src/sim/mem_state.cc - public/gem5 - Git at Google

 /*
  * Copyright (c) 2017-2020 Advanced Micro Devices, Inc.
  * All rights reserved.
  *
  * 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.
  */

 #include "sim/mem_state.hh"

 #include <cassert>

 #include "arch/generic/mmu.hh"
 #include "debug/Vma.hh"
 #include "mem/se_translating_port_proxy.hh"
 #include "sim/process.hh"
 #include "sim/syscall_debug_macros.hh"
 #include "sim/system.hh"
 #include "sim/vma.hh"

 namespace gem5
 {

 MemState::MemState(Process *owner, Addr brk_point, Addr stack_base,
                    Addr max_stack_size, Addr next_thread_stack_base,
                    Addr mmap_end)
     : _ownerProcess(owner),
       _pageBytes(owner->pTable->pageSize()), _brkPoint(brk_point),
       _stackBase(stack_base), _stackSize(max_stack_size),
       _maxStackSize(max_stack_size), _stackMin(stack_base - max_stack_size),
       _nextThreadStackBase(next_thread_stack_base),
       _mmapEnd(mmap_end), _endBrkPoint(brk_point)
 {
 }

 MemState&
 MemState::operator=(const MemState &in)
 {
     if (this == &in)
         return *this;

     _pageBytes = in._pageBytes;
     _brkPoint = in._brkPoint;
     _stackBase = in._stackBase;
     _stackSize = in._stackSize;
     _maxStackSize = in._maxStackSize;
     _stackMin = in._stackMin;
     _nextThreadStackBase = in._nextThreadStackBase;
     _mmapEnd = in._mmapEnd;
     _endBrkPoint = in._endBrkPoint;
     _vmaList = in._vmaList; /* This assignment does a deep copy. */

     return *this;
 }

 void
 MemState::resetOwner(Process *owner)
 {
     _ownerProcess = owner;
 }

 bool
 MemState::isUnmapped(Addr start_addr, Addr length)
 {
     Addr end_addr = start_addr + length;
     const AddrRange range(start_addr, end_addr);
     for (const auto &vma : _vmaList) {
         if (vma.intersects(range))
             return false;
     }

     /**
      * In case someone skips the VMA interface and just directly maps memory
      * also consult the page tables to make sure that this memory isnt mapped.
      */
     for (auto start = start_addr; start < end_addr;
          start += _pageBytes) {
         if (_ownerProcess->pTable->lookup(start) != nullptr) {
             panic("Someone allocated physical memory at VA %p without "
                   "creating a VMA!\n", start);
             return false;
         }
     }
     return true;
 }

 void
 MemState::updateBrkRegion(Addr old_brk, Addr new_brk)
 {
     /**
      * To make this simple, avoid reducing the heap memory area if the
      * new_brk point is less than the old_brk; this occurs when the heap is
      * receding because the application has given back memory. The brk point
      * is still tracked in the MemState class as an independent field so that
      * it can be returned to the application; we just do not update the
      * region unless we expand it out.
      */
     if (new_brk < old_brk) {
         _brkPoint = new_brk;
         return;
     }

     /**
      * The regions must be page aligned but the break point can be set on
      * byte boundaries. Ensure that the restriction is maintained here by
      * extending the request out to the end of the page. (The roundUp
      * function will not round up an already aligned page.)
      */
     auto page_aligned_brk = roundUp(new_brk, _pageBytes);

     /**
      * Create a new mapping for the heap region. We only create a mapping
      * for the extra memory that is requested so we do not create a situation
      * where there can be overlapping mappings in the regions.
      *
      * Since we do not track the type of the region and we also do not
      * coalesce the regions together, we can create a fragmented set of
      * heap regions. To resolve this, we keep the furthest point ever mapped
      * by the _endBrkPoint field.
      */
     if (page_aligned_brk > _endBrkPoint) {
         auto length = page_aligned_brk - _endBrkPoint;
         /**
          * Check if existing mappings impede the expansion of brk expansion.
          * If brk cannot expand, it must return the original, unmodified brk
          * address and should not modify the mappings here.
          */
         if (!isUnmapped(_endBrkPoint, length)) {
             return;
         }

         /**
          * Note that the heap regions are always contiguous but there is
          * no mechanism right now to coalesce together memory that belongs
          * to the same region with similar access permissions. This could be
          * implemented if it actually becomes necessary; probably only
          * necessary if the list becomes too long to walk.
          */
         mapRegion(_endBrkPoint, length, "heap");
         _endBrkPoint = page_aligned_brk;
     }

     _brkPoint = new_brk;
 }

 void
 MemState::mapRegion(Addr start_addr, Addr length,
                     const std::string& region_name, int sim_fd, Addr offset)
 {
     DPRINTF(Vma, "memstate: creating vma (%s) [0x%x - 0x%x]\n",
             region_name.c_str(), start_addr, start_addr + length);

     /**
      * Avoid creating a region that has preexisting mappings. This should
      * not happen under normal circumstances so consider this to be a bug.
      */
     assert(isUnmapped(start_addr, length));

     /**
      * Record the region in our list structure.
      */
     _vmaList.emplace_back(AddrRange(start_addr, start_addr + length),
                           _pageBytes, region_name, sim_fd, offset);
 }

 void
 MemState::unmapRegion(Addr start_addr, Addr length)
 {
     Addr end_addr = start_addr + length;
     const AddrRange range(start_addr, end_addr);

     auto vma = std::begin(_vmaList);
     while (vma != std::end(_vmaList)) {
         if (vma->isStrictSuperset(range)) {
             DPRINTF(Vma, "memstate: split vma [0x%x - 0x%x] into "
                     "[0x%x - 0x%x] and [0x%x - 0x%x]\n",
                     vma->start(), vma->end(),
                     vma->start(), start_addr,
                     end_addr, vma->end());
             /**
              * Need to split into two smaller regions.
              * Create a clone of the old VMA and slice it to the right.
              */
             _vmaList.push_back(*vma);
             _vmaList.back().sliceRegionRight(start_addr);

             /**
              * Slice old VMA to encapsulate the left region.
              */
             vma->sliceRegionLeft(end_addr);

             /**
              * Region cannot be in any more VMA, because it is completely
              * contained in this one!
              */
             break;
         } else if (vma->isSubset(range)) {
             DPRINTF(Vma, "memstate: destroying vma [0x%x - 0x%x]\n",
                     vma->start(), vma->end());
             /**
              * Need to nuke the existing VMA.
              */
             vma = _vmaList.erase(vma);

             continue;

         } else if (vma->intersects(range)) {
             /**
              * Trim up the existing VMA.
              */
             if (vma->start() < start_addr) {
                 DPRINTF(Vma, "memstate: resizing vma [0x%x - 0x%x] "
                         "into [0x%x - 0x%x]\n",
                         vma->start(), vma->end(),
                         vma->start(), start_addr);
                 /**
                  * Overlaps from the right.
                  */
                 vma->sliceRegionRight(start_addr);
             } else {
                 DPRINTF(Vma, "memstate: resizing vma [0x%x - 0x%x] "
                         "into [0x%x - 0x%x]\n",
                         vma->start(), vma->end(),
                         end_addr, vma->end());
                 /**
                  * Overlaps from the left.
                  */
                 vma->sliceRegionLeft(end_addr);
             }
         }

         vma++;
     }

     /**
      * TLBs need to be flushed to remove any stale mappings from regions
      * which were unmapped. Currently the entire TLB is flushed. This results
      * in functionally correct execution, but real systems do not flush all
      * entries when a single mapping changes since it degrades performance.
      * There is currently no general method across all TLB implementations
      * that can flush just part of the address space.
      */
     for (auto *tc: _ownerProcess->system->threads) {
         tc->getMMUPtr()->flushAll();
     }

     do {
         if (!_ownerProcess->pTable->isUnmapped(start_addr, _pageBytes))
             _ownerProcess->pTable->unmap(start_addr, _pageBytes);

         start_addr += _pageBytes;

         /**
          * The regions need to always be page-aligned otherwise the while
          * condition will loop indefinitely. (The Addr type is currently
          * defined to be uint64_t in src/base/types.hh; it can underflow
          * since it is unsigned.)
          */
         length -= _pageBytes;
     } while (length > 0);
 }

 void
 MemState::remapRegion(Addr start_addr, Addr new_start_addr, Addr length)
 {
     Addr end_addr = start_addr + length;
     const AddrRange range(start_addr, end_addr);

     auto vma = std::begin(_vmaList);
     while (vma != std::end(_vmaList)) {
         if (vma->isStrictSuperset(range)) {
             /**
              * Create clone of the old VMA and slice right.
              */
             _vmaList.push_back(*vma);
             _vmaList.back().sliceRegionRight(start_addr);

             /**
              * Create clone of the old VMA and slice it left.
              */
             _vmaList.push_back(*vma);
             _vmaList.back().sliceRegionLeft(end_addr);

             /**
              * Slice the old VMA left and right to adjust the file backing,
              * then overwrite the virtual addresses!
              */
             vma->sliceRegionLeft(start_addr);
             vma->sliceRegionRight(end_addr);
             vma->remap(new_start_addr);

             /**
              * The region cannot be in any more VMAs, because it is
              * completely contained in this one!
              */
             break;
         } else if (vma->isSubset(range)) {
             /**
              * Just go ahead and remap it!
              */
             vma->remap(vma->start() - start_addr + new_start_addr);
         } else if (vma->intersects(range)) {
             /**
              * Create a clone of the old VMA.
              */
             _vmaList.push_back(*vma);

             if (vma->start() < start_addr) {
                 /**
                  * Overlaps from the right.
                  */
                 _vmaList.back().sliceRegionRight(start_addr);

                 /**
                  * Remap the old region.
                  */
                 vma->sliceRegionLeft(start_addr);
                 vma->remap(new_start_addr);
             } else {
                 /**
                  * Overlaps from the left.
                  */
                 _vmaList.back().sliceRegionLeft(end_addr);

                 /**
                  * Remap the old region.
                  */
                 vma->sliceRegionRight(end_addr);
                 vma->remap(new_start_addr + vma->start() - start_addr);
             }
         }

         vma++;
     }

     /**
      * TLBs need to be flushed to remove any stale mappings from regions
      * which were remapped. Currently the entire TLB is flushed. This results
      * in functionally correct execution, but real systems do not flush all
      * entries when a single mapping changes since it degrades performance.
      * There is currently no general method across all TLB implementations
      * that can flush just part of the address space.
      */
     for (auto *tc: _ownerProcess->system->threads) {
         tc->getMMUPtr()->flushAll();
     }

     do {
         if (!_ownerProcess->pTable->isUnmapped(start_addr, _pageBytes))
             _ownerProcess->pTable->remap(start_addr, _pageBytes,
                                          new_start_addr);

         start_addr += _pageBytes;
         new_start_addr += _pageBytes;

         /**
          * The regions need to always be page-aligned otherwise the while
          * condition will loop indefinitely. (The Addr type is currently
          * defined to be uint64_t in src/base/types.hh; it can underflow
          * since it is unsigned.)
          */
         length -= _pageBytes;
     } while (length > 0);
 }

 bool
 MemState::fixupFault(Addr vaddr)
 {
     /**
      * Check if we are accessing a mapped virtual address. If so then we
      * just haven't allocated it a physical page yet and can do so here.
      */
     for (const auto &vma : _vmaList) {
         if (vma.contains(vaddr)) {
             Addr vpage_start = roundDown(vaddr, _pageBytes);
             _ownerProcess->allocateMem(vpage_start, _pageBytes);

             /**
              * We are assuming that fresh pages are zero-filled, so there is
              * no need to zero them out when there is no backing file.
              * This assumption will not hold true if/when physical pages
              * are recycled.
              */
             if (vma.hasHostBuf()) {
                 /**
                  * Write the memory for the host buffer contents for all
                  * ThreadContexts associated with this process.
                  */
                 for (auto &cid : _ownerProcess->contextIds) {
                     auto *tc = _ownerProcess->system->threads[cid];
                     SETranslatingPortProxy
                         virt_mem(tc, SETranslatingPortProxy::Always);
                     vma.fillMemPages(vpage_start, _pageBytes, virt_mem);
                 }
             }
             return true;
         }
     }

     /**
      * Check if the stack needs to be grown in the case where the ISAs
      * process argsInit does not explicitly map the entire stack.
      *
      * Check if this is already on the stack and there's just no page there
      * yet.
      */
     if (vaddr >= _stackMin && vaddr < _stackBase) {
         _ownerProcess->allocateMem(roundDown(vaddr, _pageBytes), _pageBytes);
         return true;
     }

     /**
      * We've accessed the next page of the stack, so extend it to include
      * this address.
      */
     if (vaddr < _stackMin && vaddr >= _stackBase - _maxStackSize) {
         while (vaddr < _stackMin) {
             _stackMin -= _pageBytes;
             if (_stackBase - _stackMin > _maxStackSize) {
                 fatal("Maximum stack size exceeded\n");
             }
             _ownerProcess->allocateMem(_stackMin, _pageBytes);
             inform("Increasing stack size by one page.");
         }
         return true;
     }

     return false;
 }

 Addr
 MemState::extendMmap(Addr length)
 {
     Addr start = _mmapEnd;

     if (_ownerProcess->mmapGrowsDown())
         start = _mmapEnd - length;

     // Look for a contiguous region of free virtual memory.  We can't assume
     // that the region beyond mmap_end is free because of fixed mappings from
     // the user.
     while (!isUnmapped(start, length)) {
         DPRINTF(Vma, "memstate: cannot extend vma for mmap region at %p. "
                 "Virtual address range is already reserved! Skipping a page "
                 "and trying again!\n", start);
         start = (_ownerProcess->mmapGrowsDown()) ? start - _pageBytes :
             start + _pageBytes;
     }

     DPRINTF(Vma, "memstate: extending mmap region (old %p) (new %p)\n",
             _mmapEnd,
             _ownerProcess->mmapGrowsDown() ? start : start + length);

     _mmapEnd = _ownerProcess->mmapGrowsDown() ? start : start + length;

     return start;
 }

 std::string
 MemState::printVmaList()
 {
     std::stringstream file_content;

     for (auto vma : _vmaList) {
         std::stringstream line;
         line << std::hex << vma.start() << "-";
         line << std::hex << vma.end() << " ";
         line << "r-xp 00000000 00:00 0 ";
         line << "[" << vma.getName() << "]" << std::endl;
         file_content << line.str();
     }

     return file_content.str();
 }

 } // namespace gem5
	/*
	* Copyright (c) 2017-2020 Advanced Micro Devices, Inc.
	* All rights reserved.
	*
	* 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.
	*/

	#include "sim/mem_state.hh"

	#include <cassert>

	#include "arch/generic/mmu.hh"
	#include "debug/Vma.hh"
	#include "mem/se_translating_port_proxy.hh"
	#include "sim/process.hh"
	#include "sim/syscall_debug_macros.hh"
	#include "sim/system.hh"
	#include "sim/vma.hh"

	namespace gem5
	{

	MemState::MemState(Process *owner, Addr brk_point, Addr stack_base,
	Addr max_stack_size, Addr next_thread_stack_base,
	Addr mmap_end)
	: _ownerProcess(owner),
	_pageBytes(owner->pTable->pageSize()), _brkPoint(brk_point),
	_stackBase(stack_base), _stackSize(max_stack_size),
	_maxStackSize(max_stack_size), _stackMin(stack_base - max_stack_size),
	_nextThreadStackBase(next_thread_stack_base),
	_mmapEnd(mmap_end), _endBrkPoint(brk_point)
	{
	}

	MemState&
	MemState::operator=(const MemState &in)
	{
	if (this == &in)
	return *this;

	_pageBytes = in._pageBytes;
	_brkPoint = in._brkPoint;
	_stackBase = in._stackBase;
	_stackSize = in._stackSize;
	_maxStackSize = in._maxStackSize;
	_stackMin = in._stackMin;
	_nextThreadStackBase = in._nextThreadStackBase;
	_mmapEnd = in._mmapEnd;
	_endBrkPoint = in._endBrkPoint;
	_vmaList = in._vmaList; /* This assignment does a deep copy. */

	return *this;
	}

	void
	MemState::resetOwner(Process *owner)
	{
	_ownerProcess = owner;
	}

	bool
	MemState::isUnmapped(Addr start_addr, Addr length)
	{
	Addr end_addr = start_addr + length;
	const AddrRange range(start_addr, end_addr);
	for (const auto &vma : _vmaList) {
	if (vma.intersects(range))
	return false;
	}

	/**
	* In case someone skips the VMA interface and just directly maps memory
	* also consult the page tables to make sure that this memory isnt mapped.
	*/
	for (auto start = start_addr; start < end_addr;
	start += _pageBytes) {
	if (_ownerProcess->pTable->lookup(start) != nullptr) {
	panic("Someone allocated physical memory at VA %p without "
	"creating a VMA!\n", start);
	return false;
	}
	}
	return true;
	}

	void
	MemState::updateBrkRegion(Addr old_brk, Addr new_brk)
	{
	/**
	* To make this simple, avoid reducing the heap memory area if the
	* new_brk point is less than the old_brk; this occurs when the heap is
	* receding because the application has given back memory. The brk point
	* is still tracked in the MemState class as an independent field so that
	* it can be returned to the application; we just do not update the
	* region unless we expand it out.
	*/
	if (new_brk < old_brk) {
	_brkPoint = new_brk;
	return;
	}

	/**
	* The regions must be page aligned but the break point can be set on
	* byte boundaries. Ensure that the restriction is maintained here by
	* extending the request out to the end of the page. (The roundUp
	* function will not round up an already aligned page.)
	*/
	auto page_aligned_brk = roundUp(new_brk, _pageBytes);

	/**
	* Create a new mapping for the heap region. We only create a mapping
	* for the extra memory that is requested so we do not create a situation
	* where there can be overlapping mappings in the regions.
	*
	* Since we do not track the type of the region and we also do not
	* coalesce the regions together, we can create a fragmented set of
	* heap regions. To resolve this, we keep the furthest point ever mapped
	* by the _endBrkPoint field.
	*/
	if (page_aligned_brk > _endBrkPoint) {
	auto length = page_aligned_brk - _endBrkPoint;
	/**
	* Check if existing mappings impede the expansion of brk expansion.
	* If brk cannot expand, it must return the original, unmodified brk
	* address and should not modify the mappings here.
	*/
	if (!isUnmapped(_endBrkPoint, length)) {
	return;
	}

	/**
	* Note that the heap regions are always contiguous but there is
	* no mechanism right now to coalesce together memory that belongs
	* to the same region with similar access permissions. This could be
	* implemented if it actually becomes necessary; probably only
	* necessary if the list becomes too long to walk.
	*/
	mapRegion(_endBrkPoint, length, "heap");
	_endBrkPoint = page_aligned_brk;
	}

	_brkPoint = new_brk;
	}

	void
	MemState::mapRegion(Addr start_addr, Addr length,
	const std::string& region_name, int sim_fd, Addr offset)
	{
	DPRINTF(Vma, "memstate: creating vma (%s) [0x%x - 0x%x]\n",
	region_name.c_str(), start_addr, start_addr + length);

	/**
	* Avoid creating a region that has preexisting mappings. This should
	* not happen under normal circumstances so consider this to be a bug.
	*/
	assert(isUnmapped(start_addr, length));

	/**
	* Record the region in our list structure.
	*/
	_vmaList.emplace_back(AddrRange(start_addr, start_addr + length),
	_pageBytes, region_name, sim_fd, offset);
	}

	void
	MemState::unmapRegion(Addr start_addr, Addr length)
	{
	Addr end_addr = start_addr + length;
	const AddrRange range(start_addr, end_addr);

	auto vma = std::begin(_vmaList);
	while (vma != std::end(_vmaList)) {
	if (vma->isStrictSuperset(range)) {
	DPRINTF(Vma, "memstate: split vma [0x%x - 0x%x] into "
	"[0x%x - 0x%x] and [0x%x - 0x%x]\n",
	vma->start(), vma->end(),
	vma->start(), start_addr,
	end_addr, vma->end());
	/**
	* Need to split into two smaller regions.
	* Create a clone of the old VMA and slice it to the right.
	*/
	_vmaList.push_back(*vma);
	_vmaList.back().sliceRegionRight(start_addr);

	/**
	* Slice old VMA to encapsulate the left region.
	*/
	vma->sliceRegionLeft(end_addr);

	/**
	* Region cannot be in any more VMA, because it is completely
	* contained in this one!
	*/
	break;
	} else if (vma->isSubset(range)) {
	DPRINTF(Vma, "memstate: destroying vma [0x%x - 0x%x]\n",
	vma->start(), vma->end());
	/**
	* Need to nuke the existing VMA.
	*/
	vma = _vmaList.erase(vma);

	continue;

	} else if (vma->intersects(range)) {
	/**
	* Trim up the existing VMA.
	*/
	if (vma->start() < start_addr) {
	DPRINTF(Vma, "memstate: resizing vma [0x%x - 0x%x] "
	"into [0x%x - 0x%x]\n",
	vma->start(), vma->end(),
	vma->start(), start_addr);
	/**
	* Overlaps from the right.
	*/
	vma->sliceRegionRight(start_addr);
	} else {
	DPRINTF(Vma, "memstate: resizing vma [0x%x - 0x%x] "
	"into [0x%x - 0x%x]\n",
	vma->start(), vma->end(),
	end_addr, vma->end());
	/**
	* Overlaps from the left.
	*/
	vma->sliceRegionLeft(end_addr);
	}
	}

	vma++;
	}

	/**
	* TLBs need to be flushed to remove any stale mappings from regions
	* which were unmapped. Currently the entire TLB is flushed. This results
	* in functionally correct execution, but real systems do not flush all
	* entries when a single mapping changes since it degrades performance.
	* There is currently no general method across all TLB implementations
	* that can flush just part of the address space.
	*/
	for (auto *tc: _ownerProcess->system->threads) {
	tc->getMMUPtr()->flushAll();
	}

	do {
	if (!_ownerProcess->pTable->isUnmapped(start_addr, _pageBytes))
	_ownerProcess->pTable->unmap(start_addr, _pageBytes);

	start_addr += _pageBytes;

	/**
	* The regions need to always be page-aligned otherwise the while
	* condition will loop indefinitely. (The Addr type is currently
	* defined to be uint64_t in src/base/types.hh; it can underflow
	* since it is unsigned.)
	*/
	length -= _pageBytes;
	} while (length > 0);
	}

	void
	MemState::remapRegion(Addr start_addr, Addr new_start_addr, Addr length)
	{
	Addr end_addr = start_addr + length;
	const AddrRange range(start_addr, end_addr);

	auto vma = std::begin(_vmaList);
	while (vma != std::end(_vmaList)) {
	if (vma->isStrictSuperset(range)) {
	/**
	* Create clone of the old VMA and slice right.
	*/
	_vmaList.push_back(*vma);
	_vmaList.back().sliceRegionRight(start_addr);

	/**
	* Create clone of the old VMA and slice it left.
	*/
	_vmaList.push_back(*vma);
	_vmaList.back().sliceRegionLeft(end_addr);

	/**
	* Slice the old VMA left and right to adjust the file backing,
	* then overwrite the virtual addresses!
	*/
	vma->sliceRegionLeft(start_addr);
	vma->sliceRegionRight(end_addr);
	vma->remap(new_start_addr);

	/**
	* The region cannot be in any more VMAs, because it is
	* completely contained in this one!
	*/
	break;
	} else if (vma->isSubset(range)) {
	/**
	* Just go ahead and remap it!
	*/
	vma->remap(vma->start() - start_addr + new_start_addr);
	} else if (vma->intersects(range)) {
	/**
	* Create a clone of the old VMA.
	*/
	_vmaList.push_back(*vma);

	if (vma->start() < start_addr) {
	/**
	* Overlaps from the right.
	*/
	_vmaList.back().sliceRegionRight(start_addr);

	/**
	* Remap the old region.
	*/
	vma->sliceRegionLeft(start_addr);
	vma->remap(new_start_addr);
	} else {
	/**
	* Overlaps from the left.
	*/
	_vmaList.back().sliceRegionLeft(end_addr);

	/**
	* Remap the old region.
	*/
	vma->sliceRegionRight(end_addr);
	vma->remap(new_start_addr + vma->start() - start_addr);
	}
	}

	vma++;
	}

	/**
	* TLBs need to be flushed to remove any stale mappings from regions
	* which were remapped. Currently the entire TLB is flushed. This results
	* in functionally correct execution, but real systems do not flush all
	* entries when a single mapping changes since it degrades performance.
	* There is currently no general method across all TLB implementations
	* that can flush just part of the address space.
	*/
	for (auto *tc: _ownerProcess->system->threads) {
	tc->getMMUPtr()->flushAll();
	}

	do {
	if (!_ownerProcess->pTable->isUnmapped(start_addr, _pageBytes))
	_ownerProcess->pTable->remap(start_addr, _pageBytes,
	new_start_addr);

	start_addr += _pageBytes;
	new_start_addr += _pageBytes;

	/**
	* The regions need to always be page-aligned otherwise the while
	* condition will loop indefinitely. (The Addr type is currently
	* defined to be uint64_t in src/base/types.hh; it can underflow
	* since it is unsigned.)
	*/
	length -= _pageBytes;
	} while (length > 0);
	}

	bool
	MemState::fixupFault(Addr vaddr)
	{
	/**
	* Check if we are accessing a mapped virtual address. If so then we
	* just haven't allocated it a physical page yet and can do so here.
	*/
	for (const auto &vma : _vmaList) {
	if (vma.contains(vaddr)) {
	Addr vpage_start = roundDown(vaddr, _pageBytes);
	_ownerProcess->allocateMem(vpage_start, _pageBytes);

	/**
	* We are assuming that fresh pages are zero-filled, so there is
	* no need to zero them out when there is no backing file.
	* This assumption will not hold true if/when physical pages
	* are recycled.
	*/
	if (vma.hasHostBuf()) {
	/**
	* Write the memory for the host buffer contents for all
	* ThreadContexts associated with this process.
	*/
	for (auto &cid : _ownerProcess->contextIds) {
	auto *tc = _ownerProcess->system->threads[cid];
	SETranslatingPortProxy
	virt_mem(tc, SETranslatingPortProxy::Always);
	vma.fillMemPages(vpage_start, _pageBytes, virt_mem);
	}
	}
	return true;
	}
	}

	/**
	* Check if the stack needs to be grown in the case where the ISAs
	* process argsInit does not explicitly map the entire stack.
	*
	* Check if this is already on the stack and there's just no page there
	* yet.
	*/
	if (vaddr >= _stackMin && vaddr < _stackBase) {
	_ownerProcess->allocateMem(roundDown(vaddr, _pageBytes), _pageBytes);
	return true;
	}

	/**
	* We've accessed the next page of the stack, so extend it to include
	* this address.
	*/
	if (vaddr < _stackMin && vaddr >= _stackBase - _maxStackSize) {
	while (vaddr < _stackMin) {
	_stackMin -= _pageBytes;
	if (_stackBase - _stackMin > _maxStackSize) {
	fatal("Maximum stack size exceeded\n");
	}
	_ownerProcess->allocateMem(_stackMin, _pageBytes);
	inform("Increasing stack size by one page.");
	}
	return true;
	}

	return false;
	}

	Addr
	MemState::extendMmap(Addr length)
	{
	Addr start = _mmapEnd;

	if (_ownerProcess->mmapGrowsDown())
	start = _mmapEnd - length;

	// Look for a contiguous region of free virtual memory. We can't assume
	// that the region beyond mmap_end is free because of fixed mappings from
	// the user.
	while (!isUnmapped(start, length)) {
	DPRINTF(Vma, "memstate: cannot extend vma for mmap region at %p. "
	"Virtual address range is already reserved! Skipping a page "
	"and trying again!\n", start);
	start = (_ownerProcess->mmapGrowsDown()) ? start - _pageBytes :
	start + _pageBytes;
	}

	DPRINTF(Vma, "memstate: extending mmap region (old %p) (new %p)\n",
	_mmapEnd,
	_ownerProcess->mmapGrowsDown() ? start : start + length);

	_mmapEnd = _ownerProcess->mmapGrowsDown() ? start : start + length;

	return start;
	}

	std::string
	MemState::printVmaList()
	{
	std::stringstream file_content;

	for (auto vma : _vmaList) {
	std::stringstream line;
	line << std::hex << vma.start() << "-";
	line << std::hex << vma.end() << " ";
	line << "r-xp 00000000 00:00 0 ";
	line << "[" << vma.getName() << "]" << std::endl;
	file_content << line.str();
	}

	return file_content.str();
	}

	} // namespace gem5