cpu/kvm/base.cc

/*
 * Copyright (c) 2012 ARM Limited
 * All rights reserved
 *
 * The license below extends only to copyright in the software and shall
 * not be construed as granting a license to any other intellectual
 * property including but not limited to intellectual property relating
 * to a hardware implementation of the functionality of the software
 * licensed hereunder.  You may use the software subject to the license
 * terms below provided that you ensure that this notice is replicated
 * unmodified and in its entirety in all distributions of the software,
 * modified or unmodified, in source code or in binary form.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met: redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer;
 * redistributions in binary form must reproduce the above copyright
 * notice, this list of conditions and the following disclaimer in the
 * documentation and/or other materials provided with the distribution;
 * neither the name of the copyright holders nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * Authors: Andreas Sandberg
 */

#include <linux/kvm.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <unistd.h>

#include <cerrno>
#include <csignal>
#include <ostream>

#include "arch/utility.hh"
#include "cpu/kvm/base.hh"
#include "debug/Kvm.hh"
#include "debug/KvmIO.hh"
#include "debug/KvmRun.hh"
#include "params/BaseKvmCPU.hh"
#include "sim/process.hh"
#include "sim/system.hh"

/* Used by some KVM macros */
#define PAGE_SIZE pageSize

volatile bool timerOverflowed = false;

static void
onTimerOverflow(int signo, siginfo_t *si, void *data)
{
    timerOverflowed = true;
}

BaseKvmCPU::BaseKvmCPU(BaseKvmCPUParams *params)
    : BaseCPU(params),
      vm(*params->kvmVM),
      _status(Idle),
      dataPort(name() + ".dcache_port", this),
      instPort(name() + ".icache_port", this),
      threadContextDirty(true),
      kvmStateDirty(false),
      vcpuID(vm.allocVCPUID()), vcpuFD(-1), vcpuMMapSize(0),
      _kvmRun(NULL), mmioRing(NULL),
      pageSize(sysconf(_SC_PAGE_SIZE)),
      tickEvent(*this),
      hostFactor(params->hostFactor)
{
    if (pageSize == -1)
        panic("KVM: Failed to determine host page size (%i)\n",
              errno);

    thread = new SimpleThread(this, 0, params->system,
                              params->itb, params->dtb, params->isa[0]);
    thread->setStatus(ThreadContext::Halted);
    tc = thread->getTC();
    threadContexts.push_back(tc);

    setupCounters();
    setupSignalHandler();

    runTimer.reset(new PosixKvmTimer(KVM_TIMER_SIGNAL, CLOCK_MONOTONIC,
                                     params->hostFactor,
                                     params->clock));
}

BaseKvmCPU::~BaseKvmCPU()
{
    if (_kvmRun)
        munmap(_kvmRun, vcpuMMapSize);
    close(vcpuFD);
}

void
BaseKvmCPU::init()
{
    BaseCPU::init();

    if (numThreads != 1)
        fatal("KVM: Multithreading not supported");

    tc->initMemProxies(tc);

    // initialize CPU, including PC
    if (FullSystem && !switchedOut())
        TheISA::initCPU(tc, tc->contextId());

    mmio_req.setThreadContext(tc->contextId(), 0);
}

void
BaseKvmCPU::startup()
{
    Kvm &kvm(vm.kvm);

    BaseCPU::startup();

    assert(vcpuFD == -1);

    // Tell the VM that a CPU is about to start.
    vm.cpuStartup();

    // We can't initialize KVM CPUs in BaseKvmCPU::init() since we are
    // not guaranteed that the parent KVM VM has initialized at that
    // point. Initialize virtual CPUs here instead.
    vcpuFD = vm.createVCPU(vcpuID);

    // Map the KVM run structure */
    vcpuMMapSize = kvm.getVCPUMMapSize();
    _kvmRun = (struct kvm_run *)mmap(0, vcpuMMapSize,
                                     PROT_READ | PROT_WRITE, MAP_SHARED,
                                     vcpuFD, 0);
    if (_kvmRun == MAP_FAILED)
        panic("KVM: Failed to map run data structure\n");

    // Setup a pointer to the MMIO ring buffer if coalesced MMIO is
    // available. The offset into the KVM's communication page is
    // provided by the coalesced MMIO capability.
    int mmioOffset(kvm.capCoalescedMMIO());
    if (mmioOffset) {
        inform("KVM: Coalesced IO available\n");
        mmioRing = (struct kvm_coalesced_mmio_ring *)(
            (char *)_kvmRun + (mmioOffset * pageSize));
    } else {
        inform("KVM: Coalesced not supported by host OS\n");
    }
}

void
BaseKvmCPU::regStats()
{
    using namespace Stats;

    BaseCPU::regStats();

    numVMExits
        .name(name() + ".numVMExits")
        .desc("total number of KVM exits")
        ;

    numMMIO
        .name(name() + ".numMMIO")
        .desc("number of VM exits due to memory mapped IO")
        ;

    numCoalescedMMIO
        .name(name() + ".numCoalescedMMIO")
        .desc("number of coalesced memory mapped IO requests")
        ;

    numIO
        .name(name() + ".numIO")
        .desc("number of VM exits due to legacy IO")
        ;

    numHalt
        .name(name() + ".numHalt")
        .desc("number of VM exits due to wait for interrupt instructions")
        ;

    numInterrupts
        .name(name() + ".numInterrupts")
        .desc("number of interrupts delivered")
        ;

    numHypercalls
        .name(name() + ".numHypercalls")
        .desc("number of hypercalls")
        ;
}

void
BaseKvmCPU::serializeThread(std::ostream &os, ThreadID tid)
{
    // Update the thread context so we have something to serialize.
    syncThreadContext();

    assert(tid == 0);
    assert(_status == Idle);
    thread->serialize(os);
}

void
BaseKvmCPU::unserializeThread(Checkpoint *cp, const std::string &section,
                              ThreadID tid)
{
    assert(tid == 0);
    assert(_status == Idle);
    thread->unserialize(cp, section);
    threadContextDirty = true;
}

unsigned int
BaseKvmCPU::drain(DrainManager *dm)
{
    if (switchedOut())
        return 0;

    DPRINTF(Kvm, "drain\n");

    // De-schedule the tick event so we don't insert any more MMIOs
    // into the system while it is draining.
    if (tickEvent.scheduled())
        deschedule(tickEvent);

    _status = Idle;
    return 0;
}

void
BaseKvmCPU::drainResume()
{
    assert(!tickEvent.scheduled());

    // We might have been switched out. In that case, we don't need to
    // do anything.
    if (switchedOut())
        return;

    DPRINTF(Kvm, "drainResume\n");
    verifyMemoryMode();

    // The tick event is de-scheduled as a part of the draining
    // process. Re-schedule it if the thread context is active.
    if (tc->status() == ThreadContext::Active) {
        schedule(tickEvent, nextCycle());
        _status = Running;
    } else {
        _status = Idle;
    }
}

void
BaseKvmCPU::switchOut()
{
    DPRINTF(Kvm, "switchOut\n");

    // Make sure to update the thread context in case, the new CPU
    // will need to access it.
    syncThreadContext();

    BaseCPU::switchOut();

    // We should have drained prior to executing a switchOut, which
    // means that the tick event shouldn't be scheduled and the CPU is
    // idle.
    assert(!tickEvent.scheduled());
    assert(_status == Idle);
}

void
BaseKvmCPU::takeOverFrom(BaseCPU *cpu)
{
    DPRINTF(Kvm, "takeOverFrom\n");

    BaseCPU::takeOverFrom(cpu);

    // We should have drained prior to executing a switchOut, which
    // means that the tick event shouldn't be scheduled and the CPU is
    // idle.
    assert(!tickEvent.scheduled());
    assert(_status == Idle);
    assert(threadContexts.size() == 1);

    // The BaseCPU updated the thread context, make sure that we
    // synchronize next time we enter start the CPU.
    threadContextDirty = true;
}

void
BaseKvmCPU::verifyMemoryMode() const
{
    if (!(system->isAtomicMode() && system->bypassCaches())) {
        fatal("The KVM-based CPUs requires the memory system to be in the "
              "'atomic_noncaching' mode.\n");
    }
}

void
BaseKvmCPU::wakeup()
{
    DPRINTF(Kvm, "wakeup()\n");

    if (thread->status() != ThreadContext::Suspended)
        return;

    thread->activate();
}

void
BaseKvmCPU::activateContext(ThreadID thread_num, Cycles delay)
{
    DPRINTF(Kvm, "ActivateContext %d (%d cycles)\n", thread_num, delay);

    assert(thread_num == 0);
    assert(thread);

    assert(_status == Idle);
    assert(!tickEvent.scheduled());

    numCycles += ticksToCycles(thread->lastActivate - thread->lastSuspend)
        * hostFactor;

    schedule(tickEvent, clockEdge(delay));
    _status = Running;
}


void
BaseKvmCPU::suspendContext(ThreadID thread_num)
{
    DPRINTF(Kvm, "SuspendContext %d\n", thread_num);

    assert(thread_num == 0);
    assert(thread);

    if (_status == Idle)
        return;

    assert(_status == Running);

    // The tick event may no be scheduled if the quest has requested
    // the monitor to wait for interrupts. The normal CPU models can
    // get their tick events descheduled by quiesce instructions, but
    // that can't happen here.
    if (tickEvent.scheduled())
        deschedule(tickEvent);

    _status = Idle;
}

void
BaseKvmCPU::deallocateContext(ThreadID thread_num)
{
    // for now, these are equivalent
    suspendContext(thread_num);
}

void
BaseKvmCPU::haltContext(ThreadID thread_num)
{
    // for now, these are equivalent
    suspendContext(thread_num);
}

ThreadContext *
BaseKvmCPU::getContext(int tn)
{
    assert(tn == 0);
    syncThreadContext();
    return tc;
}


Counter
BaseKvmCPU::totalInsts() const
{
    return hwInstructions.read();
}

Counter
BaseKvmCPU::totalOps() const
{
    hack_once("Pretending totalOps is equivalent to totalInsts()\n");
    return hwInstructions.read();
}

void
BaseKvmCPU::dump()
{
    inform("State dumping not implemented.");
}

void
BaseKvmCPU::tick()
{
    assert(_status == Running);

    DPRINTF(KvmRun, "Entering KVM...\n");

    Tick ticksToExecute(mainEventQueue.nextTick() - curTick());
    Tick ticksExecuted(kvmRun(ticksToExecute));

    Tick delay(ticksExecuted + handleKvmExit());

    switch (_status) {
      case Running:
        schedule(tickEvent, clockEdge(ticksToCycles(delay)));
        break;

      default:
        /* The CPU is halted or waiting for an interrupt from a
         * device. Don't start it. */
        break;
    }
}

Tick
BaseKvmCPU::kvmRun(Tick ticks)
{
    uint64_t baseCycles(hwCycles.read());
    uint64_t baseInstrs(hwInstructions.read());

    // We might need to update the KVM state.
    syncKvmState();
    // Entering into KVM implies that we'll have to reload the thread
    // context from KVM if we want to access it. Flag the KVM state as
    // dirty with respect to the cached thread context.
    kvmStateDirty = true;

    if (ticks < runTimer->resolution()) {
        DPRINTF(KvmRun, "KVM: Adjusting tick count (%i -> %i)\n",
                ticks, runTimer->resolution());
        ticks = runTimer->resolution();
    }

    DPRINTF(KvmRun, "KVM: Executing for %i ticks\n", ticks);
    timerOverflowed = false;
    runTimer->arm(ticks);
    startCounters();
    if (ioctl(KVM_RUN) == -1) {
        if (errno != EINTR)
            panic("KVM: Failed to start virtual CPU (errno: %i)\n",
                  errno);
    }
    stopCounters();
    runTimer->disarm();

    uint64_t cyclesExecuted(hwCycles.read() - baseCycles);
    Tick ticksExecuted(runTimer->ticksFromHostCycles(cyclesExecuted));

    if (ticksExecuted < ticks &&
        timerOverflowed &&
        _kvmRun->exit_reason == KVM_EXIT_INTR) {
        // TODO: We should probably do something clever here...
        warn("KVM: Early timer event, requested %i ticks but got %i ticks.\n",
             ticks, ticksExecuted);
    }

    numCycles += cyclesExecuted * hostFactor;
    ++numVMExits;

    DPRINTF(KvmRun, "KVM: Executed %i instructions in %i cycles (%i ticks, sim cycles: %i).\n",
            hwInstructions.read() - baseInstrs,
            cyclesExecuted,
            ticksExecuted,
            cyclesExecuted * hostFactor);

    return ticksExecuted + flushCoalescedMMIO();
}

void
BaseKvmCPU::kvmNonMaskableInterrupt()
{
    ++numInterrupts;
    if (ioctl(KVM_NMI) == -1)
        panic("KVM: Failed to deliver NMI to virtual CPU\n");
}

void
BaseKvmCPU::kvmInterrupt(const struct kvm_interrupt &interrupt)
{
    ++numInterrupts;
    if (ioctl(KVM_INTERRUPT, (void *)&interrupt) == -1)
        panic("KVM: Failed to deliver interrupt to virtual CPU\n");
}

void
BaseKvmCPU::getRegisters(struct kvm_regs &regs) const
{
    if (ioctl(KVM_GET_REGS, &regs) == -1)
        panic("KVM: Failed to get guest registers\n");
}

void
BaseKvmCPU::setRegisters(const struct kvm_regs &regs)
{
    if (ioctl(KVM_SET_REGS, (void *)&regs) == -1)
        panic("KVM: Failed to set guest registers\n");
}

void
BaseKvmCPU::getSpecialRegisters(struct kvm_sregs &regs) const
{
    if (ioctl(KVM_GET_SREGS, &regs) == -1)
        panic("KVM: Failed to get guest special registers\n");
}

void
BaseKvmCPU::setSpecialRegisters(const struct kvm_sregs &regs)
{
    if (ioctl(KVM_SET_SREGS, (void *)&regs) == -1)
        panic("KVM: Failed to set guest special registers\n");
}

void
BaseKvmCPU::getFPUState(struct kvm_fpu &state) const
{
    if (ioctl(KVM_GET_FPU, &state) == -1)
        panic("KVM: Failed to get guest FPU state\n");
}

void
BaseKvmCPU::setFPUState(const struct kvm_fpu &state)
{
    if (ioctl(KVM_SET_FPU, (void *)&state) == -1)
        panic("KVM: Failed to set guest FPU state\n");
}


void
BaseKvmCPU::setOneReg(uint64_t id, const void *addr)
{
#ifdef KVM_SET_ONE_REG
    struct kvm_one_reg reg;
    reg.id = id;
    reg.addr = (uint64_t)addr;

    if (ioctl(KVM_SET_ONE_REG, &reg) == -1) {
        panic("KVM: Failed to set register (0x%x) value (errno: %i)\n",
              id, errno);
    }
#else
    panic("KVM_SET_ONE_REG is unsupported on this platform.\n");
#endif
}

void
BaseKvmCPU::getOneReg(uint64_t id, void *addr) const
{
#ifdef KVM_GET_ONE_REG
    struct kvm_one_reg reg;
    reg.id = id;
    reg.addr = (uint64_t)addr;

    if (ioctl(KVM_GET_ONE_REG, &reg) == -1) {
        panic("KVM: Failed to get register (0x%x) value (errno: %i)\n",
              id, errno);
    }
#else
    panic("KVM_GET_ONE_REG is unsupported on this platform.\n");
#endif
}

std::string
BaseKvmCPU::getAndFormatOneReg(uint64_t id) const
{
#ifdef KVM_GET_ONE_REG
    std::ostringstream ss;

    ss.setf(std::ios::hex, std::ios::basefield);
    ss.setf(std::ios::showbase);
#define HANDLE_INTTYPE(len)                      \
    case KVM_REG_SIZE_U ## len: {                \
        uint ## len ## _t value;                 \
        getOneReg(id, &value);                   \
        ss << value;                             \
    }  break

#define HANDLE_ARRAY(len)                       \
    case KVM_REG_SIZE_U ## len: {               \
        uint8_t value[len / 8];                 \
        getOneReg(id, value);                   \
        ss << "[" << value[0];                  \
        for (int i = 1; i < len  / 8; ++i)      \
            ss << ", " << value[i];             \
        ss << "]";                              \
      } break

    switch (id & KVM_REG_SIZE_MASK) {
        HANDLE_INTTYPE(8);
        HANDLE_INTTYPE(16);
        HANDLE_INTTYPE(32);
        HANDLE_INTTYPE(64);
        HANDLE_ARRAY(128);
        HANDLE_ARRAY(256);
        HANDLE_ARRAY(512);
        HANDLE_ARRAY(1024);
      default:
        ss << "??";
    }

#undef HANDLE_INTTYPE
#undef HANDLE_ARRAY

    return ss.str();
#else
    panic("KVM_GET_ONE_REG is unsupported on this platform.\n");
#endif
}

void
BaseKvmCPU::syncThreadContext()
{
    if (!kvmStateDirty)
        return;

    assert(!threadContextDirty);

    updateThreadContext();
    kvmStateDirty = false;
}

void
BaseKvmCPU::syncKvmState()
{
    if (!threadContextDirty)
        return;

    assert(!kvmStateDirty);

    updateKvmState();
    threadContextDirty = false;
}

Tick
BaseKvmCPU::handleKvmExit()
{
    DPRINTF(KvmRun, "handleKvmExit (exit_reason: %i)\n", _kvmRun->exit_reason);

    switch (_kvmRun->exit_reason) {
      case KVM_EXIT_UNKNOWN:
        return handleKvmExitUnknown();

      case KVM_EXIT_EXCEPTION:
        return handleKvmExitException();

      case KVM_EXIT_IO:
        ++numIO;
        return handleKvmExitIO();

      case KVM_EXIT_HYPERCALL:
        ++numHypercalls;
        return handleKvmExitHypercall();

      case KVM_EXIT_HLT:
        /* The guest has halted and is waiting for interrupts */
        DPRINTF(Kvm, "handleKvmExitHalt\n");
        ++numHalt;

        // Suspend the thread until the next interrupt arrives
        thread->suspend();

        // This is actually ignored since the thread is suspended.
        return 0;

      case KVM_EXIT_MMIO:
        /* Service memory mapped IO requests */
        DPRINTF(KvmIO, "KVM: Handling MMIO (w: %u, addr: 0x%x, len: %u)\n",
                _kvmRun->mmio.is_write,
                _kvmRun->mmio.phys_addr, _kvmRun->mmio.len);

        ++numMMIO;
        return doMMIOAccess(_kvmRun->mmio.phys_addr, _kvmRun->mmio.data,
                            _kvmRun->mmio.len, _kvmRun->mmio.is_write);

      case KVM_EXIT_IRQ_WINDOW_OPEN:
        return handleKvmExitIRQWindowOpen();

      case KVM_EXIT_FAIL_ENTRY:
        return handleKvmExitFailEntry();

      case KVM_EXIT_INTR:
        /* KVM was interrupted by a signal, restart it in the next
         * tick. */
        return 0;

      case KVM_EXIT_INTERNAL_ERROR:
        panic("KVM: Internal error (suberror: %u)\n",
              _kvmRun->internal.suberror);

      default:
        panic("KVM: Unexpected exit (exit_reason: %u)\n", _kvmRun->exit_reason);
    }
}

Tick
BaseKvmCPU::handleKvmExitIO()
{
    panic("KVM: Unhandled guest IO (dir: %i, size: %i, port: 0x%x, count: %i)\n",
          _kvmRun->io.direction, _kvmRun->io.size,
          _kvmRun->io.port, _kvmRun->io.count);
}

Tick
BaseKvmCPU::handleKvmExitHypercall()
{
    panic("KVM: Unhandled hypercall\n");
}

Tick
BaseKvmCPU::handleKvmExitIRQWindowOpen()
{
    warn("KVM: Unhandled IRQ window.\n");
    return 0;
}


Tick
BaseKvmCPU::handleKvmExitUnknown()
{
    panic("KVM: Unknown error when starting vCPU (hw reason: 0x%llx)\n",
          _kvmRun->hw.hardware_exit_reason);
}

Tick
BaseKvmCPU::handleKvmExitException()
{
    panic("KVM: Got exception when starting vCPU "
          "(exception: %u, error_code: %u)\n",
          _kvmRun->ex.exception, _kvmRun->ex.error_code);
}

Tick
BaseKvmCPU::handleKvmExitFailEntry()
{
    panic("KVM: Failed to enter virtualized mode (hw reason: 0x%llx)\n",
          _kvmRun->fail_entry.hardware_entry_failure_reason);
}

Tick
BaseKvmCPU::doMMIOAccess(Addr paddr, void *data, int size, bool write)
{
    mmio_req.setPhys(paddr, size,
                     0, /* flags */
                     dataMasterId());

    const MemCmd cmd(write ? MemCmd::WriteReq : MemCmd::ReadReq);
    Packet pkt(&mmio_req, cmd);
    pkt.dataStatic(data);
    return dataPort.sendAtomic(&pkt);
}

int
BaseKvmCPU::ioctl(int request, long p1) const
{
    if (vcpuFD == -1)
        panic("KVM: CPU ioctl called before initialization\n");

    return ::ioctl(vcpuFD, request, p1);
}

Tick
BaseKvmCPU::flushCoalescedMMIO()
{
    if (!mmioRing)
        return 0;

    DPRINTF(KvmIO, "KVM: Flushing the coalesced MMIO ring buffer\n");

    // TODO: We might need to do synchronization when we start to
    // support multiple CPUs
    Tick ticks(0);
    while (mmioRing->first != mmioRing->last) {
        struct kvm_coalesced_mmio &ent(
            mmioRing->coalesced_mmio[mmioRing->first]);

        DPRINTF(KvmIO, "KVM: Handling coalesced MMIO (addr: 0x%x, len: %u)\n",
                ent.phys_addr, ent.len);

        ++numCoalescedMMIO;
        ticks += doMMIOAccess(ent.phys_addr, ent.data, ent.len, true);

        mmioRing->first = (mmioRing->first + 1) % KVM_COALESCED_MMIO_MAX;
    }

    return ticks;
}

void
BaseKvmCPU::setupSignalHandler()
{
    struct sigaction sa;

    memset(&sa, 0, sizeof(sa));
    sa.sa_sigaction = onTimerOverflow;
    sa.sa_flags = SA_SIGINFO | SA_RESTART;
    if (sigaction(KVM_TIMER_SIGNAL, &sa, NULL) == -1)
        panic("KVM: Failed to setup vCPU signal handler\n");
}

void
BaseKvmCPU::setupCounters()
{
    DPRINTF(Kvm, "Attaching cycle counter...\n");
    PerfKvmCounterConfig cfgCycles(PERF_TYPE_HARDWARE,
                                PERF_COUNT_HW_CPU_CYCLES);
    cfgCycles.disabled(true)
        .pinned(true);
    hwCycles.attach(cfgCycles,
                    0); // TID (0 => currentThread)

    DPRINTF(Kvm, "Attaching instruction counter...\n");
    PerfKvmCounterConfig cfgInstructions(PERF_TYPE_HARDWARE,
                                      PERF_COUNT_HW_INSTRUCTIONS);
    hwInstructions.attach(cfgInstructions,
                          0, // TID (0 => currentThread)
                          hwCycles);
}

void
BaseKvmCPU::startCounters()
{
    // We only need to start/stop the hwCycles counter since hwCycles
    // and hwInstructions are a counter group with hwCycles as the
    // group leader.
    hwCycles.start();
}

void
BaseKvmCPU::stopCounters()
{
    hwCycles.stop();
}