "compatible",
	    (uint8_t **)(&compat), &len)) {
		DR_DBG_CPU("new_cpu_node: failed to read 'compatible' property "
		    "from MD\n");
		return (DDI_WALK_ERROR);
	}

	DR_DBG_CPU("'compatible' len is %d\n", len);

	/* parse the MD string array */
	curr = compat;
	while (curr < (compat + len)) {

		DR_DBG_CPU("adding '%s' to 'compatible' property\n", curr);

		str_arr[idx++] = curr;
		curr += strlen(curr) + 1;

		if (idx == STR_ARR_LEN) {
			DR_DBG_CPU("exceeded str_arr len (%d)\n", STR_ARR_LEN);
			break;
		}
	}

	if (ndi_prop_update_string_array(DDI_DEV_T_NONE, new_node,
	    "compatible", str_arr, idx) != DDI_SUCCESS) {
		DR_DBG_CPU("new_cpu_node: failed to create 'compatible' "
		    "property\n");
		return (DDI_WALK_ERROR);
	}

	/*
	 * Add 'device_type' property
	 */
	if (ndi_prop_update_string(DDI_DEV_T_NONE, new_node,
	    "device_type", "cpu") != DDI_SUCCESS) {
		DR_DBG_CPU("new_cpu_node: failed to create 'device_type' "
		    "property\n");
		return (DDI_WALK_ERROR);
	}

	/*
	 * Add 'clock-frequency' property
	 */
	if (md_get_prop_val(cba->mdp, cba->cpunode, "clock-frequency", &freq)) {
		DR_DBG_CPU("new_cpu_node: failed to read 'clock-frequency' "
		    "property from MD\n");
		return (DDI_WALK_ERROR);
	}

	if (ndi_prop_update_int(DDI_DEV_T_NONE, new_node,
	    "clock-frequency", freq) != DDI_SUCCESS) {
		DR_DBG_CPU("new_cpu_node: failed to create 'clock-frequency' "
		    "property\n");
		return (DDI_WALK_ERROR);
	}

	/*
	 * Add 'reg' (cpuid) property
	 */
	if (md_get_prop_val(cba->mdp, cba->cpunode, "id", &cpuid)) {
		DR_DBG_CPU("new_cpu_node: failed to read 'id' property "
		    "from MD\n");
		return (DDI_WALK_ERROR);
	}

	DR_DBG_CPU("new cpuid=0x%lx\n", cpuid);

	bzero(regbuf, 4 * sizeof (int));
	regbuf[0] = 0xc0000000 | cpuid;

	if (ndi_prop_update_int_array(DDI_DEV_T_NONE, new_node,
	    "reg", regbuf, 4) != DDI_SUCCESS) {
		DR_DBG_CPU("new_cpu_node: failed to create 'reg' property\n");
		return (DDI_WALK_ERROR);
	}

	cba->dip = new_node;

	return (DDI_WALK_TERMINATE);
}

static int
dr_cpu_probe(processorid_t cpuid)
{
	dev_info_t	*pdip;
	dev_info_t	*dip;
	devi_branch_t	br;
	md_t		*mdp = NULL;
	int		num_nodes;
	int		rv = 0;
	int		listsz;
	mde_cookie_t	*listp = NULL;
	cb_arg_t	cba;
	mde_cookie_t	cpunode;

	if ((dip = dr_cpu_find_node(cpuid)) != NULL) {
		/* nothing to do */
		e_ddi_branch_rele(dip);
		return (0);
	}

	if ((mdp = md_get_handle()) == NULL) {
		DR_DBG_CPU("unable to initialize machine description\n");
		return (-1);
	}

	num_nodes = md_node_count(mdp);
	ASSERT(num_nodes > 0);

	listsz = num_nodes * sizeof (mde_cookie_t);
	listp = kmem_zalloc(listsz, KM_SLEEP);
	DR_DBG_KMEM("%s: alloc addr %p size %d\n",
	    __func__, (void *)listp, listsz);

	cpunode = dr_cpu_find_node_md(cpuid, mdp, listp);

	if (cpunode == MDE_INVAL_ELEM_COOKIE) {
		rv = EINVAL;
		goto done;
	}

	/* pass in MD cookie for CPU */
	cba.mdp = mdp;
	cba.cpunode = cpunode;

	br.arg = (void *)&cba;
	br.type = DEVI_BRANCH_SID;
	br.create.sid_branch_create = new_cpu_node;
	br.devi_branch_callback = NULL;
	pdip = ddi_root_node();

	if ((rv = e_ddi_branch_create(pdip, &br, NULL, 0))) {
		DR_DBG_CPU("e_ddi_branch_create failed: %d\n", rv);
		rv = -1;
		goto done;
	}

	DR_DBG_CPU("CPU %d probed\n", cpuid);

	rv = 0;

done:
	if (listp) {
		DR_DBG_KMEM("%s: free addr %p size %d\n",
		    __func__, (void *)listp, listsz);
		kmem_free(listp, listsz);
	}

	if (mdp)
		(void) md_fini_handle(mdp);

	return (rv);
}

static int
dr_cpu_deprobe(processorid_t cpuid)
{
	dev_info_t	*fdip = NULL;
	dev_info_t	*dip;

	if ((dip = dr_cpu_find_node(cpuid)) == NULL) {
		DR_DBG_CPU("cpuid %d already deprobed\n", cpuid);
		return (0);
	}

	ASSERT(e_ddi_branch_held(dip));

	if (e_ddi_branch_destroy(dip, &fdip, 0)) {
		char *path = kmem_alloc(MAXPATHLEN, KM_SLEEP);

		DR_DBG_KMEM("%s: alloc addr %p size %d\n",
		    __func__, (void *)path, MAXPATHLEN);
		/*
		 * If non-NULL, fdip is held and must be released.
		 */
		if (fdip != NULL) {
			(void) ddi_pathname(fdip, path);
			ddi_release_devi(fdip);
		} else {
			(void) ddi_pathname(dip, path);
		}
		cmn_err(CE_NOTE, "node removal failed: %s (%p)",
		    path, (fdip) ? (void *)fdip : (void *)dip);

		DR_DBG_KMEM("%s: free addr %p size %d\n",
		    __func__, (void *)path, MAXPATHLEN);
		kmem_free(path, MAXPATHLEN);

		return (-1);
	}

	DR_DBG_CPU("CPU %d deprobed\n", cpuid);

	return (0);
}

typedef struct {
	processorid_t	cpuid;
	dev_info_t	*dip;
} dr_search_arg_t;

static int
dr_cpu_check_node(dev_info_t *dip, void *arg)
{
	char		*name;
	processorid_t	cpuid;
	dr_search_arg_t	*sarg = (dr_search_arg_t *)arg;

	if (dip == ddi_root_node()) {
		return (DDI_WALK_CONTINUE);
	}

	name = ddi_node_name(dip);

	if (strcmp(name, "cpu") != 0) {
		return (DDI_WALK_PRUNECHILD);
	}

	cpuid = ddi_prop_get_int(DDI_DEV_T_ANY, dip, DDI_PROP_DONTPASS,
	    "reg", -1);

	cpuid = PROM_CFGHDL_TO_CPUID(cpuid);

	DR_DBG_CPU("found cpuid=0x%x, looking for 0x%x\n", cpuid, sarg->cpuid);

	if (cpuid == sarg->cpuid) {
		DR_DBG_CPU("matching node\n");

		/* matching node must be returned held */
		if (!e_ddi_branch_held(dip))
			e_ddi_branch_hold(dip);

		sarg->dip = dip;
		return (DDI_WALK_TERMINATE);
	}

	return (DDI_WALK_CONTINUE);
}

/*
 * Walk the device tree to find the dip corresponding to the cpuid
 * passed in. If present, the dip is returned held. The caller must
 * release the hold on the dip once it is no longer required. If no
 * matching node if found, NULL is returned.
 */
static dev_info_t *
dr_cpu_find_node(processorid_t cpuid)
{
	dr_search_arg_t	arg;

	DR_DBG_CPU("dr_cpu_find_node...\n");

	arg.cpuid = cpuid;
	arg.dip = NULL;

	ddi_walk_devs(ddi_root_node(), dr_cpu_check_node, &arg);

	ASSERT((arg.dip == NULL) || (e_ddi_branch_held(arg.dip)));

	return ((arg.dip) ? arg.dip : NULL);
}

/*
 * Look up a particular cpuid in the MD. Returns the mde_cookie_t
 * representing that CPU if present, and MDE_INVAL_ELEM_COOKIE
 * otherwise. It is assumed the scratch array has already been
 * allocated so that it can accommodate the worst case scenario,
 * every node in the MD.
 */
static mde_cookie_t
dr_cpu_find_node_md(processorid_t cpuid, md_t *mdp, mde_cookie_t *listp)
{
	int		idx;
	int		nnodes;
	mde_cookie_t	rootnode;
	uint64_t	cpuid_prop;
	mde_cookie_t	result = MDE_INVAL_ELEM_COOKIE;

	rootnode = md_root_node(mdp);
	ASSERT(rootnode != MDE_INVAL_ELEM_COOKIE);

	/*
	 * Scan the DAG for all the CPU nodes
	 */
	nnodes = md_scan_dag(mdp, rootnode, md_find_name(mdp, "cpu"),
	    md_find_name(mdp, "fwd"), listp);

	if (nnodes < 0) {
		DR_DBG_CPU("Scan for CPUs failed\n");
		return (result);
	}

	DR_DBG_CPU("dr_cpu_find_node_md: found %d CPUs in the MD\n", nnodes);

	/*
	 * Find the CPU of interest
	 */
	for (idx = 0; idx < nnodes; idx++) {

		if (md_get_prop_val(mdp, listp[idx], "id", &cpuid_prop)) {
			DR_DBG_CPU("Missing 'id' property for CPU node %d\n",
			    idx);
			break;
		}

		if (cpuid_prop == cpuid) {
			/* found a match */
			DR_DBG_CPU("dr_cpu_find_node_md: found CPU %d "
			    "in MD\n", cpuid);
			result = listp[idx];
			break;
		}
	}

	if (result == MDE_INVAL_ELEM_COOKIE) {
		DR_DBG_CPU("CPU %d not in MD\n", cpuid);
	}

	return (result);
}