5285 pass in cpu_pause_func via pause_cpus

[unleashed.git] / usr / src / uts / i86xpv / os / mp_xen.c

/*
 * 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.
 */

/*
 * Virtual CPU management.
 *
 * VCPUs can be controlled in one of two ways; through the domain itself
 * (psradm, p_online(), etc.), and via changes in xenstore (vcpu_config()).
 * Unfortunately, the terminology is used in different ways; they work out as
 * follows:
 *
 * P_ONLINE: the VCPU is up and running, taking interrupts and running threads
 *
 * P_OFFLINE: the VCPU is up and running, but quiesced (i.e. blocked in the
 * hypervisor on the idle thread).  It must be up since a downed VCPU cannot
 * receive interrupts, and we require this for offline CPUs in Solaris.
 *
 * P_POWEROFF: the VCPU is down (we never called xen_vcpu_up(), or called
 * xen_vcpu_down() for it).  It can't take interrupts or run anything, though
 * if it has run previously, its software state (cpu_t, machcpu structures, IPI
 * event channels, etc.) will still exist.
 *
 * The hypervisor has two notions of CPU states as represented in the store:
 *
 * "offline": the VCPU is down.  Corresponds to P_POWEROFF.
 *
 * "online": the VCPU is running.  Corresponds to a CPU state other than
 * P_POWEROFF.
 *
 * Currently, only a notification via xenstore can bring a CPU into a
 * P_POWEROFF state, and only the domain can change between P_ONLINE, P_NOINTR,
 * P_OFFLINE, etc.  We need to be careful to treat xenstore notifications
 * idempotently, as we'll get 'duplicate' entries when we resume a domain.
 *
 * Note that the xenstore configuration is strictly advisory, in that a domain
 * can choose to ignore it and still power up a VCPU in the offline state. To
 * play nice, we don't allow it. Thus, any attempt to power on/off a CPU is
 * ENOTSUP from within Solaris.
 *
 * Powering off a VCPU and suspending the domain use similar code. The
 * difficulty here is that we must ensure that each VCPU is in a stable
 * state: it must have a saved PCB, and not be responding to interrupts
 * (since we are just about to remove its ability to run on a real CPU,
 * possibly forever).  However, an offline CPU in Solaris can take
 * cross-call interrupts, as mentioned, so we must go through a
 * two-stage process.  First, we use the standard Solaris pause_cpus().
 * This ensures that all CPUs are either in mach_cpu_pause() or
 * mach_cpu_idle(), and nothing will cross-call them.
 *
 * Powered-off-CPUs are already safe, as we own the cpu_lock needed to
 * bring them back up, and in state CPU_PHASE_POWERED_OFF.
 *
 * Running CPUs are spinning in mach_cpu_pause() waiting for either
 * PAUSE_IDLE or CPU_PHASE_WAIT_SAFE.
 *
 * Offline CPUs are either running the idle thread and periodically
 * checking for CPU_PHASE_WAIT_SAFE, or blocked in the hypervisor.
 *
 * Thus, we set CPU_PHASE_WAIT_SAFE for every powered-on CPU, as well as
 * poking them to make sure they're not blocked[1]. When every CPU has
 * responded by reaching a safe state and setting CPU_PHASE_SAFE, we
 * know we can suspend, or power-off a CPU, without problems.
 *
 * [1] note that we have to repeatedly poke offline CPUs: it's the only
 * way to ensure that the CPU doesn't miss the state change before
 * dropping into HYPERVISOR_block().
 */

#include <sys/types.h>
#include <sys/systm.h>
#include <sys/param.h>
#include <sys/taskq.h>
#include <sys/cmn_err.h>
#include <sys/archsystm.h>
#include <sys/machsystm.h>
#include <sys/segments.h>
#include <sys/cpuvar.h>
#include <sys/x86_archext.h>
#include <sys/controlregs.h>
#include <sys/hypervisor.h>
#include <sys/xpv_panic.h>
#include <sys/mman.h>
#include <sys/psw.h>
#include <sys/cpu.h>
#include <sys/sunddi.h>
#include <util/sscanf.h>
#include <vm/hat_i86.h>
#include <vm/hat.h>
#include <vm/as.h>

#include <xen/public/io/xs_wire.h>
#include <xen/sys/xenbus_impl.h>
#include <xen/public/vcpu.h>

extern cpuset_t cpu_ready_set;

#define CPU_PHASE_NONE 0
#define CPU_PHASE_WAIT_SAFE 1
#define CPU_PHASE_SAFE 2
#define CPU_PHASE_POWERED_OFF 3

/*
 * We can only poke CPUs during barrier enter 256 times a second at
 * most.
 */
#define POKE_TIMEOUT (NANOSEC / 256)

static taskq_t *cpu_config_tq;
static int cpu_phase[NCPU];

static void vcpu_config_event(struct xenbus_watch *, const char **, uint_t);
static int xen_vcpu_initialize(processorid_t, vcpu_guest_context_t *);

/*
 * Return whether or not the vcpu is actually running on a pcpu
 */
int
vcpu_on_pcpu(processorid_t cpu)
{
        struct vcpu_runstate_info runstate;
        int     ret = VCPU_STATE_UNKNOWN;

        ASSERT(cpu < NCPU);
        /*
         * Don't bother with hypercall if we are asking about ourself
         */
        if (cpu == CPU->cpu_id)
                return (VCPU_ON_PCPU);
        if (HYPERVISOR_vcpu_op(VCPUOP_get_runstate_info, cpu, &runstate) != 0)
                goto out;

        switch (runstate.state) {
        case RUNSTATE_running:
                ret = VCPU_ON_PCPU;
                break;

        case RUNSTATE_runnable:
        case RUNSTATE_offline:
        case RUNSTATE_blocked:
                ret = VCPU_NOT_ON_PCPU;
                break;

        default:
                break;
        }

out:
        return (ret);
}

/*
 * These routines allocate any global state that might be needed
 * while starting cpus.  For virtual cpus, there is no such state.
 */
int
mach_cpucontext_init(void)
{
        return (0);
}

void
do_cpu_config_watch(int state)
{
        static struct xenbus_watch cpu_config_watch;

        if (state != XENSTORE_UP)
                return;
        cpu_config_watch.node = "cpu";
        cpu_config_watch.callback = vcpu_config_event;
        if (register_xenbus_watch(&cpu_config_watch)) {
                taskq_destroy(cpu_config_tq);
                cmn_err(CE_WARN, "do_cpu_config_watch: "
                    "failed to set vcpu config watch");
        }

}

/*
 * This routine is called after all the "normal" MP startup has
 * been done; a good place to start watching xen store for virtual
 * cpu hot plug events.
 */
void
mach_cpucontext_fini(void)
{

        cpu_config_tq = taskq_create("vcpu config taskq", 1,
            maxclsyspri - 1, 1, 1, TASKQ_PREPOPULATE);

        (void) xs_register_xenbus_callback(do_cpu_config_watch);
}

/*
 * Fill in the remaining CPU context and initialize it.
 */
static int
mp_set_cpu_context(vcpu_guest_context_t *vgc, cpu_t *cp)
{
        uint_t vec, iopl;

        vgc->flags = VGCF_IN_KERNEL;

        /*
         * fpu_ctx we leave as zero; on first fault we'll store
         * sse_initial into it anyway.
         */

#if defined(__amd64)
        vgc->user_regs.cs = KCS_SEL | SEL_KPL;  /* force to ring 3 */
#else
        vgc->user_regs.cs = KCS_SEL;
#endif
        vgc->user_regs.ds = KDS_SEL;
        vgc->user_regs.es = KDS_SEL;
        vgc->user_regs.ss = KDS_SEL;
        vgc->kernel_ss = KDS_SEL;

        /*
         * Allow I/O privilege level for Dom0 kernel.
         */
        if (DOMAIN_IS_INITDOMAIN(xen_info))
                iopl = (PS_IOPL & 0x1000); /* ring 1 */
        else
                iopl = 0;

#if defined(__amd64)
        vgc->user_regs.fs = 0;
        vgc->user_regs.gs = 0;
        vgc->user_regs.rflags = F_OFF | iopl;
#elif defined(__i386)
        vgc->user_regs.fs = KFS_SEL;
        vgc->user_regs.gs = KGS_SEL;
        vgc->user_regs.eflags = F_OFF | iopl;
        vgc->event_callback_cs = vgc->user_regs.cs;
        vgc->failsafe_callback_cs = vgc->user_regs.cs;
#endif

        /*
         * Initialize the trap_info_t from the IDT
         */
#if !defined(__lint)
        ASSERT(NIDT == sizeof (vgc->trap_ctxt) / sizeof (vgc->trap_ctxt[0]));
#endif
        for (vec = 0; vec < NIDT; vec++) {
                trap_info_t *ti = &vgc->trap_ctxt[vec];

                if (xen_idt_to_trap_info(vec,
                    &cp->cpu_m.mcpu_idt[vec], ti) == 0) {
                        ti->cs = KCS_SEL;
                        ti->vector = vec;
                }
        }

        /*
         * No LDT
         */

        /*
         * (We assert in various places that the GDT is (a) aligned on a
         * page boundary and (b) one page long, so this really should fit..)
         */
#ifdef CRASH_XEN
        vgc->gdt_frames[0] = pa_to_ma(mmu_btop(cp->cpu_m.mcpu_gdtpa));
#else
        vgc->gdt_frames[0] = pfn_to_mfn(mmu_btop(cp->cpu_m.mcpu_gdtpa));
#endif
        vgc->gdt_ents = NGDT;

        vgc->ctrlreg[0] = CR0_ENABLE_FPU_FLAGS(getcr0());

#if defined(__i386)
        if (mmu.pae_hat)
                vgc->ctrlreg[3] =
                    xen_pfn_to_cr3(pfn_to_mfn(kas.a_hat->hat_htable->ht_pfn));
        else
#endif
                vgc->ctrlreg[3] =
                    pa_to_ma(mmu_ptob(kas.a_hat->hat_htable->ht_pfn));

        vgc->ctrlreg[4] = getcr4();

        vgc->event_callback_eip = (uintptr_t)xen_callback;
        vgc->failsafe_callback_eip = (uintptr_t)xen_failsafe_callback;
        vgc->flags |= VGCF_failsafe_disables_events;

#if defined(__amd64)
        /*
         * XXPV should this be moved to init_cpu_syscall?
         */
        vgc->syscall_callback_eip = (uintptr_t)sys_syscall;
        vgc->flags |= VGCF_syscall_disables_events;

        ASSERT(vgc->user_regs.gs == 0);
        vgc->gs_base_kernel = (uintptr_t)cp;
#endif

        return (xen_vcpu_initialize(cp->cpu_id, vgc));
}

/*
 * Create a guest virtual cpu context so that the virtual cpu
 * springs into life in the domain just about to call mp_startup()
 *
 * Virtual CPUs must be initialized once in the lifetime of the domain;
 * after that subsequent attempts to start them will fail with X_EEXIST.
 *
 * Thus 'alloc' -really- creates and initializes the virtual
 * CPU context just once. Once the initialisation succeeds, we never
 * free it, nor the regular cpu_t to which it refers.
 */
void *
mach_cpucontext_alloc(struct cpu *cp)
{
        kthread_t *tp = cp->cpu_thread;
        vcpu_guest_context_t vgc;

        int err = 1;

        /*
         * First, augment the incoming cpu structure
         * - vcpu pointer reference
         * - pending event storage area
         * - physical address of GDT
         */
        cp->cpu_m.mcpu_vcpu_info =
            &HYPERVISOR_shared_info->vcpu_info[cp->cpu_id];
        cp->cpu_m.mcpu_evt_pend = kmem_zalloc(
            sizeof (struct xen_evt_data), KM_SLEEP);
        cp->cpu_m.mcpu_gdtpa =
            mmu_ptob(hat_getpfnum(kas.a_hat, (caddr_t)cp->cpu_gdt));

        if ((err = xen_gdt_setprot(cp, PROT_READ)) != 0)
                goto done;

        /*
         * Now set up the vcpu context so that we can start this vcpu
         * in the kernel at tp->t_pc (mp_startup).  Note that the
         * thread will thread_exit() shortly after performing the
         * initialization; in particular, we will *never* take a
         * privilege transition on this thread.
         */

        bzero(&vgc, sizeof (vgc));

#ifdef __amd64
        vgc.user_regs.rip = tp->t_pc;
        vgc.user_regs.rsp = tp->t_sp;
        vgc.user_regs.rbp = tp->t_sp - 2 * sizeof (greg_t);
#else
        vgc.user_regs.eip = tp->t_pc;
        vgc.user_regs.esp = tp->t_sp;
        vgc.user_regs.ebp = tp->t_sp - 2 * sizeof (greg_t);
#endif
        /*
         * XXPV Fix resume, if Russ didn't already fix it.
         *
         * Note that resume unconditionally puts t->t_stk + sizeof (regs)
         * into kernel_sp via HYPERVISOR_stack_switch. This anticipates
         * that only lwps take traps that switch to the kernel stack;
         * part of creating an lwp adjusts the stack by subtracting
         * sizeof (struct regs) off t_stk.
         *
         * The more interesting question is, why do we do all the work
         * of a fully fledged lwp for a plain thread?  In particular
         * we don't have to call HYPERVISOR_stack_switch for lwp-less threads
         * or futz with the LDT.  This should probably all be done with
         * an lwp context operator to keep pure thread context switch fast.
         */
        vgc.kernel_sp = (ulong_t)tp->t_stk;

        err = mp_set_cpu_context(&vgc, cp);

done:
        if (err) {
                mach_cpucontext_free(cp, NULL, err);
                return (NULL);
        }
        return (cp);
}

/*
 * By the time we are called either we have successfully started
 * the cpu, or our attempt to start it has failed.
 */

/*ARGSUSED*/
void
mach_cpucontext_free(struct cpu *cp, void *arg, int err)
{
        switch (err) {
        case 0:
                break;
        case ETIMEDOUT:
                /*
                 * The vcpu context is loaded into the hypervisor, and
                 * we've tried to start it, but the vcpu has not been set
                 * running yet, for whatever reason.  We arrange to -not-
                 * free any data structures it may be referencing.  In
                 * particular, we've already told the hypervisor about
                 * the GDT, and so we can't map it read-write again.
                 */
                break;
        default:
                (void) xen_gdt_setprot(cp, PROT_READ | PROT_WRITE);
                kmem_free(cp->cpu_m.mcpu_evt_pend,
                    sizeof (struct xen_evt_data));
                break;
        }
}

/*
 * Reset this CPU's context.  Clear out any pending evtchn data, since event
 * channel numbers will all change when we resume.
 */
void
mach_cpucontext_reset(cpu_t *cp)
{
        bzero(cp->cpu_m.mcpu_evt_pend, sizeof (struct xen_evt_data));
        /* mcpu_intr_pending ? */
}

static void
pcb_to_user_regs(label_t *pcb, vcpu_guest_context_t *vgc)
{
#ifdef __amd64
        vgc->user_regs.rip = pcb->val[REG_LABEL_PC];
        vgc->user_regs.rsp = pcb->val[REG_LABEL_SP];
        vgc->user_regs.rbp = pcb->val[REG_LABEL_BP];
        vgc->user_regs.rbx = pcb->val[REG_LABEL_RBX];
        vgc->user_regs.r12 = pcb->val[REG_LABEL_R12];
        vgc->user_regs.r13 = pcb->val[REG_LABEL_R13];
        vgc->user_regs.r14 = pcb->val[REG_LABEL_R14];
        vgc->user_regs.r15 = pcb->val[REG_LABEL_R15];
#else /* __amd64 */
        vgc->user_regs.eip = pcb->val[REG_LABEL_PC];
        vgc->user_regs.esp = pcb->val[REG_LABEL_SP];
        vgc->user_regs.ebp = pcb->val[REG_LABEL_BP];
        vgc->user_regs.ebx = pcb->val[REG_LABEL_EBX];
        vgc->user_regs.esi = pcb->val[REG_LABEL_ESI];
        vgc->user_regs.edi = pcb->val[REG_LABEL_EDI];
#endif /* __amd64 */
}

/*
 * Restore the context of a CPU during resume.  This context is always
 * inside enter_safe_phase(), below.
 */
void
mach_cpucontext_restore(cpu_t *cp)
{
        vcpu_guest_context_t vgc;
        int err;

        ASSERT(cp->cpu_thread == cp->cpu_pause_thread ||
            cp->cpu_thread == cp->cpu_idle_thread);

        bzero(&vgc, sizeof (vgc));

        pcb_to_user_regs(&cp->cpu_thread->t_pcb, &vgc);

        /*
         * We're emulating a longjmp() here: in particular, we need to bump the
         * stack pointer to account for the pop of xIP that returning from
         * longjmp() normally would do, and set the return value in xAX to 1.
         */
#ifdef __amd64
        vgc.user_regs.rax = 1;
        vgc.user_regs.rsp += sizeof (ulong_t);
#else
        vgc.user_regs.eax = 1;
        vgc.user_regs.esp += sizeof (ulong_t);
#endif

        vgc.kernel_sp = cp->cpu_thread->t_sp;

        err = mp_set_cpu_context(&vgc, cp);

        ASSERT(err == 0);
}

/*
 * Reach a point at which the CPU can be safely powered-off or
 * suspended.  Nothing can wake this CPU out of the loop.
 */
static void
enter_safe_phase(void)
{
        ulong_t flags = intr_clear();

        if (setjmp(&curthread->t_pcb) == 0) {
                cpu_phase[CPU->cpu_id] = CPU_PHASE_SAFE;
                while (cpu_phase[CPU->cpu_id] == CPU_PHASE_SAFE)
                        SMT_PAUSE();
        }

        ASSERT(!interrupts_enabled());

        intr_restore(flags);
}

/*
 * Offline CPUs run this code even under a pause_cpus(), so we must
 * check if we need to enter the safe phase.
 */
void
mach_cpu_idle(void)
{
        if (IN_XPV_PANIC()) {
                xpv_panic_halt();
        } else  {
                (void) HYPERVISOR_block();
                if (cpu_phase[CPU->cpu_id] == CPU_PHASE_WAIT_SAFE)
                        enter_safe_phase();
        }
}

/*
 * Spin until either start_cpus() wakes us up, or we get a request to
 * enter the safe phase (followed by a later start_cpus()).
 */
void
mach_cpu_pause(volatile char *safe)
{
        *safe = PAUSE_WAIT;
        membar_enter();

        while (*safe != PAUSE_IDLE) {
                if (cpu_phase[CPU->cpu_id] == CPU_PHASE_WAIT_SAFE)
                        enter_safe_phase();
                SMT_PAUSE();
        }
}

void
mach_cpu_halt(char *msg)
{
        if (msg)
                prom_printf("%s\n", msg);
        (void) xen_vcpu_down(CPU->cpu_id);
}

/*ARGSUSED*/
int
mp_cpu_poweron(struct cpu *cp)
{
        return (ENOTSUP);
}

/*ARGSUSED*/
int
mp_cpu_poweroff(struct cpu *cp)
{
        return (ENOTSUP);
}

void
mp_enter_barrier(void)
{
        hrtime_t last_poke_time = 0;
        int poke_allowed = 0;
        int done = 0;
        int i;

        ASSERT(MUTEX_HELD(&cpu_lock));

        pause_cpus(NULL, NULL);

        while (!done) {
                done = 1;
                poke_allowed = 0;

                if (xpv_gethrtime() - last_poke_time > POKE_TIMEOUT) {
                        last_poke_time = xpv_gethrtime();
                        poke_allowed = 1;
                }

                for (i = 0; i < NCPU; i++) {
                        cpu_t *cp = cpu_get(i);

                        if (cp == NULL || cp == CPU)
                                continue;

                        switch (cpu_phase[i]) {
                        case CPU_PHASE_NONE:
                                cpu_phase[i] = CPU_PHASE_WAIT_SAFE;
                                poke_cpu(i);
                                done = 0;
                                break;

                        case CPU_PHASE_WAIT_SAFE:
                                if (poke_allowed)
                                        poke_cpu(i);
                                done = 0;
                                break;

                        case CPU_PHASE_SAFE:
                        case CPU_PHASE_POWERED_OFF:
                                break;
                        }
                }

                SMT_PAUSE();
        }
}

void
mp_leave_barrier(void)
{
        int i;

        ASSERT(MUTEX_HELD(&cpu_lock));

        for (i = 0; i < NCPU; i++) {
                cpu_t *cp = cpu_get(i);

                if (cp == NULL || cp == CPU)
                        continue;

                switch (cpu_phase[i]) {
                /*
                 * If we see a CPU in one of these phases, something has
                 * gone badly wrong with the guarantees
                 * mp_enter_barrier() is supposed to provide.  Rather
                 * than attempt to stumble along (and since we can't
                 * panic properly in this context), we tell the
                 * hypervisor we've crashed.
                 */
                case CPU_PHASE_NONE:
                case CPU_PHASE_WAIT_SAFE:
                        (void) HYPERVISOR_shutdown(SHUTDOWN_crash);
                        break;

                case CPU_PHASE_POWERED_OFF:
                        break;

                case CPU_PHASE_SAFE:
                        cpu_phase[i] = CPU_PHASE_NONE;
                }
        }

        start_cpus();
}

static int
poweroff_vcpu(struct cpu *cp)
{
        int error;

        ASSERT(MUTEX_HELD(&cpu_lock));

        ASSERT(CPU->cpu_id != cp->cpu_id);
        ASSERT(cp->cpu_flags & CPU_QUIESCED);

        mp_enter_barrier();

        if ((error = xen_vcpu_down(cp->cpu_id)) == 0) {
                ASSERT(cpu_phase[cp->cpu_id] == CPU_PHASE_SAFE);

                CPUSET_DEL(cpu_ready_set, cp->cpu_id);

                cp->cpu_flags |= CPU_POWEROFF | CPU_OFFLINE;
                cp->cpu_flags &=
                    ~(CPU_RUNNING | CPU_READY | CPU_EXISTS | CPU_ENABLE);

                cpu_phase[cp->cpu_id] = CPU_PHASE_POWERED_OFF;

                cpu_set_state(cp);
        }

        mp_leave_barrier();

        return (error);
}

static int
vcpu_config_poweroff(processorid_t id)
{
        int oldstate;
        int error;
        cpu_t *cp;

        mutex_enter(&cpu_lock);

        if ((cp = cpu_get(id)) == NULL) {
                mutex_exit(&cpu_lock);
                return (ESRCH);
        }

        if (cpu_get_state(cp) == P_POWEROFF) {
                mutex_exit(&cpu_lock);
                return (0);
        }

        mutex_exit(&cpu_lock);

        do {
                error = p_online_internal(id, P_OFFLINE,
                    &oldstate);

                if (error != 0)
                        break;

                /*
                 * So we just changed it to P_OFFLINE.  But then we dropped
                 * cpu_lock, so now it is possible for another thread to change
                 * the cpu back to a different, non-quiesced state e.g.
                 * P_ONLINE.
                 */
                mutex_enter(&cpu_lock);
                if ((cp = cpu_get(id)) == NULL)
                        error = ESRCH;
                else {
                        if (cp->cpu_flags & CPU_QUIESCED)
                                error = poweroff_vcpu(cp);
                        else
                                error = EBUSY;
                }
                mutex_exit(&cpu_lock);
        } while (error == EBUSY);

        return (error);
}

/*
 * Add a new virtual cpu to the domain.
 */
static int
vcpu_config_new(processorid_t id)
{
        extern int start_cpu(processorid_t);
        int error;

        if (ncpus == 1) {
                printf("cannot (yet) add cpus to a single-cpu domain\n");
                return (ENOTSUP);
        }

        affinity_set(CPU_CURRENT);
        error = start_cpu(id);
        affinity_clear();
        return (error);
}

static int
poweron_vcpu(struct cpu *cp)
{
        int error;

        ASSERT(MUTEX_HELD(&cpu_lock));

        if (HYPERVISOR_vcpu_op(VCPUOP_is_up, cp->cpu_id, NULL) != 0) {
                printf("poweron_vcpu: vcpu%d is not available!\n",
                    cp->cpu_id);
                return (ENXIO);
        }

        if ((error = xen_vcpu_up(cp->cpu_id)) == 0) {
                CPUSET_ADD(cpu_ready_set, cp->cpu_id);
                cp->cpu_flags |= CPU_EXISTS | CPU_READY | CPU_RUNNING;
                cp->cpu_flags &= ~CPU_POWEROFF;
                /*
                 * There are some nasty races possible here.
                 * Tell the vcpu it's up one more time.
                 * XXPV Is this enough?  Is this safe?
                 */
                (void) xen_vcpu_up(cp->cpu_id);

                cpu_phase[cp->cpu_id] = CPU_PHASE_NONE;

                cpu_set_state(cp);
        }
        return (error);
}

static int
vcpu_config_poweron(processorid_t id)
{
        cpu_t *cp;
        int oldstate;
        int error;

        if (id >= ncpus)
                return (vcpu_config_new(id));

        mutex_enter(&cpu_lock);

        if ((cp = cpu_get(id)) == NULL) {
                mutex_exit(&cpu_lock);
                return (ESRCH);
        }

        if (cpu_get_state(cp) != P_POWEROFF) {
                mutex_exit(&cpu_lock);
                return (0);
        }

        if ((error = poweron_vcpu(cp)) != 0) {
                mutex_exit(&cpu_lock);
                return (error);
        }

        mutex_exit(&cpu_lock);

        return (p_online_internal(id, P_ONLINE, &oldstate));
}

#define REPORT_LEN      128

static void
vcpu_config_report(processorid_t id, uint_t newstate, int error)
{
        char *report = kmem_alloc(REPORT_LEN, KM_SLEEP);
        size_t len;
        char *ps;

        switch (newstate) {
        case P_ONLINE:
                ps = PS_ONLINE;
                break;
        case P_POWEROFF:
                ps = PS_POWEROFF;
                break;
        default:
                cmn_err(CE_PANIC, "unknown state %u\n", newstate);
                break;
        }

        len = snprintf(report, REPORT_LEN,
            "cpu%d: externally initiated %s", id, ps);

        if (!error) {
                cmn_err(CE_CONT, "!%s\n", report);
                kmem_free(report, REPORT_LEN);
                return;
        }

        len += snprintf(report + len, REPORT_LEN - len,
            " failed, error %d: ", error);
        switch (error) {
        case EEXIST:
                len += snprintf(report + len, REPORT_LEN - len,
                    "cpu already %s", ps ? ps : "?");
                break;
        case ESRCH:
                len += snprintf(report + len, REPORT_LEN - len,
                    "cpu not found");
                break;
        case EINVAL:
        case EALREADY:
                break;
        case EPERM:
                len += snprintf(report + len, REPORT_LEN - len,
                    "insufficient privilege (0x%x)", id);
                break;
        case EBUSY:
                switch (newstate) {
                case P_ONLINE:
                        /*
                         * This return comes from mp_cpu_start -
                         * we cannot 'start' the boot CPU.
                         */
                        len += snprintf(report + len, REPORT_LEN - len,
                            "already running");
                        break;
                case P_POWEROFF:
                        len += snprintf(report + len, REPORT_LEN - len,
                            "bound lwps?");
                        break;
                default:
                        break;
                }
        default:
                break;
        }

        cmn_err(CE_CONT, "%s\n", report);
        kmem_free(report, REPORT_LEN);
}

static void
vcpu_config(void *arg)
{
        int id = (int)(uintptr_t)arg;
        int error;
        char dir[16];
        char *state;

        if ((uint_t)id >= max_ncpus) {
                cmn_err(CE_WARN,
                    "vcpu_config: cpu%d does not fit in this domain", id);
                return;
        }

        (void) snprintf(dir, sizeof (dir), "cpu/%d", id);
        state = kmem_alloc(MAXPATHLEN, KM_SLEEP);
        if (xenbus_scanf(XBT_NULL, dir, "availability", "%s", state) == 0) {
                if (strcmp(state, "online") == 0) {
                        error = vcpu_config_poweron(id);
                        vcpu_config_report(id, P_ONLINE, error);
                } else if (strcmp(state, "offline") == 0) {
                        error = vcpu_config_poweroff(id);
                        vcpu_config_report(id, P_POWEROFF, error);
                } else {
                        cmn_err(CE_WARN,
                            "cpu%d: unknown target state '%s'", id, state);
                }
        } else
                cmn_err(CE_WARN,
                    "cpu%d: unable to read target state from xenstore", id);

        kmem_free(state, MAXPATHLEN);
}

/*ARGSUSED*/
static void
vcpu_config_event(struct xenbus_watch *watch, const char **vec, uint_t len)
{
        const char *path = vec[XS_WATCH_PATH];
        processorid_t id;
        char *s;

        if ((s = strstr(path, "cpu/")) != NULL &&
            sscanf(s, "cpu/%d", &id) == 1) {
                /*
                 * Run the virtual CPU configuration on a separate thread to
                 * avoid blocking on this event for too long (and for now,
                 * to ensure configuration requests are serialized.)
                 */
                (void) taskq_dispatch(cpu_config_tq,
                    vcpu_config, (void *)(uintptr_t)id, 0);
        }
}

static int
xen_vcpu_initialize(processorid_t id, vcpu_guest_context_t *vgc)
{
        int err;

        if ((err = HYPERVISOR_vcpu_op(VCPUOP_initialise, id, vgc)) != 0) {
                char *str;
                int level = CE_WARN;

                switch (err) {
                case -X_EINVAL:
                        /*
                         * This interface squashes multiple error sources
                         * to one error code.  In particular, an X_EINVAL
                         * code can mean:
                         *
                         * -    the vcpu id is out of range
                         * -    cs or ss are in ring 0
                         * -    cr3 is wrong
                         * -    an entry in the new gdt is above the
                         *      reserved entry
                         * -    a frame underneath the new gdt is bad
                         */
                        str = "something is wrong :(";
                        break;
                case -X_ENOENT:
                        str = "no such cpu";
                        break;
                case -X_ENOMEM:
                        str = "no mem to copy ctxt";
                        break;
                case -X_EFAULT:
                        str = "bad address";
                        break;
                case -X_EEXIST:
                        /*
                         * Hmm.  This error is returned if the vcpu has already
                         * been initialized once before in the lifetime of this
                         * domain.  This is a logic error in the kernel.
                         */
                        level = CE_PANIC;
                        str = "already initialized";
                        break;
                default:
                        level = CE_PANIC;
                        str = "<unexpected>";
                        break;
                }

                cmn_err(level, "vcpu%d: failed to init: error %d: %s",
                    id, -err, str);
        }
        return (err);
}

long
xen_vcpu_up(processorid_t id)
{
        long err;

        if ((err = HYPERVISOR_vcpu_op(VCPUOP_up, id, NULL)) != 0) {
                char *str;

                switch (err) {
                case -X_ENOENT:
                        str = "no such cpu";
                        break;
                case -X_EINVAL:
                        /*
                         * Perhaps this is diagnostic overkill.
                         */
                        if (HYPERVISOR_vcpu_op(VCPUOP_is_up, id, NULL) < 0)
                                str = "bad cpuid";
                        else
                                str = "not initialized";
                        break;
                default:
                        str = "<unexpected>";
                        break;
                }

                printf("vcpu%d: failed to start: error %d: %s\n",
                    id, -(int)err, str);
                return (EBFONT);        /* deliberately silly */
        }
        return (err);
}

long
xen_vcpu_down(processorid_t id)
{
        long err;

        if ((err = HYPERVISOR_vcpu_op(VCPUOP_down, id, NULL)) != 0) {
                /*
                 * X_ENOENT:    no such cpu
                 * X_EINVAL:    bad cpuid
                 */
                panic("vcpu%d: failed to stop: error %d", id, -(int)err);
        }

        return (err);
}