ke/i386/kiinit.c

/*
 * PROJECT:         ReactOS Kernel
 * LICENSE:         GPL - See COPYING in the top level directory
 * FILE:            ntoskrnl/ke/i386/kiinit.c
 * PURPOSE:         Kernel Initialization for x86 CPUs
 * PROGRAMMERS:     Alex Ionescu (alex.ionescu@reactos.org)
 */

/* INCLUDES *****************************************************************/

#include <ntoskrnl.h>
#define NDEBUG
#include <debug.h>
#include "internal/i386/trap_x.h"

/* GLOBALS *******************************************************************/

/* Boot and double-fault/NMI/DPC stack */
UCHAR DECLSPEC_ALIGN(PAGE_SIZE) P0BootStackData[KERNEL_STACK_SIZE] = {0};
UCHAR DECLSPEC_ALIGN(PAGE_SIZE) KiDoubleFaultStackData[KERNEL_STACK_SIZE] = {0};
ULONG_PTR P0BootStack = (ULONG_PTR)&P0BootStackData[KERNEL_STACK_SIZE];
ULONG_PTR KiDoubleFaultStack = (ULONG_PTR)&KiDoubleFaultStackData[KERNEL_STACK_SIZE];

/* Spinlocks used only on X86 */
KSPIN_LOCK KiFreezeExecutionLock;
KSPIN_LOCK Ki486CompatibilityLock;

/* Perf */
ULONG ProcessCount;
ULONGLONG BootCycles, BootCyclesEnd;

/* FUNCTIONS *****************************************************************/

CODE_SEG("INIT")
VOID
NTAPI
KiInitMachineDependent(VOID)
{
    ULONG CpuCount;
    BOOLEAN FbCaching = FALSE;
    NTSTATUS Status;
    ULONG ReturnLength;
    ULONG i, Affinity, Sample = 0;
    PFX_SAVE_AREA FxSaveArea;
    ULONG MXCsrMask = 0xFFBF;
    CPU_INFO CpuInfo;
    KI_SAMPLE_MAP Samples[10];
    PKI_SAMPLE_MAP CurrentSample = Samples;
    LARGE_IDENTITY_MAP IdentityMap;

    /* Check for large page support */
    if (KeFeatureBits & KF_LARGE_PAGE)
    {
        /* Do an IPI to enable it on all CPUs */
        if (Ki386CreateIdentityMap(&IdentityMap, Ki386EnableCurrentLargePage, 2))
            KeIpiGenericCall(Ki386EnableTargetLargePage, (ULONG_PTR)&IdentityMap);

        /* Free the pages allocated for identity map */
        Ki386FreeIdentityMap(&IdentityMap);
    }

    /* Check for global page support */
    if (KeFeatureBits & KF_GLOBAL_PAGE)
    {
        /* Do an IPI to enable it on all CPUs */
        CpuCount = KeNumberProcessors;
        KeIpiGenericCall(Ki386EnableGlobalPage, (ULONG_PTR)&CpuCount);
    }

    /* Check for PAT and/or MTRR support */
    if (KeFeatureBits & (KF_PAT | KF_MTRR))
    {
        /* Query the HAL to make sure we can use it */
        Status = HalQuerySystemInformation(HalFrameBufferCachingInformation,
                                           sizeof(BOOLEAN),
                                           &FbCaching,
                                           &ReturnLength);
        if ((NT_SUCCESS(Status)) && (FbCaching))
        {
            /* We can't, disable it */
            KeFeatureBits &= ~(KF_PAT | KF_MTRR);
        }
    }

    /* Check for PAT support and enable it */
    if (KeFeatureBits & KF_PAT) KiInitializePAT();

    /* Check for CR4 support */
    if (KeFeatureBits & KF_CR4)
    {
        /* Do an IPI call to enable the Debug Exceptions */
        CpuCount = KeNumberProcessors;
        KeIpiGenericCall(Ki386EnableDE, (ULONG_PTR)&CpuCount);
    }

    /* Check if FXSR was found */
    if (KeFeatureBits & KF_FXSR)
    {
        /* Do an IPI call to enable the FXSR */
        CpuCount = KeNumberProcessors;
        KeIpiGenericCall(Ki386EnableFxsr, (ULONG_PTR)&CpuCount);

        /* Check if XMM was found too */
        if (KeFeatureBits & KF_XMMI)
        {
            /* Do an IPI call to enable XMMI exceptions */
            CpuCount = KeNumberProcessors;
            KeIpiGenericCall(Ki386EnableXMMIExceptions, (ULONG_PTR)&CpuCount);

            /* FIXME: Implement and enable XMM Page Zeroing for Mm */

            /* Patch the RtlPrefetchMemoryNonTemporal routine to enable it */
            *(PCHAR)RtlPrefetchMemoryNonTemporal = 0x90; // NOP
        }
    }

    /* Check for, and enable SYSENTER support */
    KiRestoreFastSyscallReturnState();

    /* Loop every CPU */
    i = KeActiveProcessors;
    for (Affinity = 1; i; Affinity <<= 1)
    {
        /* Check if this is part of the set */
        if (i & Affinity)
        {
            /* Run on this CPU */
            i &= ~Affinity;
            KeSetSystemAffinityThread(Affinity);

            /* Reset MHz to 0 for this CPU */
            KeGetCurrentPrcb()->MHz = 0;

            /* Check if we can use RDTSC */
            if (KeFeatureBits & KF_RDTSC)
            {
                /* Start sampling loop */
                for (;;)
                {
                    /* Do a dummy CPUID to start the sample */
                    KiCpuId(&CpuInfo, 0);

                    /* Fill out the starting data */
                    CurrentSample->PerfStart = KeQueryPerformanceCounter(NULL);
                    CurrentSample->TSCStart = __rdtsc();
                    CurrentSample->PerfFreq.QuadPart = -50000;

                    /* Sleep for this sample */
                    KeDelayExecutionThread(KernelMode,
                                           FALSE,
                                           &CurrentSample->PerfFreq);

                    /* Do another dummy CPUID */
                    KiCpuId(&CpuInfo, 0);

                    /* Fill out the ending data */
                    CurrentSample->PerfEnd =
                        KeQueryPerformanceCounter(&CurrentSample->PerfFreq);
                    CurrentSample->TSCEnd = __rdtsc();

                    /* Calculate the differences */
                    CurrentSample->PerfDelta = CurrentSample->PerfEnd.QuadPart -
                                               CurrentSample->PerfStart.QuadPart;
                    CurrentSample->TSCDelta = CurrentSample->TSCEnd -
                                              CurrentSample->TSCStart;

                    /* Compute CPU Speed */
                    CurrentSample->MHz = (ULONG)((CurrentSample->TSCDelta *
                                                  CurrentSample->
                                                  PerfFreq.QuadPart + 500000) /
                                                 (CurrentSample->PerfDelta *
                                                  1000000));

                    /* Check if this isn't the first sample */
                    if (Sample)
                    {
                        /* Check if we got a good precision within 1MHz */
                        if ((CurrentSample->MHz == CurrentSample[-1].MHz) ||
                            (CurrentSample->MHz == CurrentSample[-1].MHz + 1) ||
                            (CurrentSample->MHz == CurrentSample[-1].MHz - 1))
                        {
                            /* We did, stop sampling */
                            break;
                        }
                    }

                    /* Move on */
                    CurrentSample++;
                    Sample++;

                    if (Sample == RTL_NUMBER_OF(Samples))
                    {
                        /* No luck. Average the samples and be done */
                        ULONG TotalMHz = 0;
                        while (Sample--)
                        {
                            TotalMHz += Samples[Sample].MHz;
                        }
                        CurrentSample[-1].MHz = TotalMHz / RTL_NUMBER_OF(Samples);
                        DPRINT1("Sampling CPU frequency failed. Using average of %lu MHz\n", CurrentSample[-1].MHz);
                        break;
                    }
                }

                /* Save the CPU Speed */
                KeGetCurrentPrcb()->MHz = CurrentSample[-1].MHz;
            }

            /* Check if we have MTRR */
            if (KeFeatureBits & KF_MTRR)
            {
                /* Then manually initialize MTRR for the CPU */
                KiInitializeMTRR(i ? FALSE : TRUE);
            }

            /* Check if we have AMD MTRR and initialize it for the CPU */
            if (KeFeatureBits & KF_AMDK6MTRR) KiAmdK6InitializeMTRR();

            /* Check if this is a buggy Pentium and apply the fixup if so */
            if (KiI386PentiumLockErrataPresent) KiI386PentiumLockErrataFixup();

            /* Check if the CPU supports FXSR */
            if (KeFeatureBits & KF_FXSR)
            {
                /* Get the current thread NPX state */
                FxSaveArea = KiGetThreadNpxArea(KeGetCurrentThread());

                /* Clear initial MXCsr mask */
                FxSaveArea->U.FxArea.MXCsrMask = 0;

                /* Save the current NPX State */
                Ke386SaveFpuState(FxSaveArea);

                /* Check if the current mask doesn't match the reserved bits */
                if (FxSaveArea->U.FxArea.MXCsrMask != 0)
                {
                    /* Then use whatever it's holding */
                    MXCsrMask = FxSaveArea->U.FxArea.MXCsrMask;
                }

                /* Check if nobody set the kernel-wide mask */
                if (!KiMXCsrMask)
                {
                    /* Then use the one we calculated above */
                    KiMXCsrMask = MXCsrMask;
                }
                else
                {
                    /* Was it set to the same value we found now? */
                    if (KiMXCsrMask != MXCsrMask)
                    {
                        /* No, something is definitely wrong */
                        KeBugCheckEx(MULTIPROCESSOR_CONFIGURATION_NOT_SUPPORTED,
                                     KF_FXSR,
                                     KiMXCsrMask,
                                     MXCsrMask,
                                     0);
                    }
                }

                /* Now set the kernel mask */
                KiMXCsrMask &= MXCsrMask;
            }
        }
    }

    /* Return affinity back to where it was */
    KeRevertToUserAffinityThread();

    /* NT allows limiting the duration of an ISR with a registry key */
    if (KiTimeLimitIsrMicroseconds)
    {
        /* FIXME: TODO */
        DPRINT1("ISR Time Limit not yet supported\n");
    }

    /* Set CR0 features based on detected CPU */
    KiSetCR0Bits();
}

CODE_SEG("INIT")
VOID
NTAPI
KiInitializePcr(IN ULONG ProcessorNumber,
                IN PKIPCR Pcr,
                IN PKIDTENTRY Idt,
                IN PKGDTENTRY Gdt,
                IN PKTSS Tss,
                IN PKTHREAD IdleThread,
                IN PVOID DpcStack)
{
    /* Setup the TIB */
    Pcr->NtTib.ExceptionList = EXCEPTION_CHAIN_END;
    Pcr->NtTib.StackBase = 0;
    Pcr->NtTib.StackLimit = 0;
    Pcr->NtTib.Self = NULL;

    /* Set the Current Thread */
    Pcr->PrcbData.CurrentThread = IdleThread;

    /* Set pointers to ourselves */
    Pcr->SelfPcr = (PKPCR)Pcr;
    Pcr->Prcb = &Pcr->PrcbData;

    /* Set the PCR Version */
    Pcr->MajorVersion = PCR_MAJOR_VERSION;
    Pcr->MinorVersion = PCR_MINOR_VERSION;

    /* Set the PCRB Version */
    Pcr->PrcbData.MajorVersion = PRCB_MAJOR_VERSION;
    Pcr->PrcbData.MinorVersion = PRCB_MINOR_VERSION;

    /* Set the Build Type */
    Pcr->PrcbData.BuildType = 0;
#ifndef CONFIG_SMP
    Pcr->PrcbData.BuildType |= PRCB_BUILD_UNIPROCESSOR;
#endif
#if DBG
    Pcr->PrcbData.BuildType |= PRCB_BUILD_DEBUG;
#endif

    /* Set the Processor Number and current Processor Mask */
    Pcr->PrcbData.Number = (UCHAR)ProcessorNumber;
    Pcr->PrcbData.SetMember = 1 << ProcessorNumber;

    /* Set the PRCB for this Processor */
    KiProcessorBlock[ProcessorNumber] = Pcr->Prcb;

    /* Start us out at PASSIVE_LEVEL */
    Pcr->Irql = PASSIVE_LEVEL;

    /* Set the GDI, IDT, TSS and DPC Stack */
    Pcr->GDT = (PVOID)Gdt;
    Pcr->IDT = Idt;
    Pcr->TSS = Tss;
    Pcr->TssCopy = Tss;
    Pcr->PrcbData.DpcStack = DpcStack;

    /* Setup the processor set */
    Pcr->PrcbData.MultiThreadProcessorSet = Pcr->PrcbData.SetMember;
}

static
CODE_SEG("INIT")
VOID
KiVerifyCpuFeatures(PKPRCB Prcb)
{
    CPU_INFO CpuInfo;

    // 1. Check CPUID support
    ULONG EFlags = __readeflags();

    /* XOR out the ID bit and update EFlags */
    ULONG NewEFlags = EFlags ^ EFLAGS_ID;
    __writeeflags(NewEFlags);

    /* Get them back and see if they were modified */
    NewEFlags = __readeflags();

    if (NewEFlags == EFlags)
    {
        /* The modification did not work, so CPUID is not supported. */
        KeBugCheckEx(UNSUPPORTED_PROCESSOR, 0x1, 0, 0, 0);
    }
    else
    {
        /* CPUID is supported. Set the ID Bit again. */
        EFlags |= EFLAGS_ID;
        __writeeflags(EFlags);
    }

    /* Peform CPUID 0 to see if CPUID 1 is supported */
    KiCpuId(&CpuInfo, 0);
    if (CpuInfo.Eax == 0)
    {
        // 0x1 - missing CPUID instruction
        KeBugCheckEx(UNSUPPORTED_PROCESSOR, 0x1, 0, 0, 0);
    }

    // 2. Detect and set the CPU Type
    KiSetProcessorType();

    if (Prcb->CpuType == 3)
        KeBugCheckEx(UNSUPPORTED_PROCESSOR, 0x386, 0, 0, 0);

    // 3. Finally, obtain CPU features.
    ULONG FeatureBits = KiGetFeatureBits();

    // 4. Verify it supports everything we need.
    if (!(FeatureBits & KF_RDTSC))
    {
        // 0x2 - missing CPUID features
        // second paramenter - edx flag which is missing
        KeBugCheckEx(UNSUPPORTED_PROCESSOR, 0x2, 0x00000010, 0, 0);
    }

    if (!(FeatureBits & KF_CMPXCHG8B))
    {
        KeBugCheckEx(UNSUPPORTED_PROCESSOR, 0x2, 0x00000100, 0, 0);
    }

    // Check x87 FPU is present. FIXME: put this into FeatureBits?
    KiCpuId(&CpuInfo, 1);

    if (!(CpuInfo.Edx & 0x00000001))
    {
        KeBugCheckEx(UNSUPPORTED_PROCESSOR, 0x2, 0x00000001, 0, 0);
    }

    // Set up FPU-related CR0 flags.
    ULONG Cr0 = __readcr0();
    // Disable emulation and monitoring.
    Cr0 &= ~(CR0_EM | CR0_MP);
    // Enable FPU exceptions.
    Cr0 |= CR0_NE;

    __writecr0(Cr0);

    // Check for Pentium FPU bug.
    if (KiIsNpxErrataPresent())
    {
        KeBugCheckEx(UNSUPPORTED_PROCESSOR, 0x2, 0x00000001, 0, 0);
    }

    // 5. Save feature bits.
    Prcb->FeatureBits = FeatureBits;
}

CODE_SEG("INIT")
VOID
NTAPI
KiInitializeKernel(IN PKPROCESS InitProcess,
                   IN PKTHREAD InitThread,
                   IN PVOID IdleStack,
                   IN PKPRCB Prcb,
                   IN CCHAR Number,
                   IN PLOADER_PARAMETER_BLOCK LoaderBlock)
{
    ULONG PageDirectory[2];
    PVOID DpcStack;
    KIRQL DummyIrql;

    /* Initialize the Power Management Support for this PRCB */
    PoInitializePrcb(Prcb);

    /* Set boot-level flags */
    if (Number == 0)
        KeFeatureBits = Prcb->FeatureBits;

    /* Set the default NX policy (opt-in) */
    SharedUserData->NXSupportPolicy = NX_SUPPORT_POLICY_OPTIN;

    /* Check if NPX is always on */
    if (strstr(KeLoaderBlock->LoadOptions, "NOEXECUTE=ALWAYSON"))
    {
        /* Set it always on */
        SharedUserData->NXSupportPolicy = NX_SUPPORT_POLICY_ALWAYSON;
        KeFeatureBits |= KF_NX_ENABLED;
    }
    else if (strstr(KeLoaderBlock->LoadOptions, "NOEXECUTE=OPTOUT"))
    {
        /* Set it in opt-out mode */
        SharedUserData->NXSupportPolicy = NX_SUPPORT_POLICY_OPTOUT;
        KeFeatureBits |= KF_NX_ENABLED;
    }
    else if ((strstr(KeLoaderBlock->LoadOptions, "NOEXECUTE=OPTIN")) ||
             (strstr(KeLoaderBlock->LoadOptions, "NOEXECUTE")))
    {
        /* Set the feature bits */
        KeFeatureBits |= KF_NX_ENABLED;
    }
    else if ((strstr(KeLoaderBlock->LoadOptions, "NOEXECUTE=ALWAYSOFF")) ||
             (strstr(KeLoaderBlock->LoadOptions, "EXECUTE")))
    {
        /* Set disabled mode */
        SharedUserData->NXSupportPolicy = NX_SUPPORT_POLICY_ALWAYSOFF;
        KeFeatureBits |= KF_NX_DISABLED;
    }

    /* Save CPU state */
    KiSaveProcessorControlState(&Prcb->ProcessorState);

#if DBG
    /* Print applied kernel features/policies and boot CPU features */
    if (Number == 0)
        KiReportCpuFeatures();
#endif

    /* Get cache line information for this CPU */
    KiGetCacheInformation();

    /* Initialize spinlocks and DPC data */
    KiInitSpinLocks(Prcb, Number);

    /* Set Node Data */
    Prcb->ParentNode = KeNodeBlock[0];
    Prcb->ParentNode->ProcessorMask |= Prcb->SetMember;

    /* Check if this is the Boot CPU */
    if (!Number)
    {
        /* Set boot-level flags */
        KeI386CpuType = Prcb->CpuType;
        KeI386CpuStep = Prcb->CpuStep;
        KeProcessorArchitecture = PROCESSOR_ARCHITECTURE_INTEL;
        KeProcessorLevel = (USHORT)Prcb->CpuType;
        if (Prcb->CpuID) KeProcessorRevision = Prcb->CpuStep;
        KeI386FxsrPresent = (KeFeatureBits & KF_FXSR) ? TRUE : FALSE;
        KeI386XMMIPresent = (KeFeatureBits & KF_XMMI) ? TRUE : FALSE;

        /* Set the current MP Master KPRCB to the Boot PRCB */
        Prcb->MultiThreadSetMaster = Prcb;

        /* Lower to APC_LEVEL */
        KeLowerIrql(APC_LEVEL);

        /* Initialize some spinlocks */
        KeInitializeSpinLock(&KiFreezeExecutionLock);
        KeInitializeSpinLock(&Ki486CompatibilityLock);

        /* Initialize portable parts of the OS */
        KiInitSystem();

        /* Initialize the Idle Process and the Process Listhead */
        InitializeListHead(&KiProcessListHead);
        PageDirectory[0] = 0;
        PageDirectory[1] = 0;
        KeInitializeProcess(InitProcess,
                            0,
                            MAXULONG_PTR,
                            PageDirectory,
                            FALSE);
        InitProcess->QuantumReset = MAXCHAR;
    }
    else
    {
        /* FIXME */
        DPRINT1("Starting CPU#%u - you are brave\n", Number);
    }

    /* Setup the Idle Thread */
    KeInitializeThread(InitProcess,
                       InitThread,
                       NULL,
                       NULL,
                       NULL,
                       NULL,
                       NULL,
                       IdleStack);
    InitThread->NextProcessor = Number;
    InitThread->Priority = HIGH_PRIORITY;
    InitThread->State = Running;
    InitThread->Affinity = 1 << Number;
    InitThread->WaitIrql = DISPATCH_LEVEL;
    InitProcess->ActiveProcessors |= 1 << Number;

    /* HACK for MmUpdatePageDir */
    ((PETHREAD)InitThread)->ThreadsProcess = (PEPROCESS)InitProcess;

    /* Set basic CPU Features that user mode can read */
    SharedUserData->ProcessorFeatures[PF_FLOATING_POINT_PRECISION_ERRATA] = FALSE;
    SharedUserData->ProcessorFeatures[PF_MMX_INSTRUCTIONS_AVAILABLE] =
        (KeFeatureBits & KF_MMX) ? TRUE: FALSE;
    SharedUserData->ProcessorFeatures[PF_COMPARE_EXCHANGE_DOUBLE] =
        (KeFeatureBits & KF_CMPXCHG8B) ? TRUE: FALSE;
    SharedUserData->ProcessorFeatures[PF_XMMI_INSTRUCTIONS_AVAILABLE] =
        ((KeFeatureBits & KF_FXSR) && (KeFeatureBits & KF_XMMI)) ? TRUE: FALSE;
    SharedUserData->ProcessorFeatures[PF_XMMI64_INSTRUCTIONS_AVAILABLE] =
        ((KeFeatureBits & KF_FXSR) && (KeFeatureBits & KF_XMMI64)) ? TRUE: FALSE;
    SharedUserData->ProcessorFeatures[PF_3DNOW_INSTRUCTIONS_AVAILABLE] =
        (KeFeatureBits & KF_3DNOW) ? TRUE: FALSE;
    SharedUserData->ProcessorFeatures[PF_RDTSC_INSTRUCTION_AVAILABLE] =
        (KeFeatureBits & KF_RDTSC) ? TRUE: FALSE;

    /* Set up the thread-related fields in the PRCB */
    Prcb->CurrentThread = InitThread;
    Prcb->NextThread = NULL;
    Prcb->IdleThread = InitThread;

    /* Initialize the Kernel Executive */
    ExpInitializeExecutive(Number, LoaderBlock);

    /* Only do this on the boot CPU */
    if (!Number)
    {
        /* Calculate the time reciprocal */
        KiTimeIncrementReciprocal =
            KiComputeReciprocal(KeMaximumIncrement,
                                &KiTimeIncrementShiftCount);

        /* Update DPC Values in case they got updated by the executive */
        Prcb->MaximumDpcQueueDepth = KiMaximumDpcQueueDepth;
        Prcb->MinimumDpcRate = KiMinimumDpcRate;
        Prcb->AdjustDpcThreshold = KiAdjustDpcThreshold;

        /* Allocate the DPC Stack */
        DpcStack = MmCreateKernelStack(FALSE, 0);
        if (!DpcStack) KeBugCheckEx(NO_PAGES_AVAILABLE, 1, 0, 0, 0);
        Prcb->DpcStack = DpcStack;

        /* Allocate the IOPM save area */
        Ki386IopmSaveArea = ExAllocatePoolWithTag(PagedPool,
                                                  IOPM_SIZE,
                                                  TAG_KERNEL);
        if (!Ki386IopmSaveArea)
        {
            /* Bugcheck. We need this for V86/VDM support. */
            KeBugCheckEx(NO_PAGES_AVAILABLE, 2, IOPM_SIZE, 0, 0);
        }
    }

    /* Raise to Dispatch */
    KeRaiseIrql(DISPATCH_LEVEL, &DummyIrql);

    /* Set the Idle Priority to 0. This will jump into Phase 1 */
    KeSetPriorityThread(InitThread, 0);

    /* If there's no thread scheduled, put this CPU in the Idle summary */
    KiAcquirePrcbLock(Prcb);
    if (!Prcb->NextThread) KiIdleSummary |= 1 << Number;
    KiReleasePrcbLock(Prcb);

    /* Raise back to HIGH_LEVEL and clear the PRCB for the loader block */
    KeRaiseIrql(HIGH_LEVEL, &DummyIrql);
    LoaderBlock->Prcb = 0;
}

CODE_SEG("INIT")
VOID
FASTCALL
KiGetMachineBootPointers(IN PKGDTENTRY *Gdt,
                         IN PKIDTENTRY *Idt,
                         IN PKIPCR *Pcr,
                         IN PKTSS *Tss)
{
    KDESCRIPTOR GdtDescriptor, IdtDescriptor;
    KGDTENTRY TssSelector, PcrSelector;
    USHORT Tr, Fs;

    /* Get GDT and IDT descriptors */
    Ke386GetGlobalDescriptorTable(&GdtDescriptor.Limit);
    __sidt(&IdtDescriptor.Limit);

    /* Save IDT and GDT */
    *Gdt = (PKGDTENTRY)GdtDescriptor.Base;
    *Idt = (PKIDTENTRY)IdtDescriptor.Base;

    /* Get TSS and FS Selectors */
    Tr = Ke386GetTr();
    Fs = Ke386GetFs();

    /* Get PCR Selector, mask it and get its GDT Entry */
    PcrSelector = *(PKGDTENTRY)((ULONG_PTR)*Gdt + (Fs & ~RPL_MASK));

    /* Get the KPCR itself */
    *Pcr = (PKIPCR)(ULONG_PTR)(PcrSelector.BaseLow |
                               PcrSelector.HighWord.Bytes.BaseMid << 16 |
                               PcrSelector.HighWord.Bytes.BaseHi << 24);

    /* Get TSS Selector, mask it and get its GDT Entry */
    TssSelector = *(PKGDTENTRY)((ULONG_PTR)*Gdt + (Tr & ~RPL_MASK));

    /* Get the KTSS itself */
    *Tss = (PKTSS)(ULONG_PTR)(TssSelector.BaseLow |
                              TssSelector.HighWord.Bytes.BaseMid << 16 |
                              TssSelector.HighWord.Bytes.BaseHi << 24);
}

CODE_SEG("INIT")
DECLSPEC_NORETURN
VOID
NTAPI
KiSystemStartupBootStack(VOID)
{
    PKTHREAD Thread;

    /* Initialize the kernel for the current CPU */
    KiInitializeKernel(&KiInitialProcess.Pcb,
                       (PKTHREAD)KeLoaderBlock->Thread,
                       (PVOID)(KeLoaderBlock->KernelStack & ~3),
                       (PKPRCB)__readfsdword(KPCR_PRCB),
                       KeNumberProcessors - 1,
                       KeLoaderBlock);

    /* Set the priority of this thread to 0 */
    Thread = KeGetCurrentThread();
    Thread->Priority = 0;

    /* Force interrupts enabled and lower IRQL back to DISPATCH_LEVEL */
    _enable();
    KeLowerIrql(DISPATCH_LEVEL);

    /* Set the right wait IRQL */
    Thread->WaitIrql = DISPATCH_LEVEL;

    /* Jump into the idle loop */
    KiIdleLoop();
}

static
VOID
KiMarkPageAsReadOnly(
    PVOID Address)
{
    PHARDWARE_PTE PointerPte;

    /* Make sure the address is page aligned */
    ASSERT(ALIGN_DOWN_POINTER_BY(Address, PAGE_SIZE) == Address);

    /* Get the PTE address */
    PointerPte = ((PHARDWARE_PTE)PTE_BASE) + ((ULONG_PTR)Address / PAGE_SIZE);
    ASSERT(PointerPte->Valid);
    ASSERT(PointerPte->Write);

    /* Set as read-only */
    PointerPte->Write = 0;

    /* Flush the TLB entry */
    __invlpg(Address);
}

CODE_SEG("INIT")
DECLSPEC_NORETURN
VOID
NTAPI
KiSystemStartup(IN PLOADER_PARAMETER_BLOCK LoaderBlock)
{
    ULONG Cpu;
    PKTHREAD InitialThread;
    ULONG InitialStack;
    PKGDTENTRY Gdt;
    PKIDTENTRY Idt;
    KIDTENTRY NmiEntry, DoubleFaultEntry;
    PKTSS Tss;
    PKIPCR Pcr;
    KIRQL DummyIrql;

    /* Boot cycles timestamp */
    BootCycles = __rdtsc();

    /* Save the loader block and get the current CPU */
    KeLoaderBlock = LoaderBlock;
    Cpu = KeNumberProcessors;
    if (!Cpu)
    {
        /* If this is the boot CPU, set FS and the CPU Number*/
        Ke386SetFs(KGDT_R0_PCR);
        __writefsdword(KPCR_PROCESSOR_NUMBER, Cpu);

        /* Set the initial stack and idle thread as well */
        LoaderBlock->KernelStack = (ULONG_PTR)P0BootStack;
        LoaderBlock->Thread = (ULONG_PTR)&KiInitialThread;
    }

    /* Save the initial thread and stack */
    InitialStack = LoaderBlock->KernelStack;
    InitialThread = (PKTHREAD)LoaderBlock->Thread;

    /* Clean the APC List Head */
    InitializeListHead(&InitialThread->ApcState.ApcListHead[KernelMode]);

    /* Initialize the machine type */
    KiInitializeMachineType();

    /* Skip initial setup if this isn't the Boot CPU */
    if (Cpu) goto AppCpuInit;

    /* Get GDT, IDT, PCR and TSS pointers */
    KiGetMachineBootPointers(&Gdt, &Idt, &Pcr, &Tss);

    /* Setup the TSS descriptors and entries */
    Ki386InitializeTss(Tss, Idt, Gdt);

    /* Initialize the PCR */
    RtlZeroMemory(Pcr, PAGE_SIZE);
    KiInitializePcr(Cpu,
                    Pcr,
                    Idt,
                    Gdt,
                    Tss,
                    InitialThread,
                    (PVOID)KiDoubleFaultStack);

    /* Set us as the current process */
    InitialThread->ApcState.Process = &KiInitialProcess.Pcb;

    /* Clear DR6/7 to cleanup bootloader debugging */
    __writefsdword(KPCR_TEB, 0);
    __writefsdword(KPCR_DR6, 0);
    __writefsdword(KPCR_DR7, 0);

    /* Setup the IDT */
    KeInitExceptions();

    /* Load Ring 3 selectors for DS/ES */
    Ke386SetDs(KGDT_R3_DATA | RPL_MASK);
    Ke386SetEs(KGDT_R3_DATA | RPL_MASK);

    /* Save NMI and double fault traps */
    RtlCopyMemory(&NmiEntry, &Idt[2], sizeof(KIDTENTRY));
    RtlCopyMemory(&DoubleFaultEntry, &Idt[8], sizeof(KIDTENTRY));

    /* Copy kernel's trap handlers */
    RtlCopyMemory(Idt,
                  (PVOID)KiIdtDescriptor.Base,
                  KiIdtDescriptor.Limit + 1);

    /* Restore NMI and double fault */
    RtlCopyMemory(&Idt[2], &NmiEntry, sizeof(KIDTENTRY));
    RtlCopyMemory(&Idt[8], &DoubleFaultEntry, sizeof(KIDTENTRY));

AppCpuInit:
    //TODO: We don't setup IPIs yet so freeze other processors here.
    if (Cpu)
    {
        KeMemoryBarrier();
        LoaderBlock->Prcb = 0;

        for (;;)
        {
            YieldProcessor();
        }
    }

    /* Loop until we can release the freeze lock */
    do
    {
        /* Loop until execution can continue */
        while (*(volatile PKSPIN_LOCK*)&KiFreezeExecutionLock == (PVOID)1);
    } while(InterlockedBitTestAndSet((PLONG)&KiFreezeExecutionLock, 0));

    /* Setup CPU-related fields */
    __writefsdword(KPCR_NUMBER, Cpu);
    __writefsdword(KPCR_SET_MEMBER, 1 << Cpu);
    __writefsdword(KPCR_SET_MEMBER_COPY, 1 << Cpu);
    __writefsdword(KPCR_PRCB_SET_MEMBER, 1 << Cpu);

    KiVerifyCpuFeatures(Pcr->Prcb);

    /* Initialize the Processor with HAL */
    HalInitializeProcessor(Cpu, KeLoaderBlock);

    /* Set active processors */
    KeActiveProcessors |= __readfsdword(KPCR_SET_MEMBER);
    KeNumberProcessors++;

    /* Check if this is the boot CPU */
    if (!Cpu)
    {
        /* Initialize debugging system */
        KdInitSystem(0, KeLoaderBlock);

        /* Check for break-in */
        if (KdPollBreakIn()) DbgBreakPointWithStatus(DBG_STATUS_CONTROL_C);

        /* Make the lowest page of the boot and double fault stack read-only */
        KiMarkPageAsReadOnly(P0BootStackData);
        KiMarkPageAsReadOnly(KiDoubleFaultStackData);
    }

    /* Raise to HIGH_LEVEL */
    KeRaiseIrql(HIGH_LEVEL, &DummyIrql);

    /* Switch to new kernel stack and start kernel bootstrapping */
    KiSwitchToBootStack(InitialStack & ~3);
}