path: root/src/VBox/VMM/VMMAll/PDMAllCritSect.cpp

/* $Id: PDMAllCritSect.cpp $ */
/** @file
 * PDM - Write-Only Critical Section, All Contexts.
 */

/*
 * Copyright (C) 2006-2023 Oracle and/or its affiliates.
 *
 * This file is part of VirtualBox base platform packages, as
 * available from https://www.virtualbox.org.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation, in version 3 of the
 * License.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see <https://www.gnu.org/licenses>.
 *
 * SPDX-License-Identifier: GPL-3.0-only
 */


/*********************************************************************************************************************************
*   Header Files                                                                                                                 *
*********************************************************************************************************************************/
#define LOG_GROUP LOG_GROUP_PDM_CRITSECT
#include "PDMInternal.h"
#include <VBox/vmm/pdmcritsect.h>
#include <VBox/vmm/mm.h>
#include <VBox/vmm/vmm.h>
#include <VBox/vmm/vmcc.h>
#include <VBox/err.h>
#include <VBox/vmm/hm.h>

#include <VBox/log.h>
#include <iprt/asm.h>
#include <iprt/assert.h>
#ifdef IN_RING3
# include <iprt/lockvalidator.h>
#endif
#if defined(IN_RING3) || defined(IN_RING0)
# include <iprt/semaphore.h>
#endif
#ifdef IN_RING0
# include <iprt/time.h>
#endif
#if defined(IN_RING3) || defined(IN_RING0)
# include <iprt/thread.h>
#endif


/*********************************************************************************************************************************
*   Defined Constants And Macros                                                                                                 *
*********************************************************************************************************************************/
/** The number loops to spin for in ring-3. */
#define PDMCRITSECT_SPIN_COUNT_R3       20
/** The number loops to spin for in ring-0. */
#define PDMCRITSECT_SPIN_COUNT_R0       256
/** The number loops to spin for in the raw-mode context. */
#define PDMCRITSECT_SPIN_COUNT_RC       256


/** Skips some of the overly paranoid atomic updates.
 * Makes some assumptions about cache coherence, though not brave enough not to
 * always end with an atomic update. */
#define PDMCRITSECT_WITH_LESS_ATOMIC_STUFF

/* Undefine the automatic VBOX_STRICT API mappings. */
#undef PDMCritSectEnter
#undef PDMCritSectTryEnter


/**
 * Gets the ring-3 native thread handle of the calling thread.
 *
 * @returns native thread handle (ring-3).
 * @param   pVM         The cross context VM structure.
 * @param   pCritSect   The critical section. This is used in R0 and RC.
 */
DECL_FORCE_INLINE(RTNATIVETHREAD) pdmCritSectGetNativeSelf(PVMCC pVM, PCPDMCRITSECT pCritSect)
{
#ifdef IN_RING3
    RT_NOREF(pVM, pCritSect);
    RTNATIVETHREAD  hNativeSelf = RTThreadNativeSelf();

#elif defined(IN_RING0)
    AssertMsgReturn(pCritSect->s.Core.u32Magic == RTCRITSECT_MAGIC, ("%RX32\n", pCritSect->s.Core.u32Magic),
                    NIL_RTNATIVETHREAD);
    RTNATIVETHREAD  hNativeSelf = GVMMR0GetRing3ThreadForSelf(pVM);
    Assert(hNativeSelf != NIL_RTNATIVETHREAD);

#else
# error "Invalid context"
#endif
    return hNativeSelf;
}


#ifdef IN_RING0
/**
 * Marks the critical section as corrupted.
 */
DECL_NO_INLINE(static, int) pdmCritSectCorrupted(PPDMCRITSECT pCritSect, const char *pszMsg)
{
    ASMAtomicWriteU32(&pCritSect->s.Core.u32Magic, PDMCRITSECT_MAGIC_CORRUPTED);
    LogRel(("PDMCritSect: %s pCritSect=%p\n", pszMsg, pCritSect));
    return VERR_PDM_CRITSECT_IPE;
}
#endif


/**
 * Tail code called when we've won the battle for the lock.
 *
 * @returns VINF_SUCCESS.
 *
 * @param   pCritSect       The critical section.
 * @param   hNativeSelf     The native handle of this thread.
 * @param   pSrcPos         The source position of the lock operation.
 */
DECL_FORCE_INLINE(int) pdmCritSectEnterFirst(PPDMCRITSECT pCritSect, RTNATIVETHREAD hNativeSelf, PCRTLOCKVALSRCPOS pSrcPos)
{
    Assert(hNativeSelf != NIL_RTNATIVETHREAD);
    AssertMsg(pCritSect->s.Core.NativeThreadOwner == NIL_RTNATIVETHREAD, ("NativeThreadOwner=%p\n", pCritSect->s.Core.NativeThreadOwner));
    Assert(!(pCritSect->s.Core.fFlags & PDMCRITSECT_FLAGS_PENDING_UNLOCK));

# ifdef PDMCRITSECT_WITH_LESS_ATOMIC_STUFF
    pCritSect->s.Core.cNestings = 1;
# else
    ASMAtomicWriteS32(&pCritSect->s.Core.cNestings, 1);
# endif
    Assert(pCritSect->s.Core.cNestings == 1);
    ASMAtomicWriteHandle(&pCritSect->s.Core.NativeThreadOwner, hNativeSelf);

# ifdef PDMCRITSECT_STRICT
    RTLockValidatorRecExclSetOwner(pCritSect->s.Core.pValidatorRec, NIL_RTTHREAD, pSrcPos, true);
# else
    NOREF(pSrcPos);
# endif
    if (pSrcPos)
        Log12Func(("%p: uId=%p ln=%u fn=%s\n", pCritSect, pSrcPos->uId, pSrcPos->uLine, pSrcPos->pszFunction));
    else
        Log12Func(("%p\n", pCritSect));

    STAM_PROFILE_ADV_START(&pCritSect->s.StatLocked, l);
    return VINF_SUCCESS;
}


#if defined(IN_RING3) || defined(IN_RING0)
/**
 * Deals with the contended case in ring-3 and ring-0.
 *
 * @retval  VINF_SUCCESS on success.
 * @retval  VERR_SEM_DESTROYED if destroyed.
 *
 * @param   pVM         The cross context VM structure.
 * @param   pVCpu       The cross context virtual CPU structure if ring-0 and on
 *                      an EMT, otherwise NULL.
 * @param   pCritSect   The critsect.
 * @param   hNativeSelf The native thread handle.
 * @param   pSrcPos     The source position of the lock operation.
 * @param   rcBusy      The status code to return when we're in RC or R0
 */
static int pdmR3R0CritSectEnterContended(PVMCC pVM, PVMCPU pVCpu, PPDMCRITSECT pCritSect, RTNATIVETHREAD hNativeSelf,
                                         PCRTLOCKVALSRCPOS pSrcPos, int rcBusy)
{
# ifdef IN_RING0
    /*
     * If we've got queued critical section leave operations and rcBusy isn't
     * VINF_SUCCESS, return to ring-3 immediately to avoid deadlocks.
     */
    if (   !pVCpu
        || !VMCPU_FF_IS_SET(pVCpu, VMCPU_FF_PDM_CRITSECT)
        || rcBusy == VINF_SUCCESS )
    { /* likely */ }
    else
    {
        /** @todo statistics. */
        STAM_REL_COUNTER_INC(&pCritSect->s.StatContentionRZLock);
        return rcBusy;
    }
# endif

    /*
     * Start waiting.
     */
    if (ASMAtomicIncS32(&pCritSect->s.Core.cLockers) == 0)
        return pdmCritSectEnterFirst(pCritSect, hNativeSelf, pSrcPos);
# ifdef IN_RING3
    STAM_REL_COUNTER_INC(&pCritSect->s.StatContentionR3);
# else
    STAM_REL_COUNTER_INC(&pCritSect->s.StatContentionRZLock);
# endif

    /*
     * The wait loop.
     *
     * This handles VERR_TIMEOUT and VERR_INTERRUPTED.
     */
    STAM_REL_PROFILE_START(&pCritSect->s.CTX_MID_Z(StatContention,Wait), a);
    PSUPDRVSESSION const    pSession    = pVM->pSession;
    SUPSEMEVENT const       hEvent      = (SUPSEMEVENT)pCritSect->s.Core.EventSem;
# ifdef IN_RING3
#  ifdef PDMCRITSECT_STRICT
    RTTHREAD const          hThreadSelf = RTThreadSelfAutoAdopt();
    int rc2 = RTLockValidatorRecExclCheckOrder(pCritSect->s.Core.pValidatorRec, hThreadSelf, pSrcPos, RT_INDEFINITE_WAIT);
    if (RT_FAILURE(rc2))
        return rc2;
#  else
    RTTHREAD const          hThreadSelf = RTThreadSelf();
#  endif
# else /* IN_RING0 */
    uint64_t const          tsStart     = RTTimeNanoTS();
    uint64_t const          cNsMaxTotalDef = RT_NS_5MIN;
    uint64_t                cNsMaxTotal = cNsMaxTotalDef;
    uint64_t const          cNsMaxRetry = RT_NS_15SEC;
    uint32_t                cMsMaxOne   = RT_MS_5SEC;
    bool                    fNonInterruptible = false;
# endif
    for (;;)
    {
        /*
         * Do the wait.
         *
         * In ring-3 this gets cluttered by lock validation and thread state
         * maintainence.
         *
         * In ring-0 we have to deal with the possibility that the thread has
         * been signalled and the interruptible wait function returning
         * immediately.  In that case we do normal R0/RC rcBusy handling.
         *
         * We always do a timed wait here, so the event handle is revalidated
         * regularly and we won't end up stuck waiting for a destroyed critsect.
         */
        /** @todo Make SUPSemEventClose wake up all waiters. */
# ifdef IN_RING3
#  ifdef PDMCRITSECT_STRICT
        int rc9 = RTLockValidatorRecExclCheckBlocking(pCritSect->s.Core.pValidatorRec, hThreadSelf, pSrcPos,
                                                      !(pCritSect->s.Core.fFlags & RTCRITSECT_FLAGS_NO_NESTING),
                                                      RT_INDEFINITE_WAIT, RTTHREADSTATE_CRITSECT, true);
        if (RT_FAILURE(rc9))
            return rc9;
#  else
        RTThreadBlocking(hThreadSelf, RTTHREADSTATE_CRITSECT, true);
#  endif
        int const rc = SUPSemEventWaitNoResume(pSession, hEvent, RT_MS_5SEC);
        RTThreadUnblocked(hThreadSelf, RTTHREADSTATE_CRITSECT);
# else  /* IN_RING0 */
        int const rc = !fNonInterruptible
                     ? SUPSemEventWaitNoResume(pSession, hEvent, cMsMaxOne)
                     : SUPSemEventWait(pSession, hEvent, cMsMaxOne);
        Log11Func(("%p: rc=%Rrc %'RU64 ns (cMsMaxOne=%RU64 hOwner=%p)\n",
                   pCritSect, rc, RTTimeNanoTS() - tsStart, cMsMaxOne, pCritSect->s.Core.NativeThreadOwner));
# endif /* IN_RING0 */

        /*
         * Make sure the critical section hasn't been delete before continuing.
         */
        if (RT_LIKELY(pCritSect->s.Core.u32Magic == RTCRITSECT_MAGIC))
        { /* likely */ }
        else
        {
            LogRel(("PDMCritSectEnter: Destroyed while waiting; pCritSect=%p rc=%Rrc\n", pCritSect, rc));
            return VERR_SEM_DESTROYED;
        }

        /*
         * Most likely we're here because we got signalled.
         */
        if (rc == VINF_SUCCESS)
        {
            STAM_REL_PROFILE_STOP(&pCritSect->s.CTX_MID_Z(StatContention,Wait), a);
            return pdmCritSectEnterFirst(pCritSect, hNativeSelf, pSrcPos);
        }

        /*
         * Timeout and interrupted waits needs careful handling in ring-0
         * because we're cooperating with ring-3 on this critical section
         * and thus need to make absolutely sure we won't get stuck here.
         *
         * The r0 interrupted case means something is pending (termination,
         * signal, APC, debugger, whatever), so we must try our best to
         * return to the caller and to ring-3 so it can be dealt with.
         */
        if (RT_LIKELY(rc == VERR_TIMEOUT || rc == VERR_INTERRUPTED))
        {
# ifdef IN_RING0
            uint64_t const cNsElapsed = RTTimeNanoTS() - tsStart;
            int const      rcTerm     = RTThreadQueryTerminationStatus(NIL_RTTHREAD);
            AssertMsg(rcTerm == VINF_SUCCESS || rcTerm == VERR_NOT_SUPPORTED || rcTerm == VINF_THREAD_IS_TERMINATING,
                      ("rcTerm=%Rrc\n", rcTerm));
            if (rcTerm == VERR_NOT_SUPPORTED && cNsMaxTotal == cNsMaxTotalDef)
                cNsMaxTotal = RT_NS_1MIN;

            if (rc == VERR_TIMEOUT)
            {
                /* Try return get out of here with a non-VINF_SUCCESS status if
                   the thread is terminating or if the timeout has been exceeded. */
                STAM_REL_COUNTER_INC(&pVM->pdm.s.StatCritSectVerrTimeout);
                if (   rcTerm != VINF_THREAD_IS_TERMINATING
                    && cNsElapsed <= cNsMaxTotal)
                    continue;
            }
            else
            {
                /* For interrupt cases, we must return if we can.  If rcBusy is VINF_SUCCESS,
                   we will try non-interruptible sleep for a while to help resolve the issue
                   w/o guru'ing. */
                STAM_REL_COUNTER_INC(&pVM->pdm.s.StatCritSectVerrInterrupted);
                if (   rcTerm != VINF_THREAD_IS_TERMINATING
                    && rcBusy == VINF_SUCCESS
                    && pVCpu != NULL
                    && cNsElapsed <= cNsMaxTotal)
                {
                    if (!fNonInterruptible)
                    {
                        STAM_REL_COUNTER_INC(&pVM->pdm.s.StatCritSectNonInterruptibleWaits);
                        fNonInterruptible   = true;
                        cMsMaxOne           = 32;
                        uint64_t cNsLeft = cNsMaxTotal - cNsElapsed;
                        if (cNsLeft > RT_NS_10SEC)
                            cNsMaxTotal = cNsElapsed + RT_NS_10SEC;
                    }
                    continue;
                }
            }

            /*
             * Let try get out of here.  We must very carefully undo the
             * cLockers increment we did using compare-and-exchange so that
             * we don't race the semaphore signalling in PDMCritSectLeave
             * and end up with spurious wakeups and two owners at once.
             */
            uint32_t cNoIntWaits = 0;
            uint32_t cCmpXchgs   = 0;
            int32_t  cLockers    = ASMAtomicReadS32(&pCritSect->s.Core.cLockers);
            for (;;)
            {
                if (pCritSect->s.Core.u32Magic == RTCRITSECT_MAGIC)
                {
                    if (cLockers > 0 && cCmpXchgs < _64M)
                    {
                        bool fRc = ASMAtomicCmpXchgExS32(&pCritSect->s.Core.cLockers, cLockers - 1, cLockers, &cLockers);
                        if (fRc)
                        {
                            LogFunc(("Aborting wait on %p (rc=%Rrc rcTerm=%Rrc cNsElapsed=%'RU64) -> %Rrc\n", pCritSect,
                                     rc, rcTerm, cNsElapsed, rcBusy != VINF_SUCCESS ? rcBusy : rc));
                            STAM_REL_COUNTER_INC(&pVM->pdm.s.StatAbortedCritSectEnters);
                            return rcBusy != VINF_SUCCESS ? rcBusy : rc;
                        }
                        cCmpXchgs++;
                        if ((cCmpXchgs & 0xffff) == 0)
                            Log11Func(("%p: cLockers=%d cCmpXchgs=%u (hOwner=%p)\n",
                                       pCritSect, cLockers, cCmpXchgs, pCritSect->s.Core.NativeThreadOwner));
                        ASMNopPause();
                        continue;
                    }

                    if (cLockers == 0)
                    {
                        /*
                         * We are racing someone in PDMCritSectLeave.
                         *
                         * For the VERR_TIMEOUT case we'll just retry taking it the normal
                         * way for a while.  For VERR_INTERRUPTED we're in for more fun as
                         * the previous owner might not have signalled the semaphore yet,
                         * so we'll do a short non-interruptible wait instead and then guru.
                         */
                        if (   rc == VERR_TIMEOUT
                            && RTTimeNanoTS() - tsStart <= cNsMaxTotal + cNsMaxRetry)
                            break;

                        if (   rc == VERR_INTERRUPTED
                            && (   cNoIntWaits == 0
                                || RTTimeNanoTS() - (tsStart + cNsElapsed) < RT_NS_100MS))
                        {
                            int const rc2 = SUPSemEventWait(pSession, hEvent, 1 /*ms*/);
                            if (rc2 == VINF_SUCCESS)
                            {
                                STAM_REL_COUNTER_INC(&pVM->pdm.s.StatCritSectEntersWhileAborting);
                                STAM_REL_PROFILE_STOP(&pCritSect->s.CTX_MID_Z(StatContention,Wait), a);
                                return pdmCritSectEnterFirst(pCritSect, hNativeSelf, pSrcPos);
                            }
                            cNoIntWaits++;
                            cLockers = ASMAtomicReadS32(&pCritSect->s.Core.cLockers);
                            continue;
                        }
                    }
                    else
                        LogFunc(("Critical section %p has a broken cLockers count. Aborting.\n", pCritSect));

                    /* Sabotage the critical section and return error to caller. */
                    ASMAtomicWriteU32(&pCritSect->s.Core.u32Magic, PDMCRITSECT_MAGIC_FAILED_ABORT);
                    LogRel(("PDMCritSectEnter: Failed to abort wait on pCritSect=%p (rc=%Rrc rcTerm=%Rrc)\n",
                            pCritSect, rc, rcTerm));
                    return VERR_PDM_CRITSECT_ABORT_FAILED;
                }
                LogRel(("PDMCritSectEnter: Destroyed while aborting wait; pCritSect=%p/%#x rc=%Rrc rcTerm=%Rrc\n",
                        pCritSect, pCritSect->s.Core.u32Magic, rc, rcTerm));
                return VERR_SEM_DESTROYED;
            }

            /* We get here if we timed out.  Just retry now that it
               appears someone left already. */
            Assert(rc == VERR_TIMEOUT);
            cMsMaxOne = 10 /*ms*/;

# else  /* IN_RING3 */
            RT_NOREF(pVM, pVCpu, rcBusy);
# endif /* IN_RING3 */
        }
        /*
         * Any other return code is fatal.
         */
        else
        {
            AssertMsgFailed(("rc=%Rrc\n", rc));
            return RT_FAILURE_NP(rc) ? rc : -rc;
        }
    }
    /* won't get here */
}
#endif /* IN_RING3 || IN_RING0 */


/**
 * Common worker for the debug and normal APIs.
 *
 * @returns VINF_SUCCESS if entered successfully.
 * @returns rcBusy when encountering a busy critical section in RC/R0.
 * @retval  VERR_SEM_DESTROYED if the critical section is delete before or
 *          during the operation.
 *
 * @param   pVM                 The cross context VM structure.
 * @param   pCritSect           The PDM critical section to enter.
 * @param   rcBusy              The status code to return when we're in RC or R0
 * @param   pSrcPos             The source position of the lock operation.
 */
DECL_FORCE_INLINE(int) pdmCritSectEnter(PVMCC pVM, PPDMCRITSECT pCritSect, int rcBusy, PCRTLOCKVALSRCPOS pSrcPos)
{
    Assert(pCritSect->s.Core.cNestings < 8);  /* useful to catch incorrect locking */
    Assert(pCritSect->s.Core.cNestings >= 0);
#if defined(VBOX_STRICT) && defined(IN_RING0)
    /* Hope we're not messing with critical sections while in the no-block
       zone, that would complicate things a lot. */
    PVMCPUCC pVCpuAssert = VMMGetCpu(pVM);
    Assert(pVCpuAssert && VMMRZCallRing3IsEnabled(pVCpuAssert));
#endif

    /*
     * If the critical section has already been destroyed, then inform the caller.
     */
    AssertMsgReturn(pCritSect->s.Core.u32Magic == RTCRITSECT_MAGIC,
                    ("%p %RX32\n", pCritSect, pCritSect->s.Core.u32Magic),
                    VERR_SEM_DESTROYED);

    /*
     * See if we're lucky.
     */
    /* NOP ... */
    if (!(pCritSect->s.Core.fFlags & RTCRITSECT_FLAGS_NOP))
    { /* We're more likely to end up here with real critsects than a NOP one. */ }
    else
        return VINF_SUCCESS;

    RTNATIVETHREAD hNativeSelf = pdmCritSectGetNativeSelf(pVM, pCritSect);
    AssertReturn(hNativeSelf != NIL_RTNATIVETHREAD, VERR_VM_THREAD_NOT_EMT);
    /* ... not owned ... */
    if (ASMAtomicCmpXchgS32(&pCritSect->s.Core.cLockers, 0, -1))
        return pdmCritSectEnterFirst(pCritSect, hNativeSelf, pSrcPos);

    /* ... or nested. */
    if (pCritSect->s.Core.NativeThreadOwner == hNativeSelf)
    {
        Assert(pCritSect->s.Core.cNestings >= 1);
# ifdef PDMCRITSECT_WITH_LESS_ATOMIC_STUFF
        pCritSect->s.Core.cNestings += 1;
# else
        ASMAtomicIncS32(&pCritSect->s.Core.cNestings);
# endif
        ASMAtomicIncS32(&pCritSect->s.Core.cLockers);
        Log12Func(("%p: cNestings=%d cLockers=%d\n", pCritSect, pCritSect->s.Core.cNestings, pCritSect->s.Core.cLockers));
        return VINF_SUCCESS;
    }

    /*
     * Spin for a bit without incrementing the counter.
     */
    /** @todo Move this to cfgm variables since it doesn't make sense to spin on UNI
     *        cpu systems. */
    int32_t cSpinsLeft = CTX_SUFF(PDMCRITSECT_SPIN_COUNT_);
    while (cSpinsLeft-- > 0)
    {
        if (ASMAtomicCmpXchgS32(&pCritSect->s.Core.cLockers, 0, -1))
            return pdmCritSectEnterFirst(pCritSect, hNativeSelf, pSrcPos);
        ASMNopPause();
        /** @todo Should use monitor/mwait on e.g. &cLockers here, possibly with a
           cli'ed pendingpreemption check up front using sti w/ instruction fusing
           for avoiding races. Hmm ... This is assuming the other party is actually
           executing code on another CPU ... which we could keep track of if we
           wanted. */
    }

#ifdef IN_RING3
    /*
     * Take the slow path.
     */
    NOREF(rcBusy);
    return pdmR3R0CritSectEnterContended(pVM, NULL, pCritSect, hNativeSelf, pSrcPos, rcBusy);

#elif defined(IN_RING0)
# if 1 /* new code */
    /*
     * In ring-0 context we have to take the special VT-x/AMD-V HM context into
     * account when waiting on contended locks.
     *
     * While we usually (it can be VINF_SUCCESS) have the option of returning
     * rcBusy and force the caller to go back to ring-3 and to re-start the work
     * there, it's almost always more efficient to try wait for the lock here.
     * The rcBusy will be used if we encounter an VERR_INTERRUPTED situation
     * though.
     */
    PVMCPUCC pVCpu = VMMGetCpu(pVM);
    if (pVCpu)
    {
        VMMR0EMTBLOCKCTX Ctx;
        int rc = VMMR0EmtPrepareToBlock(pVCpu, rcBusy, __FUNCTION__, pCritSect, &Ctx);
        if (rc == VINF_SUCCESS)
        {
            Assert(RTThreadPreemptIsEnabled(NIL_RTTHREAD));

            rc = pdmR3R0CritSectEnterContended(pVM, pVCpu, pCritSect, hNativeSelf, pSrcPos, rcBusy);

            VMMR0EmtResumeAfterBlocking(pVCpu, &Ctx);
        }
        else
            STAM_REL_COUNTER_INC(&pCritSect->s.StatContentionRZLockBusy);
        return rc;
    }

    /* Non-EMT. */
    Assert(RTThreadPreemptIsEnabled(NIL_RTTHREAD));
    return pdmR3R0CritSectEnterContended(pVM, NULL, pCritSect, hNativeSelf, pSrcPos, rcBusy);

# else /* old code: */
    /*
     * We preemption hasn't been disabled, we can block here in ring-0.
     */
    if (   RTThreadPreemptIsEnabled(NIL_RTTHREAD)
        && ASMIntAreEnabled())
        return pdmR3R0CritSectEnterContended(pVM, VMMGetCpu(pVM), pCritSect, hNativeSelf, pSrcPos, rcBusy);

    STAM_REL_COUNTER_INC(&pCritSect->s.StatContentionRZLock);

    /*
     * Call ring-3 to acquire the critical section?
     */
    if (rcBusy == VINF_SUCCESS)
    {
        PVMCPUCC pVCpu = VMMGetCpu(pVM);
        AssertReturn(pVCpu, VERR_PDM_CRITSECT_IPE);
        return VMMRZCallRing3(pVM, pVCpu, VMMCALLRING3_PDM_CRIT_SECT_ENTER, MMHyperCCToR3(pVM, pCritSect));
    }

    /*
     * Return busy.
     */
    LogFlow(("PDMCritSectEnter: locked => R3 (%Rrc)\n", rcBusy));
    return rcBusy;
# endif  /* old code */
#else
# error "Unsupported context"
#endif
}


/**
 * Enters a PDM critical section.
 *
 * @returns VINF_SUCCESS if entered successfully.
 * @returns rcBusy when encountering a busy critical section in RC/R0.
 * @retval  VERR_SEM_DESTROYED if the critical section is delete before or
 *          during the operation.
 *
 * @param   pVM                 The cross context VM structure.
 * @param   pCritSect           The PDM critical section to enter.
 * @param   rcBusy              The status code to return when we're in RC or R0
 *                              and the section is busy.  Pass VINF_SUCCESS to
 *                              acquired the critical section thru a ring-3
 *                              call if necessary.
 *
 * @note    Even callers setting @a rcBusy to VINF_SUCCESS must either handle
 *          possible failures in ring-0 or apply
 *          PDM_CRITSECT_RELEASE_ASSERT_RC(),
 *          PDM_CRITSECT_RELEASE_ASSERT_RC_DEV(),
 *          PDM_CRITSECT_RELEASE_ASSERT_RC_DRV() or
 *          PDM_CRITSECT_RELEASE_ASSERT_RC_USB() to the return value of this
 *          function.
 */
VMMDECL(DECL_CHECK_RETURN_NOT_R3(int)) PDMCritSectEnter(PVMCC pVM, PPDMCRITSECT pCritSect, int rcBusy)
{
#ifndef PDMCRITSECT_STRICT
    return pdmCritSectEnter(pVM, pCritSect, rcBusy, NULL);
#else
    RTLOCKVALSRCPOS SrcPos = RTLOCKVALSRCPOS_INIT_NORMAL_API();
    return pdmCritSectEnter(pVM, pCritSect, rcBusy, &SrcPos);
#endif
}


/**
 * Enters a PDM critical section, with location information for debugging.
 *
 * @returns VINF_SUCCESS if entered successfully.
 * @returns rcBusy when encountering a busy critical section in RC/R0.
 * @retval  VERR_SEM_DESTROYED if the critical section is delete before or
 *          during the operation.
 *
 * @param   pVM                 The cross context VM structure.
 * @param   pCritSect           The PDM critical section to enter.
 * @param   rcBusy              The status code to return when we're in RC or R0
 *                              and the section is busy.   Pass VINF_SUCCESS to
 *                              acquired the critical section thru a ring-3
 *                              call if necessary.
 * @param   uId                 Some kind of locking location ID.  Typically a
 *                              return address up the stack.  Optional (0).
 * @param   SRC_POS             The source position where to lock is being
 *                              acquired from.  Optional.
 */
VMMDECL(DECL_CHECK_RETURN_NOT_R3(int))
PDMCritSectEnterDebug(PVMCC pVM, PPDMCRITSECT pCritSect, int rcBusy, RTHCUINTPTR uId, RT_SRC_POS_DECL)
{
#ifdef PDMCRITSECT_STRICT
    RTLOCKVALSRCPOS SrcPos = RTLOCKVALSRCPOS_INIT_DEBUG_API();
    return pdmCritSectEnter(pVM, pCritSect, rcBusy, &SrcPos);
#else
    NOREF(uId); RT_SRC_POS_NOREF();
    return pdmCritSectEnter(pVM, pCritSect, rcBusy, NULL);
#endif
}


/**
 * Common worker for the debug and normal APIs.
 *
 * @retval  VINF_SUCCESS on success.
 * @retval  VERR_SEM_BUSY if the critsect was owned.
 * @retval  VERR_SEM_NESTED if nested enter on a no nesting section. (Asserted.)
 * @retval  VERR_SEM_DESTROYED if the critical section is delete before or
 *          during the operation.
 *
 * @param   pVM         The cross context VM structure.
 * @param   pCritSect   The critical section.
 * @param   pSrcPos     The source position of the lock operation.
 */
static int pdmCritSectTryEnter(PVMCC pVM, PPDMCRITSECT pCritSect, PCRTLOCKVALSRCPOS pSrcPos)
{
    /*
     * If the critical section has already been destroyed, then inform the caller.
     */
    AssertMsgReturn(pCritSect->s.Core.u32Magic == RTCRITSECT_MAGIC,
                    ("%p %RX32\n", pCritSect, pCritSect->s.Core.u32Magic),
                    VERR_SEM_DESTROYED);

    /*
     * See if we're lucky.
     */
    /* NOP ... */
    if (!(pCritSect->s.Core.fFlags & RTCRITSECT_FLAGS_NOP))
    { /* We're more likely to end up here with real critsects than a NOP one. */ }
    else
        return VINF_SUCCESS;

    RTNATIVETHREAD hNativeSelf = pdmCritSectGetNativeSelf(pVM, pCritSect);
    AssertReturn(hNativeSelf != NIL_RTNATIVETHREAD, VERR_VM_THREAD_NOT_EMT);
    /* ... not owned ... */
    if (ASMAtomicCmpXchgS32(&pCritSect->s.Core.cLockers, 0, -1))
        return pdmCritSectEnterFirst(pCritSect, hNativeSelf, pSrcPos);

    /* ... or nested. */
    if (pCritSect->s.Core.NativeThreadOwner == hNativeSelf)
    {
        Assert(pCritSect->s.Core.cNestings >= 1);
# ifdef PDMCRITSECT_WITH_LESS_ATOMIC_STUFF
        pCritSect->s.Core.cNestings += 1;
# else
        ASMAtomicIncS32(&pCritSect->s.Core.cNestings);
# endif
        ASMAtomicIncS32(&pCritSect->s.Core.cLockers);
        Log12Func(("%p: cNestings=%d cLockers=%d\n", pCritSect, pCritSect->s.Core.cNestings, pCritSect->s.Core.cLockers));
        return VINF_SUCCESS;
    }

    /* no spinning */

    /*
     * Return busy.
     */
#ifdef IN_RING3
    STAM_REL_COUNTER_INC(&pCritSect->s.StatContentionR3);
#else
    STAM_REL_COUNTER_INC(&pCritSect->s.StatContentionRZLockBusy);
#endif
    LogFlow(("PDMCritSectTryEnter: locked\n"));
    return VERR_SEM_BUSY;
}


/**
 * Try enter a critical section.
 *
 * @retval  VINF_SUCCESS on success.
 * @retval  VERR_SEM_BUSY if the critsect was owned.
 * @retval  VERR_SEM_NESTED if nested enter on a no nesting section. (Asserted.)
 * @retval  VERR_SEM_DESTROYED if the critical section is delete before or
 *          during the operation.
 *
 * @param   pVM         The cross context VM structure.
 * @param   pCritSect   The critical section.
 */
VMMDECL(DECL_CHECK_RETURN(int)) PDMCritSectTryEnter(PVMCC pVM, PPDMCRITSECT pCritSect)
{
#ifndef PDMCRITSECT_STRICT
    return pdmCritSectTryEnter(pVM, pCritSect, NULL);
#else
    RTLOCKVALSRCPOS SrcPos = RTLOCKVALSRCPOS_INIT_NORMAL_API();
    return pdmCritSectTryEnter(pVM, pCritSect, &SrcPos);
#endif
}


/**
 * Try enter a critical section, with location information for debugging.
 *
 * @retval  VINF_SUCCESS on success.
 * @retval  VERR_SEM_BUSY if the critsect was owned.
 * @retval  VERR_SEM_NESTED if nested enter on a no nesting section. (Asserted.)
 * @retval  VERR_SEM_DESTROYED if the critical section is delete before or
 *          during the operation.
 *
 * @param   pVM                 The cross context VM structure.
 * @param   pCritSect           The critical section.
 * @param   uId                 Some kind of locking location ID.  Typically a
 *                              return address up the stack.  Optional (0).
 * @param   SRC_POS             The source position where to lock is being
 *                              acquired from.  Optional.
 */
VMMDECL(DECL_CHECK_RETURN(int))
PDMCritSectTryEnterDebug(PVMCC pVM, PPDMCRITSECT pCritSect, RTHCUINTPTR uId, RT_SRC_POS_DECL)
{
#ifdef PDMCRITSECT_STRICT
    RTLOCKVALSRCPOS SrcPos = RTLOCKVALSRCPOS_INIT_DEBUG_API();
    return pdmCritSectTryEnter(pVM, pCritSect, &SrcPos);
#else
    NOREF(uId); RT_SRC_POS_NOREF();
    return pdmCritSectTryEnter(pVM, pCritSect, NULL);
#endif
}


#ifdef IN_RING3
/**
 * Enters a PDM critical section.
 *
 * @returns VINF_SUCCESS if entered successfully.
 * @returns rcBusy when encountering a busy critical section in GC/R0.
 * @retval  VERR_SEM_DESTROYED if the critical section is delete before or
 *          during the operation.
 *
 * @param   pVM                 The cross context VM structure.
 * @param   pCritSect           The PDM critical section to enter.
 * @param   fCallRing3          Whether this is a VMMRZCallRing3()request.
 */
VMMR3DECL(int) PDMR3CritSectEnterEx(PVM pVM, PPDMCRITSECT pCritSect, bool fCallRing3)
{
    int rc = PDMCritSectEnter(pVM, pCritSect, VERR_IGNORED);
    if (    rc == VINF_SUCCESS
        &&  fCallRing3
        &&  pCritSect->s.Core.pValidatorRec
        &&  pCritSect->s.Core.pValidatorRec->hThread != NIL_RTTHREAD)
        RTLockValidatorRecExclReleaseOwnerUnchecked(pCritSect->s.Core.pValidatorRec);
    return rc;
}
#endif /* IN_RING3 */


/**
 * Leaves a critical section entered with PDMCritSectEnter().
 *
 * @returns Indication whether we really exited the critical section.
 * @retval  VINF_SUCCESS if we really exited.
 * @retval  VINF_SEM_NESTED if we only reduced the nesting count.
 * @retval  VERR_NOT_OWNER if you somehow ignore release assertions.
 *
 * @param   pVM         The cross context VM structure.
 * @param   pCritSect   The PDM critical section to leave.
 *
 * @remarks Can be called from no-ring-3-call context in ring-0 (TM/VirtualSync)
 *          where we'll queue leaving operation for ring-3 processing.
 */
VMMDECL(int) PDMCritSectLeave(PVMCC pVM, PPDMCRITSECT pCritSect)
{
    AssertMsg(pCritSect->s.Core.u32Magic == RTCRITSECT_MAGIC, ("%p %RX32\n", pCritSect, pCritSect->s.Core.u32Magic));
    Assert(pCritSect->s.Core.u32Magic == RTCRITSECT_MAGIC);

    /*
     * Check for NOP sections before asserting ownership.
     */
    if (!(pCritSect->s.Core.fFlags & RTCRITSECT_FLAGS_NOP))
    { /* We're more likely to end up here with real critsects than a NOP one. */ }
    else
        return VINF_SUCCESS;

    /*
     * Always check that the caller is the owner (screw performance).
     */
    RTNATIVETHREAD const hNativeSelf = pdmCritSectGetNativeSelf(pVM, pCritSect);
    VMM_ASSERT_RELEASE_MSG_RETURN(pVM, pCritSect->s.Core.NativeThreadOwner == hNativeSelf && hNativeSelf != NIL_RTNATIVETHREAD,
                                  ("%p %s: %p != %p; cLockers=%d cNestings=%d\n", pCritSect, R3STRING(pCritSect->s.pszName),
                                   pCritSect->s.Core.NativeThreadOwner, hNativeSelf,
                                   pCritSect->s.Core.cLockers, pCritSect->s.Core.cNestings),
                                  VERR_NOT_OWNER);

    /*
     * Nested leave.
     */
    int32_t const cNestings = pCritSect->s.Core.cNestings;
    Assert(cNestings >= 1);
    if (cNestings > 1)
    {
#ifdef PDMCRITSECT_WITH_LESS_ATOMIC_STUFF
        pCritSect->s.Core.cNestings = cNestings - 1;
#else
        ASMAtomicWriteS32(&pCritSect->s.Core.cNestings, cNestings - 1);
#endif
        int32_t const cLockers = ASMAtomicDecS32(&pCritSect->s.Core.cLockers);
        Assert(cLockers >= 0); RT_NOREF(cLockers);
        Log12Func(("%p: cNestings=%d cLockers=%d\n", pCritSect, cNestings - 1, cLockers));
        return VINF_SEM_NESTED;
    }

    Log12Func(("%p: cNestings=%d cLockers=%d hOwner=%p - leave for real\n",
               pCritSect, cNestings, pCritSect->s.Core.cLockers, pCritSect->s.Core.NativeThreadOwner));

#ifdef IN_RING3
    /*
     * Ring-3: Leave for real.
     */
    SUPSEMEVENT const hEventToSignal = pCritSect->s.hEventToSignal;
    pCritSect->s.hEventToSignal = NIL_SUPSEMEVENT;

# if defined(PDMCRITSECT_STRICT)
    if (pCritSect->s.Core.pValidatorRec->hThread != NIL_RTTHREAD)
        RTLockValidatorRecExclReleaseOwnerUnchecked(pCritSect->s.Core.pValidatorRec);
# endif
    Assert(!pCritSect->s.Core.pValidatorRec || pCritSect->s.Core.pValidatorRec->hThread == NIL_RTTHREAD);

# ifdef PDMCRITSECT_WITH_LESS_ATOMIC_STUFF
    //pCritSect->s.Core.cNestings = 0; /* not really needed */
    pCritSect->s.Core.NativeThreadOwner = NIL_RTNATIVETHREAD;
# else
    ASMAtomicWriteS32(&pCritSect->s.Core.cNestings, 0);
    ASMAtomicWriteHandle(&pCritSect->s.Core.NativeThreadOwner, NIL_RTNATIVETHREAD);
# endif
    ASMAtomicAndU32(&pCritSect->s.Core.fFlags, ~PDMCRITSECT_FLAGS_PENDING_UNLOCK);

    /* Stop profiling and decrement lockers. */
    STAM_PROFILE_ADV_STOP(&pCritSect->s.StatLocked, l);
    ASMCompilerBarrier();
    int32_t const cLockers = ASMAtomicDecS32(&pCritSect->s.Core.cLockers);
    if (cLockers < 0)
        AssertMsg(cLockers == -1, ("cLockers=%d\n", cLockers));
    else
    {
        /* Someone is waiting, wake up one of them. */
        Assert(cLockers < _8K);
        Log8(("PDMCritSectLeave: Waking up %p (cLockers=%u)\n", pCritSect, cLockers));
        SUPSEMEVENT hEvent = (SUPSEMEVENT)pCritSect->s.Core.EventSem;
        int rc = SUPSemEventSignal(pVM->pSession, hEvent);
        AssertRC(rc);
    }

    /* Signal exit event. */
    if (RT_LIKELY(hEventToSignal == NIL_SUPSEMEVENT))
    { /* likely */ }
    else
    {
        Log8(("PDMCritSectLeave: Signalling %#p (%p)\n", hEventToSignal, pCritSect));
        int rc = SUPSemEventSignal(pVM->pSession, hEventToSignal);
        AssertRC(rc);
    }

    return VINF_SUCCESS;


#elif defined(IN_RING0)
    /*
     * Ring-0: Try leave for real, depends on host and context.
     */
    SUPSEMEVENT const hEventToSignal = pCritSect->s.hEventToSignal;
    pCritSect->s.hEventToSignal = NIL_SUPSEMEVENT;
    PVMCPUCC pVCpu           = VMMGetCpu(pVM);
    bool     fQueueOnTrouble = false; /* Set this to true to test queueing. */
    if (   pVCpu == NULL /* non-EMT access, if we implement it must be able to block */
        || VMMRZCallRing3IsEnabled(pVCpu)
        || RTSemEventIsSignalSafe()
        || (   VMMR0ThreadCtxHookIsEnabled(pVCpu)       /* Doesn't matter if Signal() blocks if we have hooks, ... */
            && RTThreadPreemptIsEnabled(NIL_RTTHREAD)   /* ... and preemption is still enabled, */
            && ASMIntAreEnabled())                      /* ... and interrupts hasn't yet been disabled. Special pre-GC HM env. */
        || (fQueueOnTrouble = (   hEventToSignal == NIL_SUPSEMEVENT
                               && ASMAtomicUoReadS32(&pCritSect->s.Core.cLockers) == 0)) )
    {
        pCritSect->s.hEventToSignal = NIL_SUPSEMEVENT;

# ifdef PDMCRITSECT_WITH_LESS_ATOMIC_STUFF
        //pCritSect->s.Core.cNestings = 0; /* not really needed */
        pCritSect->s.Core.NativeThreadOwner = NIL_RTNATIVETHREAD;
# else
        ASMAtomicWriteS32(&pCritSect->s.Core.cNestings, 0);
        ASMAtomicWriteHandle(&pCritSect->s.Core.NativeThreadOwner, NIL_RTNATIVETHREAD);
# endif
        ASMAtomicAndU32(&pCritSect->s.Core.fFlags, ~PDMCRITSECT_FLAGS_PENDING_UNLOCK);

        /*
         * Stop profiling and decrement lockers.
         */
        STAM_PROFILE_ADV_STOP(&pCritSect->s.StatLocked, l);
        ASMCompilerBarrier();

        bool    fQueueIt = false;
        int32_t cLockers;
        if (!fQueueOnTrouble)
            cLockers = ASMAtomicDecS32(&pCritSect->s.Core.cLockers);
        else
        {
            cLockers = -1;
            if (!ASMAtomicCmpXchgS32(&pCritSect->s.Core.cLockers, -1, 0))
                fQueueIt = true;
        }
        if (!fQueueIt)
        {
            VMMR0EMTBLOCKCTX    Ctx;
            bool                fLeaveCtx = false;
            if (cLockers < 0)
                AssertMsg(cLockers == -1, ("cLockers=%d\n", cLockers));
            else
            {
                /* Someone is waiting, wake up one of them. */
                Assert(cLockers < _8K);
                SUPSEMEVENT hEvent = (SUPSEMEVENT)pCritSect->s.Core.EventSem;
                if (!RTSemEventIsSignalSafe() && (pVCpu = VMMGetCpu(pVM)) != NULL)
                {
                    int rc = VMMR0EmtPrepareToBlock(pVCpu, VINF_SUCCESS, __FUNCTION__, pCritSect, &Ctx);
                    VMM_ASSERT_RELEASE_MSG_RETURN(pVM, RT_SUCCESS(rc), ("rc=%Rrc\n", rc), rc);
                    fLeaveCtx = true;
                }
                int rc = SUPSemEventSignal(pVM->pSession, hEvent);
                AssertRC(rc);
            }

            /*
             * Signal exit event.
             */
            if (RT_LIKELY(hEventToSignal == NIL_SUPSEMEVENT))
            { /* likely */ }
            else
            {
                if (!fLeaveCtx && pVCpu != NULL && !RTSemEventIsSignalSafe() && (pVCpu = VMMGetCpu(pVM)) != NULL)
                {
                    int rc = VMMR0EmtPrepareToBlock(pVCpu, VINF_SUCCESS, __FUNCTION__, pCritSect, &Ctx);
                    VMM_ASSERT_RELEASE_MSG_RETURN(pVM, RT_SUCCESS(rc), ("rc=%Rrc\n", rc), rc);
                    fLeaveCtx = true;
                }
                Log8(("Signalling %#p\n", hEventToSignal));
                int rc = SUPSemEventSignal(pVM->pSession, hEventToSignal);
                AssertRC(rc);
            }

            /*
             * Restore HM context if needed.
             */
            if (!fLeaveCtx)
            { /* contention should be unlikely */ }
            else
                VMMR0EmtResumeAfterBlocking(pVCpu, &Ctx);

# ifdef DEBUG_bird
            VMMTrashVolatileXMMRegs();
# endif
            return VINF_SUCCESS;
        }

        /*
         * Darn, someone raced in on us.  Restore the state (this works only
         * because the semaphore is effectively controlling ownership).
         */
        bool fRc;
        RTNATIVETHREAD hMessOwner = NIL_RTNATIVETHREAD;
        ASMAtomicCmpXchgExHandle(&pCritSect->s.Core.NativeThreadOwner, hNativeSelf, NIL_RTNATIVETHREAD, fRc, &hMessOwner);
        AssertLogRelMsgReturn(fRc, ("pCritSect=%p hMessOwner=%p\n", pCritSect, hMessOwner),
                              pdmCritSectCorrupted(pCritSect, "owner race"));
        STAM_PROFILE_ADV_START(&pCritSect->s.StatLocked, l);
# ifdef PDMCRITSECT_WITH_LESS_ATOMIC_STUFF
        //pCritSect->s.Core.cNestings = 1;
        Assert(pCritSect->s.Core.cNestings == 1);
# else
        //Assert(pCritSect->s.Core.cNestings == 0);
        ASMAtomicWriteS32(&pCritSect->s.Core.cNestings, 1);
# endif
        Assert(hEventToSignal == NIL_SUPSEMEVENT);
    }


#else /* IN_RC */
    /*
     * Raw-mode: Try leave it.
     */
# error "This context is not use..."
    if (pCritSect->s.Core.cLockers == 0)
    {
# ifdef PDMCRITSECT_WITH_LESS_ATOMIC_STUFF
        //pCritSect->s.Core.cNestings = 0; /* not really needed */
# else
        ASMAtomicWriteS32(&pCritSect->s.Core.cNestings, 0);
# endif
        ASMAtomicAndU32(&pCritSect->s.Core.fFlags, ~PDMCRITSECT_FLAGS_PENDING_UNLOCK);
        STAM_PROFILE_ADV_STOP(&pCritSect->s.StatLocked, l);

        ASMAtomicWriteHandle(&pCritSect->s.Core.NativeThreadOwner, NIL_RTNATIVETHREAD);
        if (ASMAtomicCmpXchgS32(&pCritSect->s.Core.cLockers, -1, 0))
            return VINF_SUCCESS;

        /*
         * Darn, someone raced in on us.  Restore the state (this works only
         * because the semaphore is effectively controlling ownership).
         */
        bool fRc;
        RTNATIVETHREAD hMessOwner = NIL_RTNATIVETHREAD;
        ASMAtomicCmpXchgExHandle(&pCritSect->s.Core.NativeThreadOwner, hNativeSelf, NIL_RTNATIVETHREAD, fRc, &hMessOwner);
        AssertLogRelMsgReturn(fRc, ("pCritSect=%p hMessOwner=%p\n", pCritSect, hMessOwner),
                              pdmCritSectCorrupted(pCritSect, "owner race"));
        STAM_PROFILE_ADV_START(&pCritSect->s.StatLocked, l);
# ifdef PDMCRITSECT_WITH_LESS_ATOMIC_STUFF
        //pCritSect->s.Core.cNestings = 1;
        Assert(pCritSect->s.Core.cNestings == 1);
# else
        //Assert(pCritSect->s.Core.cNestings == 0);
        ASMAtomicWriteS32(&pCritSect->s.Core.cNestings, 1);
# endif
    }
#endif /* IN_RC */


#ifndef IN_RING3
    /*
     * Ring-0/raw-mode: Unable to leave. Queue the leave for ring-3.
     */
    ASMAtomicOrU32(&pCritSect->s.Core.fFlags, PDMCRITSECT_FLAGS_PENDING_UNLOCK);
# ifndef IN_RING0
    PVMCPUCC    pVCpu = VMMGetCpu(pVM);
# endif
    uint32_t    i     = pVCpu->pdm.s.cQueuedCritSectLeaves++;
    LogFlow(("PDMCritSectLeave: [%d]=%p => R3\n", i, pCritSect));
    VMM_ASSERT_RELEASE_MSG_RETURN(pVM, i < RT_ELEMENTS(pVCpu->pdm.s.apQueuedCritSectLeaves), ("%d\n", i), VERR_PDM_CRITSECT_IPE);
    pVCpu->pdm.s.apQueuedCritSectLeaves[i] = pCritSect->s.pSelfR3;
    VMM_ASSERT_RELEASE_MSG_RETURN(pVM,
                                     RT_VALID_PTR(pVCpu->pdm.s.apQueuedCritSectLeaves[i])
                                  &&    ((uintptr_t)pVCpu->pdm.s.apQueuedCritSectLeaves[i] & HOST_PAGE_OFFSET_MASK)
                                     == ((uintptr_t)pCritSect & HOST_PAGE_OFFSET_MASK),
                                  ("%p vs %p\n", pVCpu->pdm.s.apQueuedCritSectLeaves[i], pCritSect),
                                  pdmCritSectCorrupted(pCritSect, "Invalid pSelfR3 value"));
    VMCPU_FF_SET(pVCpu, VMCPU_FF_PDM_CRITSECT); /** @todo handle VMCPU_FF_PDM_CRITSECT in ring-0 outside the no-call-ring-3 part. */
    VMCPU_FF_SET(pVCpu, VMCPU_FF_TO_R3); /* unnecessary paranoia */
    STAM_REL_COUNTER_INC(&pVM->pdm.s.StatQueuedCritSectLeaves);
    STAM_REL_COUNTER_INC(&pCritSect->s.StatContentionRZUnlock);

    return VINF_SUCCESS;
#endif /* IN_RING3 */
}


#if defined(IN_RING0) || defined(IN_RING3)
/**
 * Schedule a event semaphore for signalling upon critsect exit.
 *
 * @returns VINF_SUCCESS on success.
 * @returns VERR_TOO_MANY_SEMAPHORES if an event was already scheduled.
 * @returns VERR_NOT_OWNER if we're not the critsect owner (ring-3 only).
 * @returns VERR_SEM_DESTROYED if RTCritSectDelete was called while waiting.
 *
 * @param   pCritSect       The critical section.
 * @param   hEventToSignal  The support driver event semaphore that should be
 *                          signalled.
 */
VMMDECL(int) PDMHCCritSectScheduleExitEvent(PPDMCRITSECT pCritSect, SUPSEMEVENT hEventToSignal)
{
    AssertPtr(pCritSect);
    Assert(!(pCritSect->s.Core.fFlags & RTCRITSECT_FLAGS_NOP));
    Assert(hEventToSignal != NIL_SUPSEMEVENT);
# ifdef IN_RING3
    if (RT_UNLIKELY(!RTCritSectIsOwner(&pCritSect->s.Core)))
        return VERR_NOT_OWNER;
# endif
    if (RT_LIKELY(   pCritSect->s.hEventToSignal == NIL_RTSEMEVENT
                  || pCritSect->s.hEventToSignal == hEventToSignal))
    {
        pCritSect->s.hEventToSignal = hEventToSignal;
        return VINF_SUCCESS;
    }
    return VERR_TOO_MANY_SEMAPHORES;
}
#endif /* IN_RING0 || IN_RING3 */


/**
 * Checks the caller is the owner of the critical section.
 *
 * @returns true if owner.
 * @returns false if not owner.
 * @param   pVM         The cross context VM structure.
 * @param   pCritSect   The critical section.
 */
VMMDECL(bool) PDMCritSectIsOwner(PVMCC pVM, PCPDMCRITSECT pCritSect)
{
#ifdef IN_RING3
    RT_NOREF(pVM);
    return RTCritSectIsOwner(&pCritSect->s.Core);
#else
    PVMCPUCC pVCpu = VMMGetCpu(pVM);
    if (   !pVCpu
        || pCritSect->s.Core.NativeThreadOwner != pVCpu->hNativeThread)
        return false;
    return (pCritSect->s.Core.fFlags & PDMCRITSECT_FLAGS_PENDING_UNLOCK) == 0
        || pCritSect->s.Core.cNestings > 1;
#endif
}


/**
 * Checks the specified VCPU is the owner of the critical section.
 *
 * @returns true if owner.
 * @returns false if not owner.
 * @param   pVCpu       The cross context virtual CPU structure.
 * @param   pCritSect   The critical section.
 */
VMMDECL(bool) PDMCritSectIsOwnerEx(PVMCPUCC pVCpu, PCPDMCRITSECT pCritSect)
{
#ifdef IN_RING3
    NOREF(pVCpu);
    return RTCritSectIsOwner(&pCritSect->s.Core);
#else
    Assert(VMCC_GET_CPU(pVCpu->CTX_SUFF(pVM), pVCpu->idCpu) == pVCpu);
    if (pCritSect->s.Core.NativeThreadOwner != pVCpu->hNativeThread)
        return false;
    return (pCritSect->s.Core.fFlags & PDMCRITSECT_FLAGS_PENDING_UNLOCK) == 0
        || pCritSect->s.Core.cNestings > 1;
#endif
}


/**
 * Checks if anyone is waiting on the critical section we own.
 *
 * @returns true if someone is waiting.
 * @returns false if no one is waiting.
 * @param   pVM         The cross context VM structure.
 * @param   pCritSect   The critical section.
 */
VMMDECL(bool) PDMCritSectHasWaiters(PVMCC pVM, PCPDMCRITSECT pCritSect)
{
    AssertReturn(pCritSect->s.Core.u32Magic == RTCRITSECT_MAGIC, false);
    Assert(pCritSect->s.Core.NativeThreadOwner == pdmCritSectGetNativeSelf(pVM, pCritSect)); RT_NOREF(pVM);
    return pCritSect->s.Core.cLockers >= pCritSect->s.Core.cNestings;
}


/**
 * Checks if a critical section is initialized or not.
 *
 * @returns true if initialized.
 * @returns false if not initialized.
 * @param   pCritSect   The critical section.
 */
VMMDECL(bool) PDMCritSectIsInitialized(PCPDMCRITSECT pCritSect)
{
    return RTCritSectIsInitialized(&pCritSect->s.Core);
}


/**
 * Gets the recursion depth.
 *
 * @returns The recursion depth.
 * @param   pCritSect   The critical section.
 */
VMMDECL(uint32_t) PDMCritSectGetRecursion(PCPDMCRITSECT pCritSect)
{
    return RTCritSectGetRecursion(&pCritSect->s.Core);
}