tlb.cc

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/*
 * Copyright (c) 2011-2021 Advanced Micro Devices, Inc.
 * All rights reserved.
 *
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 * modification, are permitted provided that the following conditions are met:
 *
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 * this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 * this list of conditions and the following disclaimer in the documentation
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#include "arch/amdgpu/common/tlb.hh"
 
#include <cmath>
#include <cstring>
 
#include "arch/amdgpu/common/gpu_translation_state.hh"
#include "arch/x86/faults.hh"
#include "arch/x86/insts/microldstop.hh"
#include "arch/x86/page_size.hh"
#include "arch/x86/pagetable.hh"
#include "arch/x86/pagetable_walker.hh"
#include "arch/x86/regs/misc.hh"
#include "arch/x86/regs/msr.hh"
#include "arch/x86/regs/segment.hh"
#include "arch/x86/x86_traits.hh"
#include "base/bitfield.hh"
#include "base/logging.hh"
#include "base/output.hh"
#include "base/trace.hh"
#include "cpu/base.hh"
#include "cpu/thread_context.hh"
#include "debug/GPUPrefetch.hh"
#include "debug/GPUTLB.hh"
#include "mem/packet_access.hh"
#include "mem/page_table.hh"
#include "mem/request.hh"
#include "sim/process.hh"
#include "sim/pseudo_inst.hh"
 
namespace gem5
{
namespace X86ISA
{
 
    GpuTLB::GpuTLB(const Params &p)
        : ClockedObject(p), configAddress(0), size(p.size),
          cleanupEvent([this]{ cleanup(); }, name(), false,
                       Event::Maximum_Pri),
          exitEvent([this]{ exitCallback(); }, name()), stats(this)
    {
        assoc = p.assoc;
        assert(assoc <= size);
        numSets = size/assoc;
        allocationPolicy = p.allocationPolicy;
        hasMemSidePort = false;
        accessDistance = p.accessDistance;
 
        tlb.assign(size, TlbEntry());
 
        freeList.resize(numSets);
        entryList.resize(numSets);
 
        for (int set = 0; set < numSets; ++set) {
            for (int way = 0; way < assoc; ++way) {
                int x = set * assoc + way;
                freeList[set].push_back(&tlb.at(x));
            }
        }
 
        FA = (size == assoc);
 
        setMask = numSets - 1;
 
        maxCoalescedReqs = p.maxOutstandingReqs;
 
        // Do not allow maxCoalescedReqs to be more than the TLB associativity
        if (maxCoalescedReqs > assoc) {
            maxCoalescedReqs = assoc;
            cprintf("Forcing maxCoalescedReqs to %d (TLB assoc.) \n", assoc);
        }
 
        outstandingReqs = 0;
        hitLatency = p.hitLatency;
        missLatency1 = p.missLatency1;
        missLatency2 = p.missLatency2;
 
        // create the response ports based on the number of connected ports
        for (size_t i = 0; i < p.port_cpu_side_ports_connection_count; ++i) {
            cpuSidePort.push_back(new CpuSidePort(csprintf("%s-port%d",
                                  name(), i), this, i));
        }
 
        // create the request ports based on the number of connected ports
        for (size_t i = 0; i < p.port_mem_side_ports_connection_count; ++i) {
            memSidePort.push_back(new MemSidePort(csprintf("%s-port%d",
                                  name(), i), this, i));
        }
    }
 
    // fixme: this is never called?
    GpuTLB::~GpuTLB()
    {
        // make sure all the hash-maps are empty
        assert(translationReturnEvent.empty());
    }
 
    Port &
    GpuTLB::getPort(const std::string &if_name, PortID idx)
    {
        if (if_name == "cpu_side_ports") {
            if (idx >= static_cast<PortID>(cpuSidePort.size())) {
                panic("TLBCoalescer::getPort: unknown index %d\n", idx);
            }
 
            return *cpuSidePort[idx];
        } else if (if_name == "mem_side_ports") {
            if (idx >= static_cast<PortID>(memSidePort.size())) {
                panic("TLBCoalescer::getPort: unknown index %d\n", idx);
            }
 
            hasMemSidePort = true;
 
            return *memSidePort[idx];
        } else {
            panic("TLBCoalescer::getPort: unknown port %s\n", if_name);
        }
    }
 
    TlbEntry*
    GpuTLB::insert(Addr vpn, TlbEntry &entry)
    {
        TlbEntry *newEntry = nullptr;
 
        int set = (vpn >> PageShift) & setMask;
 
        if (!freeList[set].empty()) {
            newEntry = freeList[set].front();
            freeList[set].pop_front();
        } else {
            newEntry = entryList[set].back();
            entryList[set].pop_back();
        }
 
        *newEntry = entry;
        newEntry->vaddr = vpn;
        entryList[set].push_front(newEntry);
 
        return newEntry;
    }
 
    GpuTLB::EntryList::iterator
    GpuTLB::lookupIt(Addr va, bool update_lru)
    {
        int set = (va >> PageShift) & setMask;
 
        if (FA) {
            assert(!set);
        }
 
        auto entry = entryList[set].begin();
        for (; entry != entryList[set].end(); ++entry) {
            int page_size = (*entry)->size();
 
            if ((*entry)->vaddr <= va && (*entry)->vaddr + page_size > va) {
                DPRINTF(GPUTLB, "Matched vaddr %#x to entry starting at %#x "
                        "with size %#x.\n", va, (*entry)->vaddr, page_size);
 
                if (update_lru) {
                    entryList[set].push_front(*entry);
                    entryList[set].erase(entry);
                    entry = entryList[set].begin();
                }
 
                break;
            }
        }
 
        return entry;
    }
 
    TlbEntry*
    GpuTLB::lookup(Addr va, bool update_lru)
    {
        int set = (va >> PageShift) & setMask;
 
        auto entry = lookupIt(va, update_lru);
 
        if (entry == entryList[set].end())
            return nullptr;
        else
            return *entry;
    }
 
    void
    GpuTLB::invalidateAll()
    {
        DPRINTF(GPUTLB, "Invalidating all entries.\n");
 
        for (int i = 0; i < numSets; ++i) {
            while (!entryList[i].empty()) {
                TlbEntry *entry = entryList[i].front();
                entryList[i].pop_front();
                freeList[i].push_back(entry);
            }
        }
    }
 
    void
    GpuTLB::setConfigAddress(uint32_t addr)
    {
        configAddress = addr;
    }
 
    void
    GpuTLB::invalidateNonGlobal()
    {
        DPRINTF(GPUTLB, "Invalidating all non global entries.\n");
 
        for (int i = 0; i < numSets; ++i) {
            for (auto entryIt = entryList[i].begin();
                 entryIt != entryList[i].end();) {
                if (!(*entryIt)->global) {
                    freeList[i].push_back(*entryIt);
                    entryList[i].erase(entryIt++);
                } else {
                    ++entryIt;
                }
            }
        }
    }
 
    void
    GpuTLB::demapPage(Addr va, uint64_t asn)
    {
 
        int set = (va >> PageShift) & setMask;
        auto entry = lookupIt(va, false);
 
        if (entry != entryList[set].end()) {
            freeList[set].push_back(*entry);
            entryList[set].erase(entry);
        }
    }
 
 
 
    namespace
    {
 
    Cycles
    localMiscRegAccess(bool read, RegIndex regNum,
                       ThreadContext *tc, PacketPtr pkt)
    {
        if (read) {
            RegVal data = htole(tc->readMiscReg(regNum));
            // Make sure we don't trot off the end of data.
            pkt->setData((uint8_t *)&data);
        } else {
            RegVal data = htole(tc->readMiscRegNoEffect(regNum));
            tc->setMiscReg(regNum, letoh(data));
        }
        return Cycles(1);
    }
 
    } // anonymous namespace
 
    Fault
    GpuTLB::translateInt(bool read, const RequestPtr &req, ThreadContext *tc)
    {
        DPRINTF(GPUTLB, "Addresses references internal memory.\n");
        Addr vaddr = req->getVaddr();
        Addr prefix = (vaddr >> 3) & IntAddrPrefixMask;
 
        if (prefix == IntAddrPrefixCPUID) {
            panic("CPUID memory space not yet implemented!\n");
        } else if (prefix == IntAddrPrefixMSR) {
            vaddr = (vaddr >> 3) & ~IntAddrPrefixMask;
 
            RegIndex regNum;
            if (!msrAddrToIndex(regNum, vaddr))
                return std::make_shared<GeneralProtection>(0);
 
            req->setLocalAccessor(
                [read, regNum](ThreadContext *tc, PacketPtr pkt)
                {
                    return localMiscRegAccess(read, regNum, tc, pkt);
                }
            );
 
            return NoFault;
        } else if (prefix == IntAddrPrefixIO) {
            // TODO If CPL > IOPL or in virtual mode, check the I/O permission
            // bitmap in the TSS.
 
            Addr IOPort = vaddr & ~IntAddrPrefixMask;
            // Make sure the address fits in the expected 16 bit IO address
            // space.
            assert(!(IOPort & ~0xFFFF));
            if (IOPort == 0xCF8 && req->getSize() == 4) {
                req->setLocalAccessor(
                    [read](ThreadContext *tc, PacketPtr pkt)
                    {
                        return localMiscRegAccess(
                                read, misc_reg::PciConfigAddress, tc, pkt);
                    }
                );
            } else if ((IOPort & ~mask(2)) == 0xCFC) {
                req->setFlags(Request::UNCACHEABLE | Request::STRICT_ORDER);
                Addr configAddress =
                    tc->readMiscRegNoEffect(misc_reg::PciConfigAddress);
                if (bits(configAddress, 31, 31)) {
                    req->setPaddr(PhysAddrPrefixPciConfig |
                            mbits(configAddress, 30, 2) |
                            (IOPort & mask(2)));
                } else {
                    req->setPaddr(PhysAddrPrefixIO | IOPort);
                }
            } else {
                req->setFlags(Request::UNCACHEABLE | Request::STRICT_ORDER);
                req->setPaddr(PhysAddrPrefixIO | IOPort);
            }
            return NoFault;
        } else {
            panic("Access to unrecognized internal address space %#x.\n",
                  prefix);
        }
    }
 
    bool
    GpuTLB::tlbLookup(const RequestPtr &req,
                      ThreadContext *tc, bool update_stats)
    {
        bool tlb_hit = false;
    #ifndef NDEBUG
        uint32_t flags = req->getFlags();
        int seg = flags & SegmentFlagMask;
    #endif
 
        assert(seg != segment_idx::Ms);
        Addr vaddr = req->getVaddr();
        DPRINTF(GPUTLB, "TLB Lookup for vaddr %#x.\n", vaddr);
        HandyM5Reg m5Reg = tc->readMiscRegNoEffect(misc_reg::M5Reg);
 
        if (m5Reg.prot) {
            DPRINTF(GPUTLB, "In protected mode.\n");
            // make sure we are in 64-bit mode
            assert(m5Reg.mode == LongMode);
 
            // If paging is enabled, do the translation.
            if (m5Reg.paging) {
                DPRINTF(GPUTLB, "Paging enabled.\n");
                //update LRU stack on a hit
                TlbEntry *entry = lookup(vaddr, true);
 
                if (entry)
                    tlb_hit = true;
 
                if (!update_stats) {
                    // functional tlb access for memory initialization
                    // i.e., memory seeding or instr. seeding -> don't update
                    // TLB and stats
                    return tlb_hit;
                }
 
                stats.localNumTLBAccesses++;
 
                if (!entry) {
                    stats.localNumTLBMisses++;
                } else {
                    stats.localNumTLBHits++;
                }
            }
        }
 
        return tlb_hit;
    }
 
    Fault
    GpuTLB::translate(const RequestPtr &req, ThreadContext *tc,
                      Translation *translation, Mode mode,
                      bool &delayedResponse, bool timing, int &latency)
    {
        uint32_t flags = req->getFlags();
        int seg = flags & SegmentFlagMask;
        bool storeCheck = flags & Request::READ_MODIFY_WRITE;
 
        // If this is true, we're dealing with a request
        // to a non-memory address space.
        if (seg == segment_idx::Ms) {
            return translateInt(mode == Mode::Read, req, tc);
        }
 
        delayedResponse = false;
        Addr vaddr = req->getVaddr();
        DPRINTF(GPUTLB, "Translating vaddr %#x.\n", vaddr);
 
        HandyM5Reg m5Reg = tc->readMiscRegNoEffect(misc_reg::M5Reg);
 
        // If protected mode has been enabled...
        if (m5Reg.prot) {
            DPRINTF(GPUTLB, "In protected mode.\n");
            // If we're not in 64-bit mode, do protection/limit checks
            if (m5Reg.mode != LongMode) {
                DPRINTF(GPUTLB, "Not in long mode. Checking segment "
                        "protection.\n");
 
                // Check for a null segment selector.
                if (!(seg == segment_idx::Tsg || seg == segment_idx::Idtr ||
                    seg == segment_idx::Hs || seg == segment_idx::Ls)
                    && !tc->readMiscRegNoEffect(misc_reg::segSel(seg))) {
                    return std::make_shared<GeneralProtection>(0);
                }
 
                bool expandDown = false;
                SegAttr attr = tc->readMiscRegNoEffect(misc_reg::segAttr(seg));
 
                if (seg >= segment_idx::Es && seg <= segment_idx::Hs) {
                    if (!attr.writable && (mode == BaseMMU::Write ||
                        storeCheck))
                        return std::make_shared<GeneralProtection>(0);
 
                    if (!attr.readable && mode == BaseMMU::Read)
                        return std::make_shared<GeneralProtection>(0);
 
                    expandDown = attr.expandDown;
 
                }
 
                Addr base = tc->readMiscRegNoEffect(misc_reg::segBase(seg));
                Addr limit = tc->readMiscRegNoEffect(misc_reg::segLimit(seg));
                Addr logSize = (flags >> AddrSizeFlagShift) & AddrSizeFlagMask;
                int size = 8 << logSize;
 
                Addr offset = (vaddr - base) & mask(size);
                Addr endOffset = offset + req->getSize() - 1;
 
                if (expandDown) {
                    DPRINTF(GPUTLB, "Checking an expand down segment.\n");
                    warn_once("Expand down segments are untested.\n");
 
                    if (offset <= limit || endOffset <= limit)
                        return std::make_shared<GeneralProtection>(0);
                } else {
                    if (offset > limit || endOffset > limit)
                        return std::make_shared<GeneralProtection>(0);
                }
            }
 
            // If paging is enabled, do the translation.
            if (m5Reg.paging) {
                DPRINTF(GPUTLB, "Paging enabled.\n");
                // The vaddr already has the segment base applied.
                TlbEntry *entry = lookup(vaddr);
                stats.localNumTLBAccesses++;
 
                if (!entry) {
                    stats.localNumTLBMisses++;
                    if (timing) {
                        latency = missLatency1;
                    }
 
                    if (FullSystem) {
                        fatal("GpuTLB doesn't support full-system mode\n");
                    } else {
                        DPRINTF(GPUTLB, "Handling a TLB miss for address %#x "
                                "at pc %#x.\n", vaddr,
                                tc->pcState().instAddr());
 
                        Process *p = tc->getProcessPtr();
                        const EmulationPageTable::Entry *pte =
                            p->pTable->lookup(vaddr);
 
                        if (!pte && mode != BaseMMU::Execute) {
                            // penalize a "page fault" more
                            if (timing)
                                latency += missLatency2;
 
                            if (p->fixupFault(vaddr))
                                pte = p->pTable->lookup(vaddr);
                        }
 
                        if (!pte) {
                            return std::make_shared<PageFault>(vaddr, true,
                                                               mode, true,
                                                               false);
                        } else {
                            Addr alignedVaddr = p->pTable->pageAlign(vaddr);
 
                            DPRINTF(GPUTLB, "Mapping %#x to %#x\n",
                                    alignedVaddr, pte->paddr);
 
                            TlbEntry gpuEntry(p->pid(), alignedVaddr,
                                              pte->paddr, false, false);
                            entry = insert(alignedVaddr, gpuEntry);
                        }
 
                        DPRINTF(GPUTLB, "Miss was serviced.\n");
                    }
                } else {
                    stats.localNumTLBHits++;
 
                    if (timing) {
                        latency = hitLatency;
                    }
                }
 
                // Do paging protection checks.
                bool inUser = m5Reg.cpl == 3 && !(flags & CPL0FlagBit);
 
                CR0 cr0 = tc->readMiscRegNoEffect(misc_reg::Cr0);
                bool badWrite = (!entry->writable && (inUser || cr0.wp));
 
                if ((inUser && !entry->user) || (mode == BaseMMU::Write &&
                     badWrite)) {
                    // The page must have been present to get into the TLB in
                    // the first place. We'll assume the reserved bits are
                    // fine even though we're not checking them.
                    return std::make_shared<PageFault>(vaddr, true, mode,
                                                       inUser, false);
                }
 
                if (storeCheck && badWrite) {
                    // This would fault if this were a write, so return a page
                    // fault that reflects that happening.
                    return std::make_shared<PageFault>(vaddr, true,
                                                       BaseMMU::Write,
                                                       inUser, false);
                }
 
 
                DPRINTF(GPUTLB, "Entry found with paddr %#x, doing protection "
                        "checks.\n", entry->paddr);
 
                int page_size = entry->size();
                Addr paddr = entry->paddr | (vaddr & (page_size - 1));
                DPRINTF(GPUTLB, "Translated %#x -> %#x.\n", vaddr, paddr);
                req->setPaddr(paddr);
 
                if (entry->uncacheable)
                    req->setFlags(Request::UNCACHEABLE);
            } else {
                //Use the address which already has segmentation applied.
                DPRINTF(GPUTLB, "Paging disabled.\n");
                DPRINTF(GPUTLB, "Translated %#x -> %#x.\n", vaddr, vaddr);
                req->setPaddr(vaddr);
            }
        } else {
            // Real mode
            DPRINTF(GPUTLB, "In real mode.\n");
            DPRINTF(GPUTLB, "Translated %#x -> %#x.\n", vaddr, vaddr);
            req->setPaddr(vaddr);
        }
 
        // Check for an access to the local APIC
        if (FullSystem) {
            LocalApicBase localApicBase =
                tc->readMiscRegNoEffect(misc_reg::ApicBase);
 
            Addr baseAddr = localApicBase.base * PageBytes;
            Addr paddr = req->getPaddr();
 
            if (baseAddr <= paddr && baseAddr + PageBytes > paddr) {
                // Force the access to be uncacheable.
                req->setFlags(Request::UNCACHEABLE);
                req->setPaddr(x86LocalAPICAddress(tc->contextId(),
                                                  paddr - baseAddr));
            }
        }
 
        return NoFault;
    };
 
    Fault
    GpuTLB::translateAtomic(const RequestPtr &req, ThreadContext *tc,
                            Mode mode, int &latency)
    {
        bool delayedResponse;
 
        return GpuTLB::translate(req, tc, nullptr, mode, delayedResponse,
            false, latency);
    }
 
    void
    GpuTLB::translateTiming(const RequestPtr &req, ThreadContext *tc,
            Translation *translation, Mode mode, int &latency)
    {
        bool delayedResponse;
        assert(translation);
 
        Fault fault = GpuTLB::translate(req, tc, translation, mode,
                                        delayedResponse, true, latency);
 
        if (!delayedResponse)
            translation->finish(fault, req, tc, mode);
    }
 
    Walker*
    GpuTLB::getWalker()
    {
        return walker;
    }
 
 
    void
    GpuTLB::serialize(CheckpointOut &cp) const
    {
    }
 
    void
    GpuTLB::unserialize(CheckpointIn &cp)
    {
    }
 
    void
    GpuTLB::issueTLBLookup(PacketPtr pkt)
    {
        assert(pkt);
        assert(pkt->senderState);
 
        Addr virt_page_addr = roundDown(pkt->req->getVaddr(),
                                        X86ISA::PageBytes);
 
        GpuTranslationState *sender_state =
                safe_cast<GpuTranslationState*>(pkt->senderState);
 
        bool update_stats = !sender_state->isPrefetch;
        ThreadContext * tmp_tc = sender_state->tc;
 
        DPRINTF(GPUTLB, "Translation req. for virt. page addr %#x\n",
                virt_page_addr);
 
        int req_cnt = sender_state->reqCnt.back();
 
        if (update_stats) {
            stats.accessCycles -= (curTick() * req_cnt);
            stats.localCycles -= curTick();
            updatePageFootprint(virt_page_addr);
            stats.globalNumTLBAccesses += req_cnt;
        }
 
        tlbOutcome lookup_outcome = TLB_MISS;
        const RequestPtr &tmp_req = pkt->req;
 
        // Access the TLB and figure out if it's a hit or a miss.
        bool success = tlbLookup(tmp_req, tmp_tc, update_stats);
 
        if (success) {
            lookup_outcome = TLB_HIT;
            // Put the entry in SenderState
            TlbEntry *entry = lookup(tmp_req->getVaddr(), false);
            assert(entry);
 
            auto p = sender_state->tc->getProcessPtr();
            sender_state->tlbEntry =
                new TlbEntry(p->pid(), entry->vaddr, entry->paddr,
                             false, false);
 
            if (update_stats) {
                // the reqCnt has an entry per level, so its size tells us
                // which level we are in
                sender_state->hitLevel = sender_state->reqCnt.size();
                stats.globalNumTLBHits += req_cnt;
            }
        } else {
            if (update_stats)
                stats.globalNumTLBMisses += req_cnt;
        }
 
        /*
         * We now know the TLB lookup outcome (if it's a hit or a miss), as
         * well as the TLB access latency.
         *
         * We create and schedule a new TLBEvent which will help us take the
         * appropriate actions (e.g., update TLB on a hit, send request to
         * lower level TLB on a miss, or start a page walk if this was the
         * last-level TLB)
         */
        TLBEvent *tlb_event =
            new TLBEvent(this, virt_page_addr, lookup_outcome, pkt);
 
        if (translationReturnEvent.count(virt_page_addr)) {
            panic("Virtual Page Address %#x already has a return event\n",
                  virt_page_addr);
        }
 
        translationReturnEvent[virt_page_addr] = tlb_event;
        assert(tlb_event);
 
        DPRINTF(GPUTLB, "schedule translationReturnEvent @ curTick %d\n",
                curTick() + cyclesToTicks(Cycles(hitLatency)));
 
        schedule(tlb_event, curTick() + cyclesToTicks(Cycles(hitLatency)));
    }
 
    GpuTLB::TLBEvent::TLBEvent(GpuTLB* _tlb, Addr _addr,
        tlbOutcome tlb_outcome, PacketPtr _pkt)
            : Event(CPU_Tick_Pri), tlb(_tlb), virtPageAddr(_addr),
              outcome(tlb_outcome), pkt(_pkt)
    {
    }
 
    void
    GpuTLB::pagingProtectionChecks(ThreadContext *tc, PacketPtr pkt,
            TlbEntry * tlb_entry, Mode mode)
    {
        HandyM5Reg m5Reg = tc->readMiscRegNoEffect(misc_reg::M5Reg);
        uint32_t flags = pkt->req->getFlags();
        bool storeCheck = flags & Request::READ_MODIFY_WRITE;
 
        // Do paging protection checks.
        bool inUser = m5Reg.cpl == 3 && !(flags & CPL0FlagBit);
        CR0 cr0 = tc->readMiscRegNoEffect(misc_reg::Cr0);
 
        bool badWrite = (!tlb_entry->writable && (inUser || cr0.wp));
 
        if ((inUser && !tlb_entry->user) ||
            (mode == BaseMMU::Write && badWrite)) {
            // The page must have been present to get into the TLB in
            // the first place. We'll assume the reserved bits are
            // fine even though we're not checking them.
            panic("Page fault detected");
        }
 
        if (storeCheck && badWrite) {
            // This would fault if this were a write, so return a page
            // fault that reflects that happening.
            panic("Page fault detected");
        }
    }
 
    void
    GpuTLB::handleTranslationReturn(Addr virt_page_addr,
        tlbOutcome tlb_outcome, PacketPtr pkt)
    {
        assert(pkt);
        Addr vaddr = pkt->req->getVaddr();
 
        GpuTranslationState *sender_state =
            safe_cast<GpuTranslationState*>(pkt->senderState);
 
        ThreadContext *tc = sender_state->tc;
        Mode mode = sender_state->tlbMode;
 
        TlbEntry *local_entry, *new_entry;
 
        if (tlb_outcome == TLB_HIT) {
            DPRINTF(GPUTLB, "Translation Done - TLB Hit for addr %#x\n",
                vaddr);
            local_entry = safe_cast<TlbEntry *>(sender_state->tlbEntry);
        } else {
            DPRINTF(GPUTLB, "Translation Done - TLB Miss for addr %#x\n",
                    vaddr);
 
            new_entry = safe_cast<TlbEntry *>(sender_state->tlbEntry);
            assert(new_entry);
            local_entry = new_entry;
 
            if (allocationPolicy) {
                DPRINTF(GPUTLB, "allocating entry w/ addr %#x\n",
                        virt_page_addr);
 
                local_entry = insert(virt_page_addr, *new_entry);
            }
 
            assert(local_entry);
        }
 
        DPRINTF(GPUTLB, "Entry found with vaddr %#x,  doing protection checks "
                "while paddr was %#x.\n", local_entry->vaddr,
                local_entry->paddr);
 
        pagingProtectionChecks(tc, pkt, local_entry, mode);
        int page_size = local_entry->size();
        Addr paddr = local_entry->paddr | (vaddr & (page_size - 1));
        DPRINTF(GPUTLB, "Translated %#x -> %#x.\n", vaddr, paddr);
 
        // Since this packet will be sent through the cpu side port,
        // it must be converted to a response pkt if it is not one already
        if (pkt->isRequest()) {
            pkt->makeTimingResponse();
        }
 
        pkt->req->setPaddr(paddr);
 
        if (local_entry->uncacheable) {
             pkt->req->setFlags(Request::UNCACHEABLE);
        }
 
        //send packet back to coalescer
        cpuSidePort[0]->sendTimingResp(pkt);
        //schedule cleanup event
        cleanupQueue.push(virt_page_addr);
 
        // schedule this only once per cycle.
        // The check is required because we might have multiple translations
        // returning the same cycle
        // this is a maximum priority event and must be on the same cycle
        // as the cleanup event in TLBCoalescer to avoid a race with
        // IssueProbeEvent caused by TLBCoalescer::MemSidePort::recvReqRetry
        if (!cleanupEvent.scheduled())
            schedule(cleanupEvent, curTick());
    }
 
    void
    GpuTLB::translationReturn(Addr virtPageAddr, tlbOutcome outcome,
                              PacketPtr pkt)
    {
        DPRINTF(GPUTLB, "Triggered TLBEvent for addr %#x\n", virtPageAddr);
 
        assert(translationReturnEvent[virtPageAddr]);
        assert(pkt);
 
        GpuTranslationState *tmp_sender_state =
            safe_cast<GpuTranslationState*>(pkt->senderState);
 
        int req_cnt = tmp_sender_state->reqCnt.back();
        bool update_stats = !tmp_sender_state->isPrefetch;
 
 
        if (outcome == TLB_HIT) {
            handleTranslationReturn(virtPageAddr, TLB_HIT, pkt);
 
            if (update_stats) {
                stats.accessCycles += (req_cnt * curTick());
                stats.localCycles += curTick();
            }
 
        } else if (outcome == TLB_MISS) {
 
            DPRINTF(GPUTLB, "This is a TLB miss\n");
            if (update_stats) {
                stats.accessCycles += (req_cnt*curTick());
                stats.localCycles += curTick();
            }
 
            if (hasMemSidePort) {
                // the one cyle added here represent the delay from when we get
                // the reply back till when we propagate it to the coalescer
                // above.
                if (update_stats) {
                    stats.accessCycles += (req_cnt * 1);
                    stats.localCycles += 1;
                }
 
                if (!memSidePort[0]->sendTimingReq(pkt)) {
                    DPRINTF(GPUTLB, "Failed sending translation request to "
                            "lower level TLB for addr %#x\n", virtPageAddr);
 
                    memSidePort[0]->retries.push_back(pkt);
                } else {
                    DPRINTF(GPUTLB, "Sent translation request to lower level "
                            "TLB for addr %#x\n", virtPageAddr);
                }
            } else {
                //this is the last level TLB. Start a page walk
                DPRINTF(GPUTLB, "Last level TLB - start a page walk for "
                        "addr %#x\n", virtPageAddr);
 
                if (update_stats)
                    stats.pageTableCycles -= (req_cnt*curTick());
 
                TLBEvent *tlb_event = translationReturnEvent[virtPageAddr];
                assert(tlb_event);
                tlb_event->updateOutcome(PAGE_WALK);
                schedule(tlb_event,
                         curTick() + cyclesToTicks(Cycles(missLatency2)));
            }
        } else if (outcome == PAGE_WALK) {
            if (update_stats)
                stats.pageTableCycles += (req_cnt*curTick());
 
            // Need to access the page table and update the TLB
            DPRINTF(GPUTLB, "Doing a page walk for address %#x\n",
                    virtPageAddr);
 
            GpuTranslationState *sender_state =
                safe_cast<GpuTranslationState*>(pkt->senderState);
 
            Process *p = sender_state->tc->getProcessPtr();
            Addr vaddr = pkt->req->getVaddr();
 
            Addr alignedVaddr = p->pTable->pageAlign(vaddr);
            assert(alignedVaddr == virtPageAddr);
 
            const EmulationPageTable::Entry *pte = p->pTable->lookup(vaddr);
            if (!pte && sender_state->tlbMode != BaseMMU::Execute &&
                    p->fixupFault(vaddr)) {
                pte = p->pTable->lookup(vaddr);
            }
 
            if (pte) {
                DPRINTF(GPUTLB, "Mapping %#x to %#x\n", alignedVaddr,
                        pte->paddr);
 
                sender_state->tlbEntry =
                    new TlbEntry(p->pid(), virtPageAddr, pte->paddr, false,
                                 false);
            } else {
                sender_state->tlbEntry = nullptr;
            }
 
            handleTranslationReturn(virtPageAddr, TLB_MISS, pkt);
        } else if (outcome == MISS_RETURN) {
            handleTranslationReturn(virtPageAddr, TLB_MISS, pkt);
        } else {
            panic("Unexpected TLB outcome %d", outcome);
        }
    }
 
    void
    GpuTLB::TLBEvent::process()
    {
        tlb->translationReturn(virtPageAddr, outcome, pkt);
    }
 
    const char*
    GpuTLB::TLBEvent::description() const
    {
        return "trigger translationDoneEvent";
    }
 
    void
    GpuTLB::TLBEvent::updateOutcome(tlbOutcome _outcome)
    {
        outcome = _outcome;
    }
 
    Addr
    GpuTLB::TLBEvent::getTLBEventVaddr()
    {
        return virtPageAddr;
    }
 
    bool
    GpuTLB::CpuSidePort::recvTimingReq(PacketPtr pkt)
    {
        if (tlb->outstandingReqs < tlb->maxCoalescedReqs) {
            tlb->issueTLBLookup(pkt);
            // update number of outstanding translation requests
            tlb->outstandingReqs++;
            return true;
         } else {
            DPRINTF(GPUTLB, "Reached maxCoalescedReqs number %d\n",
                    tlb->outstandingReqs);
            return false;
         }
    }
 
    void
    GpuTLB::handleFuncTranslationReturn(PacketPtr pkt, tlbOutcome tlb_outcome)
    {
        GpuTranslationState *sender_state =
            safe_cast<GpuTranslationState*>(pkt->senderState);
 
        ThreadContext *tc = sender_state->tc;
        Mode mode = sender_state->tlbMode;
        Addr vaddr = pkt->req->getVaddr();
 
        TlbEntry *local_entry, *new_entry;
 
        if (tlb_outcome == TLB_HIT) {
            DPRINTF(GPUTLB, "Functional Translation Done - TLB hit for addr "
                    "%#x\n", vaddr);
 
            local_entry = safe_cast<TlbEntry *>(sender_state->tlbEntry);
        } else {
            DPRINTF(GPUTLB, "Functional Translation Done - TLB miss for addr "
                    "%#x\n", vaddr);
 
            new_entry = safe_cast<TlbEntry *>(sender_state->tlbEntry);
            assert(new_entry);
            local_entry = new_entry;
 
            if (allocationPolicy) {
                Addr virt_page_addr = roundDown(vaddr, X86ISA::PageBytes);
 
                DPRINTF(GPUTLB, "allocating entry w/ addr %#x\n",
                        virt_page_addr);
 
                local_entry = insert(virt_page_addr, *new_entry);
            }
 
            assert(local_entry);
        }
 
        DPRINTF(GPUTLB, "Entry found with vaddr %#x, doing protection checks "
                "while paddr was %#x.\n", local_entry->vaddr,
                local_entry->paddr);
 
        if (!sender_state->isPrefetch && sender_state->tlbEntry)
            pagingProtectionChecks(tc, pkt, local_entry, mode);
 
        int page_size = local_entry->size();
        Addr paddr = local_entry->paddr | (vaddr & (page_size - 1));
        DPRINTF(GPUTLB, "Translated %#x -> %#x.\n", vaddr, paddr);
 
        pkt->req->setPaddr(paddr);
 
        if (local_entry->uncacheable)
             pkt->req->setFlags(Request::UNCACHEABLE);
    }
 
    // This is used for atomic translations. Need to
    // make it all happen during the same cycle.
    void
    GpuTLB::CpuSidePort::recvFunctional(PacketPtr pkt)
    {
        GpuTranslationState *sender_state =
            safe_cast<GpuTranslationState*>(pkt->senderState);
 
        ThreadContext *tc = sender_state->tc;
        bool update_stats = !sender_state->isPrefetch;
 
        Addr virt_page_addr = roundDown(pkt->req->getVaddr(),
                                        X86ISA::PageBytes);
 
        if (update_stats)
            tlb->updatePageFootprint(virt_page_addr);
 
        // do the TLB lookup without updating the stats
        bool success = tlb->tlbLookup(pkt->req, tc, update_stats);
        tlbOutcome tlb_outcome = success ? TLB_HIT : TLB_MISS;
 
        // functional mode means no coalescing
        // global metrics are the same as the local metrics
        if (update_stats) {
            tlb->stats.globalNumTLBAccesses++;
 
            if (success) {
                sender_state->hitLevel = sender_state->reqCnt.size();
                tlb->stats.globalNumTLBHits++;
            }
        }
 
        if (!success) {
            if (update_stats)
                tlb->stats.globalNumTLBMisses++;
            if (tlb->hasMemSidePort) {
                // there is a TLB below -> propagate down the TLB hierarchy
                tlb->memSidePort[0]->sendFunctional(pkt);
                // If no valid translation from a prefetch, then just return
                if (sender_state->isPrefetch && !pkt->req->hasPaddr())
                    return;
            } else {
                // Need to access the page table and update the TLB
                DPRINTF(GPUTLB, "Doing a page walk for address %#x\n",
                        virt_page_addr);
 
                Process *p = tc->getProcessPtr();
 
                Addr vaddr = pkt->req->getVaddr();
 
                Addr alignedVaddr = p->pTable->pageAlign(vaddr);
                assert(alignedVaddr == virt_page_addr);
 
                const EmulationPageTable::Entry *pte =
                        p->pTable->lookup(vaddr);
                if (!pte && sender_state->tlbMode != BaseMMU::Execute &&
                        p->fixupFault(vaddr)) {
                    pte = p->pTable->lookup(vaddr);
                }
 
                if (!sender_state->isPrefetch) {
                    // no PageFaults are permitted after
                    // the second page table lookup
                    assert(pte);
 
                    DPRINTF(GPUTLB, "Mapping %#x to %#x\n", alignedVaddr,
                            pte->paddr);
 
                    sender_state->tlbEntry =
                        new TlbEntry(p->pid(), virt_page_addr,
                                     pte->paddr, false, false);
                } else {
                    // If this was a prefetch, then do the normal thing if it
                    // was a successful translation.  Otherwise, send an empty
                    // TLB entry back so that it can be figured out as empty
                    // and handled accordingly.
                    if (pte) {
                        DPRINTF(GPUTLB, "Mapping %#x to %#x\n", alignedVaddr,
                                pte->paddr);
 
                        sender_state->tlbEntry =
                            new TlbEntry(p->pid(), virt_page_addr,
                                         pte->paddr, false, false);
                    } else {
                        DPRINTF(GPUPrefetch, "Prefetch failed %#x\n",
                                alignedVaddr);
 
                        sender_state->tlbEntry = nullptr;
 
                        return;
                    }
                }
            }
        } else {
            DPRINTF(GPUPrefetch, "Functional Hit for vaddr %#x\n",
                    tlb->lookup(pkt->req->getVaddr()));
 
            TlbEntry *entry = tlb->lookup(pkt->req->getVaddr(),
                                             update_stats);
 
            assert(entry);
 
            auto p = sender_state->tc->getProcessPtr();
            sender_state->tlbEntry =
                new TlbEntry(p->pid(), entry->vaddr, entry->paddr,
                             false, false);
        }
        // This is the function that would populate pkt->req with the paddr of
        // the translation. But if no translation happens (i.e Prefetch fails)
        // then the early returns in the above code wiill keep this function
        // from executing.
        tlb->handleFuncTranslationReturn(pkt, tlb_outcome);
    }
 
    void
    GpuTLB::CpuSidePort::recvReqRetry()
    {
        // The CPUSidePort never sends anything but replies. No retries
        // expected.
        panic("recvReqRetry called");
    }
 
    AddrRangeList
    GpuTLB::CpuSidePort::getAddrRanges() const
    {
        // currently not checked by the requestor
        AddrRangeList ranges;
 
        return ranges;
    }
 
    bool
    GpuTLB::MemSidePort::recvTimingResp(PacketPtr pkt)
    {
        Addr virt_page_addr = roundDown(pkt->req->getVaddr(),
                                        X86ISA::PageBytes);
 
        DPRINTF(GPUTLB, "MemSidePort recvTiming for virt_page_addr %#x\n",
                virt_page_addr);
 
        TLBEvent *tlb_event = tlb->translationReturnEvent[virt_page_addr];
        assert(tlb_event);
        assert(virt_page_addr == tlb_event->getTLBEventVaddr());
 
        tlb_event->updateOutcome(MISS_RETURN);
        tlb->schedule(tlb_event, curTick()+tlb->clockPeriod());
 
        return true;
    }
 
    void
    GpuTLB::MemSidePort::recvReqRetry()
    {
        // No retries should reach the TLB. The retries
        // should only reach the TLBCoalescer.
        panic("recvReqRetry called");
    }
 
    void
    GpuTLB::cleanup()
    {
        while (!cleanupQueue.empty()) {
            Addr cleanup_addr = cleanupQueue.front();
            cleanupQueue.pop();
 
            // delete TLBEvent
            TLBEvent * old_tlb_event = translationReturnEvent[cleanup_addr];
            delete old_tlb_event;
            translationReturnEvent.erase(cleanup_addr);
 
            // update number of outstanding requests
            outstandingReqs--;
        }
 
        for (int i = 0; i < cpuSidePort.size(); ++i) {
            cpuSidePort[i]->sendRetryReq();
        }
    }
 
    void
    GpuTLB::updatePageFootprint(Addr virt_page_addr)
    {
 
        std::pair<AccessPatternTable::iterator, bool> ret;
 
        AccessInfo tmp_access_info;
        tmp_access_info.lastTimeAccessed = 0;
        tmp_access_info.accessesPerPage = 0;
        tmp_access_info.totalReuseDistance = 0;
        tmp_access_info.sumDistance = 0;
        tmp_access_info.meanDistance = 0;
 
        ret = TLBFootprint.insert(
            AccessPatternTable::value_type(virt_page_addr, tmp_access_info));
 
        bool first_page_access = ret.second;
 
        if (first_page_access) {
            stats.numUniquePages++;
        } else  {
            int accessed_before;
            accessed_before  = curTick() - ret.first->second.lastTimeAccessed;
            ret.first->second.totalReuseDistance += accessed_before;
        }
 
        ret.first->second.accessesPerPage++;
        ret.first->second.lastTimeAccessed = curTick();
 
        if (accessDistance) {
            ret.first->second.localTLBAccesses
                .push_back(stats.localNumTLBAccesses.value());
        }
    }
 
    void
    GpuTLB::exitCallback()
    {
        std::ostream *page_stat_file = nullptr;
 
        if (accessDistance) {
 
            // print per page statistics to a separate file (.csv format)
            // simout is the gem5 output directory (default is m5out or the one
            // specified with -d
            page_stat_file = simout.create(name().c_str())->stream();
 
            // print header
            *page_stat_file
                << "page,max_access_distance,mean_access_distance, "
                << "stddev_distance" << std::endl;
        }
 
        // update avg. reuse distance footprint
        unsigned int sum_avg_reuse_distance_per_page = 0;
 
        // iterate through all pages seen by this TLB
        for (auto &iter : TLBFootprint) {
            sum_avg_reuse_distance_per_page += iter.second.totalReuseDistance /
                                               iter.second.accessesPerPage;
 
            if (accessDistance) {
                unsigned int tmp = iter.second.localTLBAccesses[0];
                unsigned int prev = tmp;
 
                for (int i = 0; i < iter.second.localTLBAccesses.size(); ++i) {
                    if (i) {
                        tmp = prev + 1;
                    }
 
                    prev = iter.second.localTLBAccesses[i];
                    // update the localTLBAccesses value
                    // with the actual differece
                    iter.second.localTLBAccesses[i] -= tmp;
                    // compute the sum of AccessDistance per page
                    // used later for mean
                    iter.second.sumDistance +=
                        iter.second.localTLBAccesses[i];
                }
 
                iter.second.meanDistance =
                    iter.second.sumDistance / iter.second.accessesPerPage;
 
                // compute std_dev and max  (we need a second round because we
                // need to know the mean value
                unsigned int max_distance = 0;
                unsigned int stddev_distance = 0;
 
                for (int i = 0; i < iter.second.localTLBAccesses.size(); ++i) {
                    unsigned int tmp_access_distance =
                        iter.second.localTLBAccesses[i];
 
                    if (tmp_access_distance > max_distance) {
                        max_distance = tmp_access_distance;
                    }
 
                    unsigned int diff =
                        tmp_access_distance - iter.second.meanDistance;
                    stddev_distance += pow(diff, 2);
 
                }
 
                stddev_distance =
                    sqrt(stddev_distance/iter.second.accessesPerPage);
 
                if (page_stat_file) {
                    *page_stat_file << std::hex << iter.first << ",";
                    *page_stat_file << std::dec << max_distance << ",";
                    *page_stat_file << std::dec << iter.second.meanDistance
                                    << ",";
                    *page_stat_file << std::dec << stddev_distance;
                    *page_stat_file << std::endl;
                }
 
                // erase the localTLBAccesses array
                iter.second.localTLBAccesses.clear();
            }
        }
 
        if (!TLBFootprint.empty()) {
            stats.avgReuseDistance =
                sum_avg_reuse_distance_per_page / TLBFootprint.size();
        }
 
        //clear the TLBFootprint map
        TLBFootprint.clear();
    }
 
    GpuTLB::GpuTLBStats::GpuTLBStats(statistics::Group *parent)
        : statistics::Group(parent),
          ADD_STAT(localNumTLBAccesses, "Number of TLB accesses"),
          ADD_STAT(localNumTLBHits, "Number of TLB hits"),
          ADD_STAT(localNumTLBMisses, "Number of TLB misses"),
          ADD_STAT(localTLBMissRate, "TLB miss rate"),
          ADD_STAT(globalNumTLBAccesses, "Number of TLB accesses"),
          ADD_STAT(globalNumTLBHits, "Number of TLB hits"),
          ADD_STAT(globalNumTLBMisses, "Number of TLB misses"),
          ADD_STAT(globalTLBMissRate, "TLB miss rate"),
          ADD_STAT(accessCycles, "Cycles spent accessing this TLB level"),
          ADD_STAT(pageTableCycles, "Cycles spent accessing the page table"),
          ADD_STAT(numUniquePages, "Number of unique pages touched"),
          ADD_STAT(localCycles, "Number of cycles spent in queue for all "
                   "incoming reqs"),
          ADD_STAT(localLatency, "Avg. latency over incoming coalesced reqs"),
          ADD_STAT(avgReuseDistance, "avg. reuse distance over all pages (in "
                   "ticks)")
    {
        localLatency = localCycles / localNumTLBAccesses;
 
        localTLBMissRate = 100 * localNumTLBMisses / localNumTLBAccesses;
        globalTLBMissRate = 100 * globalNumTLBMisses / globalNumTLBAccesses;
    }
} // namespace X86ISA
} // namespace gem5