ia32/os/sysi86.c

	sysi86.c revision 7af88ac71631ebf259c6c4c22a9f649ddff3e270
/*
 * 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 (c) 1992, 2010, Oracle and/or its affiliates. All rights reserved.
 */

/*  Copyright (c) 1990, 1991 UNIX System Laboratories, Inc. */
/*  Copyright (c) 1984, 1986, 1987, 1988, 1989, 1990 AT&T   */
/*    All Rights Reserved   */

/*  Copyright (c) 1987, 1988 Microsoft Corporation  */
/*    All Rights Reserved   */

#include <sys/param.h>
#include <sys/types.h>
#include <sys/sysmacros.h>
#include <sys/systm.h>
#include <sys/signal.h>
#include <sys/errno.h>
#include <sys/fault.h>
#include <sys/syscall.h>
#include <sys/cpuvar.h>
#include <sys/sysi86.h>
#include <sys/psw.h>
#include <sys/cred.h>
#include <sys/policy.h>
#include <sys/thread.h>
#include <sys/debug.h>
#include <sys/ontrap.h>
#include <sys/privregs.h>
#include <sys/x86_archext.h>
#include <sys/vmem.h>
#include <sys/kmem.h>
#include <sys/mman.h>
#include <sys/archsystm.h>
#include <vm/hat.h>
#include <vm/as.h>
#include <vm/seg.h>
#include <vm/seg_kmem.h>
#include <vm/faultcode.h>
#include <sys/fp.h>
#include <sys/cmn_err.h>
#include <sys/segments.h>
#include <sys/clock.h>
#if defined(__xpv)
#include <sys/hypervisor.h>
#include <sys/note.h>
#endif

static void ldt_alloc(proc_t *, uint_t);
static void ldt_free(proc_t *);
static void ldt_dup(proc_t *, proc_t *);
static void ldt_grow(proc_t *, uint_t);

/*
 * sysi86 System Call
 */

/* ARGSUSED */
int
sysi86(short cmd, uintptr_t arg1, uintptr_t arg2, uintptr_t arg3)
{
    struct ssd ssd;
    int error = 0;
    int c;
    proc_t *pp = curproc;

    switch (cmd) {

    /*
     * The SI86V86 subsystem call of the SYSI86 system call
     * supports only one subcode -- V86SC_IOPL.
     */
    case SI86V86:
        if (arg1 == V86SC_IOPL) {
            struct regs *rp = lwptoregs(ttolwp(curthread));
            greg_t oldpl = rp->r_ps & PS_IOPL;
            greg_t newpl = arg2 & PS_IOPL;

            /*
             * Must be privileged to run this system call
             * if giving more io privilege.
             */
            if (newpl > oldpl && (error =
                secpolicy_sys_config(CRED(), B_FALSE)) != 0)
                return (set_errno(error));
#if defined(__xpv)
            kpreempt_disable();
            installctx(curthread, NULL, xen_disable_user_iopl,
                xen_enable_user_iopl, NULL, NULL,
                xen_disable_user_iopl, NULL);
            xen_enable_user_iopl();
            kpreempt_enable();
#else
            rp->r_ps ^= oldpl ^ newpl;
#endif
        } else
            error = EINVAL;
        break;

    /*
     * Set a segment descriptor
     */
    case SI86DSCR:
        /*
         * There are considerable problems here manipulating
         * resources shared by many running lwps.  Get everyone
         * into a safe state before changing the LDT.
         */
        if (curthread != pp->p_agenttp && !holdlwps(SHOLDFORK1)) {
            error = EINTR;
            break;
        }

        if (get_udatamodel() == DATAMODEL_LP64) {
            error = EINVAL;
            break;
        }

        if (copyin((caddr_t)arg1, &ssd, sizeof (ssd)) < 0) {
            error = EFAULT;
            break;
        }

        error = setdscr(&ssd);

        mutex_enter(&pp->p_lock);
        if (curthread != pp->p_agenttp)
            continuelwps(pp);
        mutex_exit(&pp->p_lock);
        break;

    case SI86FPHW:
        c = fp_kind & 0xff;
        if (suword32((void *)arg1, c) == -1)
            error = EFAULT;
        break;

    case SI86FPSTART:
        /*
         * arg1 is the address of _fp_hw
         * arg2 is the desired x87 FCW value
         * arg3 is the desired SSE MXCSR value
         * a return value of one means SSE hardware, else none.
         */
        c = fp_kind & 0xff;
        if (suword32((void *)arg1, c) == -1) {
            error = EFAULT;
            break;
        }
        fpsetcw((uint16_t)arg2, (uint32_t)arg3);
        return ((fp_kind & __FP_SSE) ? 1 : 0);

    /* real time clock management commands */

    case WTODC:
        if ((error = secpolicy_settime(CRED())) == 0) {
            timestruc_t ts;
            mutex_enter(&tod_lock);
            gethrestime(&ts);
            tod_set(ts);
            mutex_exit(&tod_lock);
        }
        break;

/* Give some timezone playing room */
#define ONEWEEK (7 * 24 * 60 * 60)

    case SGMTL:
        /*
         * Called from 32 bit land, negative values
         * are not sign extended, so we do that here
         * by casting it to an int and back.  We also
         * clamp the value to within reason and detect
         * when a 64 bit call overflows an int.
         */
        if ((error = secpolicy_settime(CRED())) == 0) {
            int newlag = (int)arg1;

#ifdef _SYSCALL32_IMPL
            if (get_udatamodel() == DATAMODEL_NATIVE &&
                (long)newlag != (long)arg1) {
                error = EOVERFLOW;
            } else
#endif
            if (newlag >= -ONEWEEK && newlag <= ONEWEEK)
                sgmtl(newlag);
            else
                error = EOVERFLOW;
        }
        break;

    case GGMTL:
        if (get_udatamodel() == DATAMODEL_NATIVE) {
            if (sulword((void *)arg1, ggmtl()) == -1)
                error = EFAULT;
#ifdef _SYSCALL32_IMPL
        } else {
            time_t gmtl;

            if ((gmtl = ggmtl()) > INT32_MAX) {
                /*
                 * Since gmt_lag can at most be
                 * +/- 12 hours, something is
                 * *seriously* messed up here.
                 */
                error = EOVERFLOW;
            } else if (suword32((void *)arg1, (int32_t)gmtl) == -1)
                error = EFAULT;
#endif
        }
        break;

    case RTCSYNC:
        if ((error = secpolicy_settime(CRED())) == 0)
            rtcsync();
        break;

    /* END OF real time clock management commands */

    default:
        error = EINVAL;
        break;
    }
    return (error == 0 ? 0 : set_errno(error));
}

void
usd_to_ssd(user_desc_t *usd, struct ssd *ssd, selector_t sel)
{
    ssd->bo = USEGD_GETBASE(usd);
    ssd->ls = USEGD_GETLIMIT(usd);
    ssd->sel = sel;

    /*
     * set type, dpl and present bits.
     */
    ssd->acc1 = usd->usd_type;
    ssd->acc1 |= usd->usd_dpl << 5;
    ssd->acc1 |= usd->usd_p << (5 + 2);

    /*
     * set avl, DB and granularity bits.
     */
    ssd->acc2 = usd->usd_avl;

#if defined(__amd64)
    ssd->acc2 |= usd->usd_long << 1;
#else
    ssd->acc2 |= usd->usd_reserved << 1;
#endif

    ssd->acc2 |= usd->usd_def32 << (1 + 1);
    ssd->acc2 |= usd->usd_gran << (1 + 1 + 1);
}

static void
ssd_to_usd(struct ssd *ssd, user_desc_t *usd)
{

    ASSERT(bcmp(usd, &null_udesc, sizeof (*usd)) == 0);

    USEGD_SETBASE(usd, ssd->bo);
    USEGD_SETLIMIT(usd, ssd->ls);

    /*
     * set type, dpl and present bits.
     */
    usd->usd_type = ssd->acc1;
    usd->usd_dpl = ssd->acc1 >> 5;
    usd->usd_p = ssd->acc1 >> (5 + 2);

    ASSERT(usd->usd_type >= SDT_MEMRO);
    ASSERT(usd->usd_dpl == SEL_UPL);

    /*
     * 64-bit code selectors are never allowed in the LDT.
     * Reserved bit is always 0 on 32-bit sytems.
     */
#if defined(__amd64)
    usd->usd_long = 0;
#else
    usd->usd_reserved = 0;
#endif

    /*
     * set avl, DB and granularity bits.
     */
    usd->usd_avl = ssd->acc2;
    usd->usd_def32 = ssd->acc2 >> (1 + 1);
    usd->usd_gran = ssd->acc2 >> (1 + 1 + 1);
}


#if defined(__i386)

static void
ssd_to_sgd(struct ssd *ssd, gate_desc_t *sgd)
{

    ASSERT(bcmp(sgd, &null_sdesc, sizeof (*sgd)) == 0);

    sgd->sgd_looffset = ssd->bo;
    sgd->sgd_hioffset = ssd->bo >> 16;

    sgd->sgd_selector = ssd->ls;

    /*
     * set type, dpl and present bits.
     */
    sgd->sgd_type = ssd->acc1;
    sgd->sgd_dpl = ssd->acc1 >> 5;
    sgd->sgd_p = ssd->acc1 >> 7;
    ASSERT(sgd->sgd_type == SDT_SYSCGT);
    ASSERT(sgd->sgd_dpl == SEL_UPL);
    sgd->sgd_stkcpy = 0;
}

#endif  /* __i386 */

/*
 * Load LDT register with the current process's LDT.
 */
static void
ldt_load(void)
{
#if defined(__xpv)
    xen_set_ldt(get_ssd_base(&curproc->p_ldt_desc),
        curproc->p_ldtlimit + 1);
#else
    *((system_desc_t *)&CPU->cpu_gdt[GDT_LDT]) = curproc->p_ldt_desc;
    wr_ldtr(ULDT_SEL);
#endif
}

/*
 * Store a NULL selector in the LDTR. All subsequent illegal references to
 * the LDT will result in a #gp.
 */
void
ldt_unload(void)
{
#if defined(__xpv)
    xen_set_ldt(NULL, 0);
#else
    *((system_desc_t *)&CPU->cpu_gdt[GDT_LDT]) = null_sdesc;
    wr_ldtr(0);
#endif
}

/*ARGSUSED*/
static void
ldt_savectx(proc_t *p)
{
    ASSERT(p->p_ldt != NULL);
    ASSERT(p == curproc);

#if defined(__amd64)
    /*
     * The 64-bit kernel must be sure to clear any stale ldt
     * selectors when context switching away from a process that
     * has a private ldt. Consider the following example:
     *
     *  Wine creats a ldt descriptor and points a segment register
     *  to it.
     *
     *  We then context switch away from wine lwp to kernel
     *  thread and hit breakpoint in kernel with kmdb
     *
     *  When we continue and resume from kmdb we will #gp
     *  fault since kmdb will have saved the stale ldt selector
     *  from wine and will try to restore it but we are no longer in
     *  the context of the wine process and do not have our
     *  ldtr register pointing to the private ldt.
     */
    reset_sregs();
#endif

    ldt_unload();
    cpu_fast_syscall_enable(NULL);
}

static void
ldt_restorectx(proc_t *p)
{
    ASSERT(p->p_ldt != NULL);
    ASSERT(p == curproc);

    ldt_load();
    cpu_fast_syscall_disable(NULL);
}

/*
 * When a process with a private LDT execs, fast syscalls must be enabled for
 * the new process image.
 */
/* ARGSUSED */
static void
ldt_freectx(proc_t *p, int isexec)
{
    ASSERT(p->p_ldt);

    if (isexec) {
        kpreempt_disable();
        cpu_fast_syscall_enable(NULL);
        kpreempt_enable();
    }

    /*
     * ldt_free() will free the memory used by the private LDT, reset the
     * process's descriptor, and re-program the LDTR.
     */
    ldt_free(p);
}

/*
 * Install ctx op that ensures syscall/sysenter are disabled.
 * See comments below.
 *
 * When a thread with a private LDT forks, the new process
 * must have the LDT context ops installed.
 */
/* ARGSUSED */
static void
ldt_installctx(proc_t *p, proc_t *cp)
{
    proc_t      *targ = p;
    kthread_t   *t;

    /*
     * If this is a fork, operate on the child process.
     */
    if (cp != NULL) {
        targ = cp;
        ldt_dup(p, cp);
    }

    /*
     * The process context ops expect the target process as their argument.
     */
    ASSERT(removepctx(targ, targ, ldt_savectx, ldt_restorectx,
        ldt_installctx, ldt_savectx, ldt_freectx) == 0);

    installpctx(targ, targ, ldt_savectx, ldt_restorectx,
        ldt_installctx, ldt_savectx, ldt_freectx);

    /*
     * We've just disabled fast system call and return instructions; take
     * the slow path out to make sure we don't try to use one to return
     * back to user. We must set t_post_sys for every thread in the
     * process to make sure none of them escape out via fast return.
     */

    mutex_enter(&targ->p_lock);
    t = targ->p_tlist;
    do {
        t->t_post_sys = 1;
    } while ((t = t->t_forw) != targ->p_tlist);
    mutex_exit(&targ->p_lock);
}

int
setdscr(struct ssd *ssd)
{
    ushort_t seli;      /* selector index */
    user_desc_t *ldp;   /* descriptor pointer */
    user_desc_t ndesc;  /* new descriptor */
    proc_t  *pp = ttoproc(curthread);
    int rc = 0;

    /*
     * LDT segments: executable and data at DPL 3 only.
     */
    if (!SELISLDT(ssd->sel) || !SELISUPL(ssd->sel))
        return (EINVAL);

    /*
     * check the selector index.
     */
    seli = SELTOIDX(ssd->sel);
    if (seli >= MAXNLDT || seli < LDT_UDBASE)
        return (EINVAL);

    ndesc = null_udesc;
    mutex_enter(&pp->p_ldtlock);

    /*
     * If this is the first time for this process then setup a
     * private LDT for it.
     */
    if (pp->p_ldt == NULL) {
        ldt_alloc(pp, seli);

        /*
         * Now that this process has a private LDT, the use of
         * the syscall/sysret and sysenter/sysexit instructions
         * is forbidden for this processes because they destroy
         * the contents of %cs and %ss segment registers.
         *
         * Explicity disable them here and add a context handler
         * to the process. Note that disabling
         * them here means we can't use sysret or sysexit on
         * the way out of this system call - so we force this
         * thread to take the slow path (which doesn't make use
         * of sysenter or sysexit) back out.
         */
        kpreempt_disable();
        ldt_installctx(pp, NULL);
        cpu_fast_syscall_disable(NULL);
        ASSERT(curthread->t_post_sys != 0);
        kpreempt_enable();

    } else if (seli > pp->p_ldtlimit) {

        /*
         * Increase size of ldt to include seli.
         */
        ldt_grow(pp, seli);
    }

    ASSERT(seli <= pp->p_ldtlimit);
    ldp = &pp->p_ldt[seli];

    /*
     * On the 64-bit kernel, this is where things get more subtle.
     * Recall that in the 64-bit kernel, when we enter the kernel we
     * deliberately -don't- reload the segment selectors we came in on
     * for %ds, %es, %fs or %gs. Messing with selectors is expensive,
     * and the underlying descriptors are essentially ignored by the
     * hardware in long mode - except for the base that we override with
     * the gsbase MSRs.
     *
     * However, there's one unfortunate issue with this rosy picture --
     * a descriptor that's not marked as 'present' will still generate
     * an #np when loading a segment register.
     *
     * Consider this case.  An lwp creates a harmless LDT entry, points
     * one of it's segment registers at it, then tells the kernel (here)
     * to delete it.  In the 32-bit kernel, the #np will happen on the
     * way back to userland where we reload the segment registers, and be
     * handled in kern_gpfault().  In the 64-bit kernel, the same thing
     * will happen in the normal case too.  However, if we're trying to
     * use a debugger that wants to save and restore the segment registers,
     * and the debugger things that we have valid segment registers, we
     * have the problem that the debugger will try and restore the
     * segment register that points at the now 'not present' descriptor
     * and will take a #np right there.
     *
     * We should obviously fix the debugger to be paranoid about
     * -not- restoring segment registers that point to bad descriptors;
     * however we can prevent the problem here if we check to see if any
     * of the segment registers are still pointing at the thing we're
     * destroying; if they are, return an error instead. (That also seems
     * a lot better failure mode than SIGKILL and a core file
     * from kern_gpfault() too.)
     */
    if (SI86SSD_PRES(ssd) == 0) {
        kthread_t *t;
        int bad = 0;

        /*
         * Look carefully at the segment registers of every lwp
         * in the process (they're all stopped by our caller).
         * If we're about to invalidate a descriptor that's still
         * being referenced by *any* of them, return an error,
         * rather than having them #gp on their way out of the kernel.
         */
        ASSERT(pp->p_lwprcnt == 1);

        mutex_enter(&pp->p_lock);
        t = pp->p_tlist;
        do {
            klwp_t *lwp = ttolwp(t);
            struct regs *rp = lwp->lwp_regs;
#if defined(__amd64)
            pcb_t *pcb = &lwp->lwp_pcb;
#endif

            if (ssd->sel == rp->r_cs || ssd->sel == rp->r_ss) {
                bad = 1;
                break;
            }

#if defined(__amd64)
            if (pcb->pcb_rupdate == 1) {
                if (ssd->sel == pcb->pcb_ds ||
                    ssd->sel == pcb->pcb_es ||
                    ssd->sel == pcb->pcb_fs ||
                    ssd->sel == pcb->pcb_gs) {
                    bad = 1;
                    break;
                }
            } else
#endif
            {
                if (ssd->sel == rp->r_ds ||
                    ssd->sel == rp->r_es ||
                    ssd->sel == rp->r_fs ||
                    ssd->sel == rp->r_gs) {
                    bad = 1;
                    break;
                }
            }

        } while ((t = t->t_forw) != pp->p_tlist);
        mutex_exit(&pp->p_lock);

        if (bad) {
            mutex_exit(&pp->p_ldtlock);
            return (EBUSY);
        }
    }

    /*
     * If acc1 is zero, clear the descriptor (including the 'present' bit)
     */
    if (ssd->acc1 == 0) {
        rc  = ldt_update_segd(ldp, &null_udesc);
        mutex_exit(&pp->p_ldtlock);
        return (rc);
    }

    /*
     * Check segment type, allow segment not present and
     * only user DPL (3).
     */
    if (SI86SSD_DPL(ssd) != SEL_UPL) {
        mutex_exit(&pp->p_ldtlock);
        return (EINVAL);
    }

#if defined(__amd64)
    /*
     * Do not allow 32-bit applications to create 64-bit mode code
     * segments.
     */
    if (SI86SSD_ISUSEG(ssd) && ((SI86SSD_TYPE(ssd) >> 3) & 1) == 1 &&
        SI86SSD_ISLONG(ssd)) {
        mutex_exit(&pp->p_ldtlock);
        return (EINVAL);
    }
#endif /* __amd64 */

    /*
     * Set up a code or data user segment descriptor.
     */
    if (SI86SSD_ISUSEG(ssd)) {
        ssd_to_usd(ssd, &ndesc);
        rc = ldt_update_segd(ldp, &ndesc);
        mutex_exit(&pp->p_ldtlock);
        return (rc);
    }

#if defined(__i386)
    /*
     * Allow a call gate only if the destination is in the LDT
     * and the system is running in 32-bit legacy mode.
     *
     * In long mode 32-bit call gates are redefined as 64-bit call
     * gates and the hw enforces that the target code selector
     * of the call gate must be 64-bit selector. A #gp fault is
     * generated if otherwise. Since we do not allow 32-bit processes
     * to switch themselves to 64-bits we never allow call gates
     * on 64-bit system system.
     */
    if (SI86SSD_TYPE(ssd) == SDT_SYSCGT && SELISLDT(ssd->ls)) {


        ssd_to_sgd(ssd, (gate_desc_t *)&ndesc);
        rc = ldt_update_segd(ldp, &ndesc);
        mutex_exit(&pp->p_ldtlock);
        return (rc);
    }
#endif  /* __i386 */

    mutex_exit(&pp->p_ldtlock);
    return (EINVAL);
}

/*
 * Allocate new LDT for process just large enough to contain seli.
 * Note we allocate and grow LDT in PAGESIZE chunks. We do this
 * to simplify the implementation and because on the hypervisor it's
 * required, since the LDT must live on pages that have PROT_WRITE
 * removed and which are given to the hypervisor.
 */
static void
ldt_alloc(proc_t *pp, uint_t seli)
{
    user_desc_t *ldt;
    size_t      ldtsz;
    uint_t      nsels;

    ASSERT(MUTEX_HELD(&pp->p_ldtlock));
    ASSERT(pp->p_ldt == NULL);
    ASSERT(pp->p_ldtlimit == 0);

    /*
     * Allocate new LDT just large enough to contain seli.
     */
    ldtsz = P2ROUNDUP((seli + 1) * sizeof (user_desc_t), PAGESIZE);
    nsels = ldtsz / sizeof (user_desc_t);
    ASSERT(nsels >= MINNLDT && nsels <= MAXNLDT);

    ldt = kmem_zalloc(ldtsz, KM_SLEEP);
    ASSERT(IS_P2ALIGNED(ldt, PAGESIZE));

#if defined(__xpv)
    if (xen_ldt_setprot(ldt, ldtsz, PROT_READ))
        panic("ldt_alloc:xen_ldt_setprot(PROT_READ) failed");
#endif

    pp->p_ldt = ldt;
    pp->p_ldtlimit = nsels - 1;
    set_syssegd(&pp->p_ldt_desc, ldt, ldtsz - 1, SDT_SYSLDT, SEL_KPL);

    if (pp == curproc) {
        kpreempt_disable();
        ldt_load();
        kpreempt_enable();
    }
}

static void
ldt_free(proc_t *pp)
{
    user_desc_t *ldt;
    size_t      ldtsz;

    ASSERT(pp->p_ldt != NULL);

    mutex_enter(&pp->p_ldtlock);
    ldt = pp->p_ldt;
    ldtsz = (pp->p_ldtlimit + 1) * sizeof (user_desc_t);

    ASSERT(IS_P2ALIGNED(ldtsz, PAGESIZE));

    pp->p_ldt = NULL;
    pp->p_ldtlimit = 0;
    pp->p_ldt_desc = null_sdesc;
    mutex_exit(&pp->p_ldtlock);

    if (pp == curproc) {
        kpreempt_disable();
        ldt_unload();
        kpreempt_enable();
    }

#if defined(__xpv)
    /*
     * We are not allowed to make the ldt writable until after
     * we tell the hypervisor to unload it.
     */
    if (xen_ldt_setprot(ldt, ldtsz, PROT_READ | PROT_WRITE))
        panic("ldt_free:xen_ldt_setprot(PROT_READ|PROT_WRITE) failed");
#endif

    kmem_free(ldt, ldtsz);
}

/*
 * On fork copy new ldt for child.
 */
static void
ldt_dup(proc_t *pp, proc_t *cp)
{
    size_t  ldtsz;

    ASSERT(pp->p_ldt != NULL);
    ASSERT(cp != curproc);

    /*
     * I assume the parent's ldt can't increase since we're in a fork.
     */
    mutex_enter(&pp->p_ldtlock);
    mutex_enter(&cp->p_ldtlock);

    ldtsz = (pp->p_ldtlimit + 1) * sizeof (user_desc_t);

    ldt_alloc(cp, pp->p_ldtlimit);

#if defined(__xpv)
    /*
     * Make child's ldt writable so it can be copied into from
     * parent's ldt. This works since ldt_alloc above did not load
     * the ldt since its for the child process. If we tried to make
     * an LDT writable that is loaded in hw the setprot operation
     * would fail.
     */
    if (xen_ldt_setprot(cp->p_ldt, ldtsz, PROT_READ | PROT_WRITE))
        panic("ldt_dup:xen_ldt_setprot(PROT_READ|PROT_WRITE) failed");
#endif

    bcopy(pp->p_ldt, cp->p_ldt, ldtsz);

#if defined(__xpv)
    if (xen_ldt_setprot(cp->p_ldt, ldtsz, PROT_READ))
        panic("ldt_dup:xen_ldt_setprot(PROT_READ) failed");
#endif
    mutex_exit(&cp->p_ldtlock);
    mutex_exit(&pp->p_ldtlock);

}

static void
ldt_grow(proc_t *pp, uint_t seli)
{
    user_desc_t *oldt, *nldt;
    uint_t      nsels;
    size_t      oldtsz, nldtsz;

    ASSERT(MUTEX_HELD(&pp->p_ldtlock));
    ASSERT(pp->p_ldt != NULL);
    ASSERT(pp->p_ldtlimit != 0);

    /*
     * Allocate larger LDT just large enough to contain seli.
     */
    nldtsz = P2ROUNDUP((seli + 1) * sizeof (user_desc_t), PAGESIZE);
    nsels = nldtsz / sizeof (user_desc_t);
    ASSERT(nsels >= MINNLDT && nsels <= MAXNLDT);
    ASSERT(nsels > pp->p_ldtlimit);

    oldt = pp->p_ldt;
    oldtsz = (pp->p_ldtlimit + 1) * sizeof (user_desc_t);

    nldt = kmem_zalloc(nldtsz, KM_SLEEP);
    ASSERT(IS_P2ALIGNED(nldt, PAGESIZE));

    bcopy(oldt, nldt, oldtsz);

    /*
     * unload old ldt.
     */
    kpreempt_disable();
    ldt_unload();
    kpreempt_enable();

#if defined(__xpv)

    /*
     * Make old ldt writable and new ldt read only.
     */
    if (xen_ldt_setprot(oldt, oldtsz, PROT_READ | PROT_WRITE))
        panic("ldt_grow:xen_ldt_setprot(PROT_READ|PROT_WRITE) failed");

    if (xen_ldt_setprot(nldt, nldtsz, PROT_READ))
        panic("ldt_grow:xen_ldt_setprot(PROT_READ) failed");
#endif

    pp->p_ldt = nldt;
    pp->p_ldtlimit = nsels - 1;

    /*
     * write new ldt segment descriptor.
     */
    set_syssegd(&pp->p_ldt_desc, nldt, nldtsz - 1, SDT_SYSLDT, SEL_KPL);

    /*
     * load the new ldt.
     */
    kpreempt_disable();
    ldt_load();
    kpreempt_enable();

    kmem_free(oldt, oldtsz);
}