/*
 * 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 (c) 2010, Intel Corporation.
 * All rights reserved.
 * Copyright 2018 Joyent, Inc.
 */

#include <sys/types.h>
#include <sys/param.h>
#include <sys/t_lock.h>
#include <sys/thread.h>
#include <sys/cpuvar.h>
#include <sys/x_call.h>
#include <sys/xc_levels.h>
#include <sys/cpu.h>
#include <sys/psw.h>
#include <sys/sunddi.h>
#include <sys/debug.h>
#include <sys/systm.h>
#include <sys/archsystm.h>
#include <sys/machsystm.h>
#include <sys/mutex_impl.h>
#include <sys/stack.h>
#include <sys/promif.h>
#include <sys/x86_archext.h>

/*
 * Implementation for cross-processor calls via interprocessor interrupts
 *
 * This implementation uses a message passing architecture to allow multiple
 * concurrent cross calls to be in flight at any given time. We use the cmpxchg
 * instruction, aka atomic_cas_ptr(), to implement simple efficient work
 * queues for message passing between CPUs with almost no need for regular
 * locking.  See xc_extract() and xc_insert() below.
 *
 * The general idea is that initiating a cross call means putting a message
 * on a target(s) CPU's work queue. Any synchronization is handled by passing
 * the message back and forth between initiator and target(s).
 *
 * Every CPU has xc_work_cnt, which indicates it has messages to process.
 * This value is incremented as message traffic is initiated and decremented
 * with every message that finishes all processing.
 *
 * The code needs no mfence or other membar_*() calls. The uses of
 * atomic_cas_ptr(), atomic_cas_32() and atomic_dec_32() for the message
 * passing are implemented with LOCK prefix instructions which are
 * equivalent to mfence.
 *
 * One interesting aspect of this implmentation is that it allows 2 or more
 * CPUs to initiate cross calls to intersecting sets of CPUs at the same time.
 * The cross call processing by the CPUs will happen in any order with only
 * a guarantee, for xc_call() and xc_sync(), that an initiator won't return
 * from cross calls before all slaves have invoked the function.
 *
 * The reason for this asynchronous approach is to allow for fast global
 * TLB shootdowns. If all CPUs, say N, tried to do a global TLB invalidation
 * on a different Virtual Address at the same time. The old code required
 * N squared IPIs. With this method, depending on timing, it could happen
 * with just N IPIs.
 *
 * Here are the normal transitions for XC_MSG_* values in ->xc_command. A
 * transition of "->" happens in the slave cpu and "=>" happens in the master
 * cpu as the messages are passed back and forth.
 *
 * FREE => ASYNC ->                       DONE => FREE
 * FREE => CALL ->                        DONE => FREE
 * FREE => SYNC -> WAITING => RELEASED -> DONE => FREE
 *
 * The interesting one above is ASYNC. You might ask, why not go directly
 * to FREE, instead of DONE? If it did that, it might be possible to exhaust
 * the master's xc_free list if a master can generate ASYNC messages faster
 * then the slave can process them. That could be handled with more complicated
 * handling. However since nothing important uses ASYNC, I've not bothered.
 */

/*
 * The default is to not enable collecting counts of IPI information, since
 * the updating of shared cachelines could cause excess bus traffic.
 */
uint_t xc_collect_enable = 0;
uint64_t xc_total_cnt = 0;      /* total #IPIs sent for cross calls */
uint64_t xc_multi_cnt = 0;      /* # times we piggy backed on another IPI */

/*
 * We allow for one high priority message at a time to happen in the system.
 * This is used for panic, kmdb, etc., so no locking is done.
 */
static volatile cpuset_t xc_priority_set_store;
static volatile ulong_t *xc_priority_set = CPUSET2BV(xc_priority_set_store);
static xc_data_t xc_priority_data;

/*
 * Decrement a CPU's work count
 */
static void
xc_decrement(struct machcpu *mcpu)
{
        atomic_dec_32(&mcpu->xc_work_cnt);
}

/*
 * Increment a CPU's work count and return the old value
 */
static int
xc_increment(struct machcpu *mcpu)
{
        int old;
        do {
                old = mcpu->xc_work_cnt;
        } while (atomic_cas_32(&mcpu->xc_work_cnt, old, old + 1) != old);
        return (old);
}

/*
 * Put a message into a queue. The insertion is atomic no matter
 * how many different inserts/extracts to the same queue happen.
 */
static void
xc_insert(void *queue, xc_msg_t *msg)
{
        xc_msg_t *old_head;

        /*
         * FREE messages should only ever be getting inserted into
         * the xc_master CPUs xc_free queue.
         */
        ASSERT(msg->xc_command != XC_MSG_FREE ||
            cpu[msg->xc_master] == NULL || /* possible only during init */
            queue == &cpu[msg->xc_master]->cpu_m.xc_free);

        do {
                old_head = (xc_msg_t *)*(volatile xc_msg_t **)queue;
                msg->xc_next = old_head;
        } while (atomic_cas_ptr(queue, old_head, msg) != old_head);
}

/*
 * Extract a message from a queue. The extraction is atomic only
 * when just one thread does extractions from the queue.
 * If the queue is empty, NULL is returned.
 */
static xc_msg_t *
xc_extract(xc_msg_t **queue)
{
        xc_msg_t *old_head;

        do {
                old_head = (xc_msg_t *)*(volatile xc_msg_t **)queue;
                if (old_head == NULL)
                        return (old_head);
        } while (atomic_cas_ptr(queue, old_head, old_head->xc_next) !=
            old_head);
        old_head->xc_next = NULL;
        return (old_head);
}

/*
 * Extract the next message from the CPU's queue, and place the message in
 * .xc_curmsg.  The latter is solely to make debugging (and ::xcall) more
 * useful.
 */
static xc_msg_t *
xc_get(void)
{
        struct machcpu *mcpup = &CPU->cpu_m;
        xc_msg_t *msg = xc_extract(&mcpup->xc_msgbox);
        mcpup->xc_curmsg = msg;
        return (msg);
}

/*
 * Initialize the machcpu fields used for cross calls
 */
static uint_t xc_initialized = 0;

void
xc_init_cpu(struct cpu *cpup)
{
        xc_msg_t *msg;
        int c;

        /*
         * Allocate message buffers for the new CPU.
         */
        for (c = 0; c < max_ncpus; ++c) {
                if (plat_dr_support_cpu()) {
                        /*
                         * Allocate a message buffer for every CPU possible
                         * in system, including our own, and add them to our xc
                         * message queue.
                         */
                        msg = kmem_zalloc(sizeof (*msg), KM_SLEEP);
                        msg->xc_command = XC_MSG_FREE;
                        msg->xc_master = cpup->cpu_id;
                        xc_insert(&cpup->cpu_m.xc_free, msg);
                } else if (cpu[c] != NULL && cpu[c] != cpup) {
                        /*
                         * Add a new message buffer to each existing CPU's free
                         * list, as well as one for my list for each of them.
                         * Note: cpu0 is statically inserted into cpu[] array,
                         * so need to check cpu[c] isn't cpup itself to avoid
                         * allocating extra message buffers for cpu0.
                         */
                        msg = kmem_zalloc(sizeof (*msg), KM_SLEEP);
                        msg->xc_command = XC_MSG_FREE;
                        msg->xc_master = c;
                        xc_insert(&cpu[c]->cpu_m.xc_free, msg);

                        msg = kmem_zalloc(sizeof (*msg), KM_SLEEP);
                        msg->xc_command = XC_MSG_FREE;
                        msg->xc_master = cpup->cpu_id;
                        xc_insert(&cpup->cpu_m.xc_free, msg);
                }
        }

        if (!plat_dr_support_cpu()) {
                /*
                 * Add one for self messages if CPU hotplug is disabled.
                 */
                msg = kmem_zalloc(sizeof (*msg), KM_SLEEP);
                msg->xc_command = XC_MSG_FREE;
                msg->xc_master = cpup->cpu_id;
                xc_insert(&cpup->cpu_m.xc_free, msg);
        }

        if (!xc_initialized)
                xc_initialized = 1;
}

void
xc_fini_cpu(struct cpu *cpup)
{
        xc_msg_t *msg;

        ASSERT((cpup->cpu_flags & CPU_READY) == 0);
        ASSERT(cpup->cpu_m.xc_msgbox == NULL);
        ASSERT(cpup->cpu_m.xc_work_cnt == 0);

        while ((msg = xc_extract(&cpup->cpu_m.xc_free)) != NULL) {
                kmem_free(msg, sizeof (*msg));
        }
}

#define XC_FLUSH_MAX_WAITS              1000

/* Flush inflight message buffers. */
int
xc_flush_cpu(struct cpu *cpup)
{
        int i;

        ASSERT((cpup->cpu_flags & CPU_READY) == 0);

        /*
         * Pause all working CPUs, which ensures that there's no CPU in
         * function xc_common().
         * This is used to work around a race condition window in xc_common()
         * between checking CPU_READY flag and increasing working item count.
         */
        pause_cpus(cpup, NULL);
        start_cpus();

        for (i = 0; i < XC_FLUSH_MAX_WAITS; i++) {
                if (cpup->cpu_m.xc_work_cnt == 0) {
                        break;
                }
                DELAY(1);
        }
        for (; i < XC_FLUSH_MAX_WAITS; i++) {
                if (!BT_TEST(xc_priority_set, cpup->cpu_id)) {
                        break;
                }
                DELAY(1);
        }

        return (i >= XC_FLUSH_MAX_WAITS ? ETIME : 0);
}

/*
 * X-call message processing routine. Note that this is used by both
 * senders and recipients of messages.
 *
 * We're protected against changing CPUs by either being in a high-priority
 * interrupt, having preemption disabled or by having a raised SPL.
 */
/*ARGSUSED*/
uint_t
xc_serv(caddr_t arg1, caddr_t arg2)
{
        struct machcpu *mcpup = &(CPU->cpu_m);
        xc_msg_t *msg;
        xc_data_t *data;
        xc_msg_t *xc_waiters = NULL;
        uint32_t num_waiting = 0;
        xc_func_t func;
        xc_arg_t a1;
        xc_arg_t a2;
        xc_arg_t a3;
        uint_t rc = DDI_INTR_UNCLAIMED;

        while (mcpup->xc_work_cnt != 0) {
                rc = DDI_INTR_CLAIMED;

                /*
                 * We may have to wait for a message to arrive.
                 */
                for (msg = NULL; msg == NULL; msg = xc_get()) {

                        /*
                         * Alway check for and handle a priority message.
                         */
                        if (BT_TEST(xc_priority_set, CPU->cpu_id)) {
                                func = xc_priority_data.xc_func;
                                a1 = xc_priority_data.xc_a1;
                                a2 = xc_priority_data.xc_a2;
                                a3 = xc_priority_data.xc_a3;
                                BT_ATOMIC_CLEAR(xc_priority_set, CPU->cpu_id);
                                xc_decrement(mcpup);
                                func(a1, a2, a3);
                                if (mcpup->xc_work_cnt == 0)
                                        return (rc);
                        }

                        /*
                         * wait for a message to arrive
                         */
                        SMT_PAUSE();
                }


                /*
                 * process the message
                 */
                switch (msg->xc_command) {

                /*
                 * ASYNC gives back the message immediately, then we do the
                 * function and return with no more waiting.
                 */
                case XC_MSG_ASYNC:
                        data = &cpu[msg->xc_master]->cpu_m.xc_data;
                        func = data->xc_func;
                        a1 = data->xc_a1;
                        a2 = data->xc_a2;
                        a3 = data->xc_a3;
                        msg->xc_command = XC_MSG_DONE;
                        xc_insert(&cpu[msg->xc_master]->cpu_m.xc_msgbox, msg);
                        if (func != NULL)
                                (void) (*func)(a1, a2, a3);
                        xc_decrement(mcpup);
                        break;

                /*
                 * SYNC messages do the call, then send it back to the master
                 * in WAITING mode
                 */
                case XC_MSG_SYNC:
                        data = &cpu[msg->xc_master]->cpu_m.xc_data;
                        if (data->xc_func != NULL)
                                (void) (*data->xc_func)(data->xc_a1,
                                    data->xc_a2, data->xc_a3);
                        msg->xc_command = XC_MSG_WAITING;
                        xc_insert(&cpu[msg->xc_master]->cpu_m.xc_msgbox, msg);
                        break;

                /*
                 * WAITING messsages are collected by the master until all
                 * have arrived. Once all arrive, we release them back to
                 * the slaves
                 */
                case XC_MSG_WAITING:
                        xc_insert(&xc_waiters, msg);
                        if (++num_waiting < mcpup->xc_wait_cnt)
                                break;
                        while ((msg = xc_extract(&xc_waiters)) != NULL) {
                                msg->xc_command = XC_MSG_RELEASED;
                                xc_insert(&cpu[msg->xc_slave]->cpu_m.xc_msgbox,
                                    msg);
                                --num_waiting;
                        }
                        if (num_waiting != 0)
                                panic("wrong number waiting");
                        mcpup->xc_wait_cnt = 0;
                        break;

                /*
                 * CALL messages do the function and then, like RELEASE,
                 * send the message is back to master as DONE.
                 */
                case XC_MSG_CALL:
                        data = &cpu[msg->xc_master]->cpu_m.xc_data;
                        if (data->xc_func != NULL)
                                (void) (*data->xc_func)(data->xc_a1,
                                    data->xc_a2, data->xc_a3);
                        /*FALLTHROUGH*/
                case XC_MSG_RELEASED:
                        msg->xc_command = XC_MSG_DONE;
                        xc_insert(&cpu[msg->xc_master]->cpu_m.xc_msgbox, msg);
                        xc_decrement(mcpup);
                        break;

                /*
                 * DONE means a slave has completely finished up.
                 * Once we collect all the DONE messages, we'll exit
                 * processing too.
                 */
                case XC_MSG_DONE:
                        msg->xc_command = XC_MSG_FREE;
                        xc_insert(&mcpup->xc_free, msg);
                        xc_decrement(mcpup);
                        break;

                case XC_MSG_FREE:
                        panic("free message 0x%p in msgbox", (void *)msg);
                        break;

                default:
                        panic("bad message 0x%p in msgbox", (void *)msg);
                        break;
                }

                CPU->cpu_m.xc_curmsg = NULL;
        }
        return (rc);
}

/*
 * Initiate cross call processing.
 */
static void
xc_common(
        xc_func_t func,
        xc_arg_t arg1,
        xc_arg_t arg2,
        xc_arg_t arg3,
        ulong_t *set,
        uint_t command)
{
        int c;
        struct cpu *cpup;
        xc_msg_t *msg;
        xc_data_t *data;
        int cnt;
        int save_spl;

        if (!xc_initialized) {
                if (BT_TEST(set, CPU->cpu_id) && (CPU->cpu_flags & CPU_READY) &&
                    func != NULL)
                        (void) (*func)(arg1, arg2, arg3);
                return;
        }

        save_spl = splr(ipltospl(XC_HI_PIL));

        /*
         * fill in cross call data
         */
        data = &CPU->cpu_m.xc_data;
        data->xc_func = func;
        data->xc_a1 = arg1;
        data->xc_a2 = arg2;
        data->xc_a3 = arg3;

        /*
         * Post messages to all CPUs involved that are CPU_READY
         */
        CPU->cpu_m.xc_wait_cnt = 0;
        for (c = 0; c < max_ncpus; ++c) {
                if (!BT_TEST(set, c))
                        continue;
                cpup = cpu[c];
                if (cpup == NULL || !(cpup->cpu_flags & CPU_READY))
                        continue;

                /*
                 * Fill out a new message.
                 */
                msg = xc_extract(&CPU->cpu_m.xc_free);
                if (msg == NULL)
                        panic("Ran out of free xc_msg_t's");
                msg->xc_command = command;
                if (msg->xc_master != CPU->cpu_id)
                        panic("msg %p has wrong xc_master", (void *)msg);
                msg->xc_slave = c;

                /*
                 * Increment my work count for all messages that I'll
                 * transition from DONE to FREE.
                 * Also remember how many XC_MSG_WAITINGs to look for
                 */
                (void) xc_increment(&CPU->cpu_m);
                if (command == XC_MSG_SYNC)
                        ++CPU->cpu_m.xc_wait_cnt;

                /*
                 * Increment the target CPU work count then insert the message
                 * in the target msgbox. If I post the first bit of work
                 * for the target to do, send an IPI to the target CPU.
                 */
                cnt = xc_increment(&cpup->cpu_m);
                xc_insert(&cpup->cpu_m.xc_msgbox, msg);
                if (cpup != CPU) {
                        if (cnt == 0) {
                                CPU_STATS_ADDQ(CPU, sys, xcalls, 1);
                                send_dirint(c, XC_HI_PIL);
                                if (xc_collect_enable)
                                        ++xc_total_cnt;
                        } else if (xc_collect_enable) {
                                ++xc_multi_cnt;
                        }
                }
        }

        /*
         * Now drop into the message handler until all work is done
         */
        (void) xc_serv(NULL, NULL);
        splx(save_spl);
}

/*
 * Push out a priority cross call.
 */
static void
xc_priority_common(
        xc_func_t func,
        xc_arg_t arg1,
        xc_arg_t arg2,
        xc_arg_t arg3,
        ulong_t *set)
{
        int i;
        int c;
        struct cpu *cpup;

        /*
         * Wait briefly for any previous xc_priority to have finished.
         */
        for (c = 0; c < max_ncpus; ++c) {
                cpup = cpu[c];
                if (cpup == NULL || !(cpup->cpu_flags & CPU_READY))
                        continue;

                /*
                 * The value of 40000 here is from old kernel code. It
                 * really should be changed to some time based value, since
                 * under a hypervisor, there's no guarantee a remote CPU
                 * is even scheduled.
                 */
                for (i = 0; BT_TEST(xc_priority_set, c) && i < 40000; ++i)
                        SMT_PAUSE();

                /*
                 * Some CPU did not respond to a previous priority request. It's
                 * probably deadlocked with interrupts blocked or some such
                 * problem. We'll just erase the previous request - which was
                 * most likely a kmdb_enter that has already expired - and plow
                 * ahead.
                 */
                if (BT_TEST(xc_priority_set, c)) {
                        BT_ATOMIC_CLEAR(xc_priority_set, c);
                        if (cpup->cpu_m.xc_work_cnt > 0)
                                xc_decrement(&cpup->cpu_m);
                }
        }

        /*
         * fill in cross call data
         */
        xc_priority_data.xc_func = func;
        xc_priority_data.xc_a1 = arg1;
        xc_priority_data.xc_a2 = arg2;
        xc_priority_data.xc_a3 = arg3;

        /*
         * Post messages to all CPUs involved that are CPU_READY
         * We'll always IPI, plus bang on the xc_msgbox for i86_mwait()
         */
        for (c = 0; c < max_ncpus; ++c) {
                if (!BT_TEST(set, c))
                        continue;
                cpup = cpu[c];
                if (cpup == NULL || !(cpup->cpu_flags & CPU_READY) ||
                    cpup == CPU)
                        continue;
                (void) xc_increment(&cpup->cpu_m);
                BT_ATOMIC_SET(xc_priority_set, c);
                send_dirint(c, XC_HI_PIL);
                for (i = 0; i < 10; ++i) {
                        (void) atomic_cas_ptr(&cpup->cpu_m.xc_msgbox,
                            cpup->cpu_m.xc_msgbox, cpup->cpu_m.xc_msgbox);
                }
        }
}

/*
 * Do cross call to all other CPUs with absolutely no waiting or handshaking.
 * This should only be used for extraordinary operations, like panic(), which
 * need to work, in some fashion, in a not completely functional system.
 * All other uses that want minimal waiting should use xc_call_nowait().
 */
void
xc_priority(
        xc_arg_t arg1,
        xc_arg_t arg2,
        xc_arg_t arg3,
        ulong_t *set,
        xc_func_t func)
{
        extern int IGNORE_KERNEL_PREEMPTION;
        int save_spl = splr(ipltospl(XC_HI_PIL));
        int save_kernel_preemption = IGNORE_KERNEL_PREEMPTION;

        IGNORE_KERNEL_PREEMPTION = 1;
        xc_priority_common((xc_func_t)func, arg1, arg2, arg3, set);
        IGNORE_KERNEL_PREEMPTION = save_kernel_preemption;
        splx(save_spl);
}

/*
 * Wrapper for kmdb to capture other CPUs, causing them to enter the debugger.
 */
void
kdi_xc_others(int this_cpu, void (*func)(void))
{
        extern int IGNORE_KERNEL_PREEMPTION;
        int save_kernel_preemption;
        cpuset_t set;

        if (!xc_initialized)
                return;

        save_kernel_preemption = IGNORE_KERNEL_PREEMPTION;
        IGNORE_KERNEL_PREEMPTION = 1;
        CPUSET_ALL_BUT(set, this_cpu);
        xc_priority_common((xc_func_t)func, 0, 0, 0, CPUSET2BV(set));
        IGNORE_KERNEL_PREEMPTION = save_kernel_preemption;
}



/*
 * Invoke function on specified processors. Remotes may continue after
 * service with no waiting. xc_call_nowait() may return immediately too.
 */
void
xc_call_nowait(
        xc_arg_t arg1,
        xc_arg_t arg2,
        xc_arg_t arg3,
        ulong_t *set,
        xc_func_t func)
{
        xc_common(func, arg1, arg2, arg3, set, XC_MSG_ASYNC);
}

/*
 * Invoke function on specified processors. Remotes may continue after
 * service with no waiting. xc_call() returns only after remotes have finished.
 */
void
xc_call(
        xc_arg_t arg1,
        xc_arg_t arg2,
        xc_arg_t arg3,
        ulong_t *set,
        xc_func_t func)
{
        xc_common(func, arg1, arg2, arg3, set, XC_MSG_CALL);
}

/*
 * Invoke function on specified processors. Remotes wait until all have
 * finished. xc_sync() also waits until all remotes have finished.
 */
void
xc_sync(
        xc_arg_t arg1,
        xc_arg_t arg2,
        xc_arg_t arg3,
        ulong_t *set,
        xc_func_t func)
{
        xc_common(func, arg1, arg2, arg3, set, XC_MSG_SYNC);
}