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<li class="toctree-l2 current current-page"><a class="current reference internal" href="#">chapter4练习</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../chapter5/1process.html">与进程有关的重要系统调用</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../chapter5/2core-data-structures.html">进程管理的核心数据结构</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../chapter6/2fs-implementation-1.html">简易文件系统 easy-fs (上)</a></li>
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|
||
<li class="toctree-l2"><a class="reference internal" href="../chapter8/5exercise.html">chapter8 练习</a></li>
|
||
</ul>
|
||
</li>
|
||
</ul>
|
||
<p class="caption" role="heading"><span class="caption-text">附录</span></p>
|
||
<ul>
|
||
<li class="toctree-l1 has-children"><a class="reference internal" href="../appendix-a/index.html">附录 A：Rust 系统编程资料</a><input class="toctree-checkbox" id="toctree-checkbox-17" name="toctree-checkbox-17" role="switch" type="checkbox"/><label for="toctree-checkbox-17"><div class="visually-hidden">Toggle child pages in navigation</div><i class="icon"><svg><use href="#svg-arrow-right"></use></svg></i></label><ul class="simple">
|
||
</ul>
|
||
</li>
|
||
<li class="toctree-l1 has-children"><a class="reference internal" href="../appendix-b/index.html">附录 B：常见工具的使用方法</a><input class="toctree-checkbox" id="toctree-checkbox-18" name="toctree-checkbox-18" role="switch" type="checkbox"/><label for="toctree-checkbox-18"><div class="visually-hidden">Toggle child pages in navigation</div><i class="icon"><svg><use href="#svg-arrow-right"></use></svg></i></label><ul class="simple">
|
||
</ul>
|
||
</li>
|
||
<li class="toctree-l1 has-children"><a class="reference internal" href="../appendix-c/index.html">附录 C：深入机器模式：RustSBI</a><input class="toctree-checkbox" id="toctree-checkbox-19" name="toctree-checkbox-19" role="switch" type="checkbox"/><label for="toctree-checkbox-19"><div class="visually-hidden">Toggle child pages in navigation</div><i class="icon"><svg><use href="#svg-arrow-right"></use></svg></i></label><ul class="simple">
|
||
</ul>
|
||
</li>
|
||
<li class="toctree-l1"><a class="reference internal" href="../appendix-d/index.html">附录 D：RISC-V相关信息</a></li>
|
||
</ul>
|
||
<p class="caption" role="heading"><span class="caption-text">开发注记</span></p>
|
||
<ul>
|
||
<li class="toctree-l1 has-children"><a class="reference internal" href="../setup-sphinx.html">修改和构建本项目</a><input class="toctree-checkbox" id="toctree-checkbox-20" name="toctree-checkbox-20" role="switch" type="checkbox"/><label for="toctree-checkbox-20"><div class="visually-hidden">Toggle child pages in navigation</div><i class="icon"><svg><use href="#svg-arrow-right"></use></svg></i></label><ul class="simple">
|
||
</ul>
|
||
</li>
|
||
<li class="toctree-l1 has-children"><a class="reference internal" href="../rest-example.html">reStructuredText 基本语法</a><input class="toctree-checkbox" id="toctree-checkbox-21" name="toctree-checkbox-21" role="switch" type="checkbox"/><label for="toctree-checkbox-21"><div class="visually-hidden">Toggle child pages in navigation</div><i class="icon"><svg><use href="#svg-arrow-right"></use></svg></i></label><ul class="simple">
|
||
</ul>
|
||
</li>
|
||
</ul>
|
||
|
||
</div>
|
||
</div>
|
||
</div>
|
||
|
||
</div>
|
||
</aside>
|
||
<div class="main">
|
||
<div class="content">
|
||
<article role="main">
|
||
<div class="content-icon-container">
|
||
<div class="theme-toggle-container theme-toggle-content">
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<button class="theme-toggle">
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<div class="visually-hidden">Toggle Light / Dark / Auto color theme</div>
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<svg class="theme-icon-when-auto"><use href="#svg-sun-half"></use></svg>
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<svg class="theme-icon-when-dark"><use href="#svg-moon"></use></svg>
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||
<svg class="theme-icon-when-light"><use href="#svg-sun"></use></svg>
|
||
</button>
|
||
</div>
|
||
<label class="toc-overlay-icon toc-content-icon" for="__toc">
|
||
<div class="visually-hidden">Toggle table of contents sidebar</div>
|
||
<i class="icon"><svg><use href="#svg-toc"></use></svg></i>
|
||
</label>
|
||
</div>
|
||
<div class="section" id="chapter4">
|
||
<h1>chapter4练习<a class="headerlink" href="#chapter4" title="永久链接至标题">¶</a></h1>
|
||
<div class="section" id="lab2">
|
||
<h2>Lab2 编程作业<a class="headerlink" href="#lab2" title="永久链接至标题">¶</a></h2>
|
||
<div class="section" id="sys-get-time-sys-task-info">
|
||
<h3>重写 sys_get_time 和 sys_task_info<a class="headerlink" href="#sys-get-time-sys-task-info" title="永久链接至标题">¶</a></h3>
|
||
<p>引入虚存机制后，原来内核的 sys_get_time 和 sys_task_info 函数实现就无效了。请你重写这个函数，恢复其正常功能。</p>
|
||
</div>
|
||
<div class="section" id="mmap-munmap">
|
||
<h3>mmap 和 munmap 匿名映射<a class="headerlink" href="#mmap-munmap" title="永久链接至标题">¶</a></h3>
|
||
<p><a class="reference external" href="https://man7.org/linux/man-pages/man2/mmap.2.html">mmap</a> 在 Linux 中主要用于在内存中映射文件，
|
||
本次实验简化它的功能，仅用于申请内存。</p>
|
||
<p>请实现 mmap 和 munmap 系统调用，mmap 定义如下：</p>
|
||
<div class="highlight-rust notranslate"><div class="highlight"><pre><span></span><span class="k">fn</span> <span class="nf">sys_mmap</span><span class="p">(</span><span class="n">start</span>: <span class="kt">usize</span><span class="p">,</span><span class="w"> </span><span class="n">len</span>: <span class="kt">usize</span><span class="p">,</span><span class="w"> </span><span class="n">port</span>: <span class="kt">usize</span><span class="p">)</span><span class="w"> </span>-> <span class="kt">isize</span>
|
||
</pre></div>
|
||
</div>
|
||
<ul class="simple">
|
||
<li><p>syscall ID：222</p></li>
|
||
<li><p>申请长度为 len 字节的物理内存（不要求实际物理内存位置，可以随便找一块），将其映射到 start 开始的虚存，内存页属性为 port</p></li>
|
||
<li><dl class="simple">
|
||
<dt>参数：</dt><dd><ul>
|
||
<li><p>start 需要映射的虚存起始地址，要求按页对齐</p></li>
|
||
<li><p>len 映射字节长度，可以为 0</p></li>
|
||
<li><p>port：第 0 位表示是否可读，第 1 位表示是否可写，第 2 位表示是否可执行。其他位无效且必须为 0</p></li>
|
||
</ul>
|
||
</dd>
|
||
</dl>
|
||
</li>
|
||
<li><p>返回值：执行成功则返回 0，错误返回 -1</p></li>
|
||
<li><dl class="simple">
|
||
<dt>说明：</dt><dd><ul>
|
||
<li><p>为了简单，目标虚存区间要求按页对齐，len 可直接按页向上取整，不考虑分配失败时的页回收。</p></li>
|
||
</ul>
|
||
</dd>
|
||
</dl>
|
||
</li>
|
||
<li><dl class="simple">
|
||
<dt>可能的错误：</dt><dd><ul>
|
||
<li><p>start 没有按页大小对齐</p></li>
|
||
<li><p>port & !0x7 != 0 (port 其余位必须为0)</p></li>
|
||
<li><p>port & 0x7 = 0 (这样的内存无意义)</p></li>
|
||
<li><p>[start, start + len) 中存在已经被映射的页</p></li>
|
||
<li><p>物理内存不足</p></li>
|
||
</ul>
|
||
</dd>
|
||
</dl>
|
||
</li>
|
||
</ul>
|
||
<p>munmap 定义如下：</p>
|
||
<div class="highlight-rust notranslate"><div class="highlight"><pre><span></span><span class="k">fn</span> <span class="nf">sys_munmap</span><span class="p">(</span><span class="n">start</span>: <span class="kt">usize</span><span class="p">,</span><span class="w"> </span><span class="n">len</span>: <span class="kt">usize</span><span class="p">)</span><span class="w"> </span>-> <span class="kt">isize</span>
|
||
</pre></div>
|
||
</div>
|
||
<ul class="simple">
|
||
<li><p>syscall ID：215</p></li>
|
||
<li><p>取消到 [start, start + len) 虚存的映射</p></li>
|
||
<li><p>参数和返回值请参考 mmap</p></li>
|
||
<li><dl class="simple">
|
||
<dt>说明：</dt><dd><ul>
|
||
<li><p>为了简单，参数错误时不考虑内存的恢复和回收。</p></li>
|
||
</ul>
|
||
</dd>
|
||
</dl>
|
||
</li>
|
||
<li><dl class="simple">
|
||
<dt>可能的错误：</dt><dd><ul>
|
||
<li><p>[start, start + len) 中存在未被映射的虚存。</p></li>
|
||
</ul>
|
||
</dd>
|
||
</dl>
|
||
</li>
|
||
</ul>
|
||
<p>tips:</p>
|
||
<ul class="simple">
|
||
<li><p>一定要注意 mmap 是的页表项，注意 riscv 页表项的格式与 port 的区别。</p></li>
|
||
<li><p>你增加 PTE_U 了吗？</p></li>
|
||
</ul>
|
||
</div>
|
||
<div class="section" id="id1">
|
||
<h3>实验要求<a class="headerlink" href="#id1" title="永久链接至标题">¶</a></h3>
|
||
<ul class="simple">
|
||
<li><p><a class="reference external" href="https://github.com/LearningOS/rust-based-os-comp2022/tree/main/os4-ref">lab2(os4)参考框架:</a></p></li>
|
||
<li><p>在 <code class="docutils literal notranslate"><span class="pre">os4</span></code> 目录下，实现 mmap 和 munmap 两个系统调用，通过所有测例。</p></li>
|
||
<li><p>报告命名 lab2.md，位于 <code class="docutils literal notranslate"><span class="pre">reports</span></code> 目录下</p></li>
|
||
</ul>
|
||
<p>TIPS：注意 port 参数的语义，它与内核定义的 MapPermission 有明显不同！</p>
|
||
<ul class="simple">
|
||
<li><p>开发并通过所有测例</p></li>
|
||
</ul>
|
||
<p>在 <code class="docutils literal notranslate"><span class="pre">YOUR_LAB2_REPO_DIR</span></code> 下进行编码（可学习参考 <code class="docutils literal notranslate"><span class="pre">os4-ref/src</span></code> 目录下的源代码，并在 <code class="docutils literal notranslate"><span class="pre">os4/src</span></code> 中完成编码），并进行编译测试。</p>
|
||
<div class="admonition note">
|
||
<p class="admonition-title">注解</p>
|
||
<p><strong>测试方式</strong></p>
|
||
<p>你的实现只需且必须通过测例，建议读者感到困惑时先检查测例</p>
|
||
<p>如果实现正确，可在项目仓库的根目录下执行 <code class="docutils literal notranslate"><span class="pre">make</span> <span class="pre">test4</span></code> ，应该看到类似如下的显示输出：</p>
|
||
<div class="highlight-console notranslate"><div class="highlight"><pre><span></span><span class="gp">$ </span><span class="nb">cd</span> YOUR_LAB2_REPO_DIR
|
||
<span class="gp">$ </span>make test4
|
||
<span class="go">......</span>
|
||
<span class="go">[rustsbi] RustSBI version 0.2.2, adapting to RISC-V SBI v1.0.0</span>
|
||
<span class="go">.______ __ __ _______.___________. _______..______ __</span>
|
||
<span class="go">| _ \ | | | | / | | / || _ \ | |</span>
|
||
<span class="go">| |_) | | | | | | (----`---| |----`| (----`| |_) || |</span>
|
||
<span class="go">| / | | | | \ \ | | \ \ | _ < | |</span>
|
||
<span class="go">| |\ \----.| `--' |.----) | | | .----) | | |_) || |</span>
|
||
<span class="go">| _| `._____| \______/ |_______/ |__| |_______/ |______/ |__|</span>
|
||
<span class="go">[rustsbi] Implementation : RustSBI-QEMU Version 0.1.1</span>
|
||
<span class="go">[rustsbi] Platform Name : riscv-virtio,qemu</span>
|
||
<span class="go">[rustsbi] Platform SMP : 1</span>
|
||
<span class="go">[rustsbi] Platform Memory : 0x80000000..0x88000000</span>
|
||
<span class="go">[rustsbi] Boot HART : 0</span>
|
||
<span class="go">[rustsbi] Device Tree Region : 0x87000000..0x87000ef2</span>
|
||
<span class="go">[rustsbi] Firmware Address : 0x80000000</span>
|
||
<span class="go">[rustsbi] Supervisor Address : 0x80200000</span>
|
||
<span class="go">[rustsbi] pmp01: 0x00000000..0x80000000 (-wr)</span>
|
||
<span class="go">[rustsbi] pmp02: 0x80000000..0x80200000 (---)</span>
|
||
<span class="go">[rustsbi] pmp03: 0x80200000..0x88000000 (xwr)</span>
|
||
<span class="go">......</span>
|
||
<span class="go">[PASS] found <Hello, world from user mode program!></span>
|
||
<span class="go">[PASS] found <Test power_3 OK29777!></span>
|
||
<span class="go">[PASS] found <Test power_5 OK29777!></span>
|
||
<span class="go">[PASS] found <Test power_7 OK29777!></span>
|
||
<span class="go">[PASS] found <get_time OK29777! (\d+)></span>
|
||
<span class="go">[PASS] found <Test sleep OK29777!></span>
|
||
<span class="go">[PASS] found <current time_msec = (\d+)></span>
|
||
<span class="go">[PASS] found <time_msec = (\d+) after sleeping (\d+) ticks, delta = (\d+)ms!></span>
|
||
<span class="go">[PASS] found <Test sleep1 passed29777!></span>
|
||
<span class="go">[PASS] found <Test write A OK29777!></span>
|
||
<span class="go">[PASS] found <Test write B OK29777!></span>
|
||
<span class="go">[PASS] found <Test write C OK29777!></span>
|
||
<span class="go">[PASS] found <string from task info test></span>
|
||
<span class="go">[PASS] found <Test task info OK29777!></span>
|
||
<span class="go">[PASS] found <Test 04_1 OK29777!></span>
|
||
<span class="go">[PASS] found <Test 04_4 test OK29777!></span>
|
||
<span class="go">[PASS] found <Test 04_5 ummap OK29777!></span>
|
||
<span class="go">[PASS] found <Test 04_6 ummap2 OK29777!></span>
|
||
<span class="go">[PASS] not found <FAIL: T.T></span>
|
||
<span class="go">[PASS] not found <Should cause error, Test 04_2 fail!></span>
|
||
<span class="go">[PASS] not found <Should cause error, Test 04_3 fail!></span>
|
||
|
||
<span class="go">Test passed29777: 21/21</span>
|
||
<span class="go">Report for lab1 found.</span>
|
||
<span class="go">Report for lab2 found.</span>
|
||
</pre></div>
|
||
</div>
|
||
</div>
|
||
<ul>
|
||
<li><p>提交你的修改</p>
|
||
<blockquote>
|
||
<div><ul class="simple">
|
||
<li><p>如果是基于GitHub Classroom 开发, 在本地环境或在线codespaces环境下，执行 <code class="docutils literal notranslate"><span class="pre">git</span> <span class="pre">push</span></code> 命令，提交修改的代码到gitub进行CI自动评测。如果评测结果是 红色小叉 （位于repo的中上位置），可进一步点击红色小叉查找具体出错时的CI执行情况。</p></li>
|
||
</ul>
|
||
</div></blockquote>
|
||
</li>
|
||
</ul>
|
||
</div>
|
||
</div>
|
||
<div class="section" id="id2">
|
||
<h2>问答作业<a class="headerlink" href="#id2" title="永久链接至标题">¶</a></h2>
|
||
<ol class="arabic">
|
||
<li><p>请列举 SV39 页表页表项的组成，描述其中的标志位有何作用？</p></li>
|
||
<li><dl>
|
||
<dt>缺页</dt><dd><p>缺页指的是进程访问页面时页面不在页表中或在页表中无效的现象，此时 MMU 将会返回一个中断，
|
||
告知 os 进程内存访问出了问题。os 选择填补页表并重新执行异常指令或者杀死进程。</p>
|
||
<ul class="simple">
|
||
<li><p>请问哪些异常可能是缺页导致的？</p></li>
|
||
<li><p>发生缺页时，描述相关重要寄存器的值，上次实验描述过的可以简略。</p></li>
|
||
</ul>
|
||
<p>缺页有两个常见的原因，其一是 Lazy 策略，也就是直到内存页面被访问才实际进行页表操作。
|
||
比如，一个程序被执行时，进程的代码段理论上需要从磁盘加载到内存。但是 os 并不会马上这样做，
|
||
而是会保存 .text 段在磁盘的位置信息，在这些代码第一次被执行时才完成从磁盘的加载操作。</p>
|
||
<ul class="simple">
|
||
<li><p>这样做有哪些好处？</p></li>
|
||
</ul>
|
||
<p>其实，我们的 mmap 也可以采取 Lazy 策略，比如：一个用户进程先后申请了 10G 的内存空间，
|
||
然后用了其中 1M 就直接退出了。按照现在的做法，我们显然亏大了，进行了很多没有意义的页表操作。</p>
|
||
<ul class="simple">
|
||
<li><p>处理 10G 连续的内存页面，对应的 SV39 页表大致占用多少内存 (估算数量级即可)？</p></li>
|
||
<li><p>请简单思考如何才能实现 Lazy 策略，缺页时又如何处理？描述合理即可，不需要考虑实现。</p></li>
|
||
</ul>
|
||
<p>缺页的另一个常见原因是 swap 策略，也就是内存页面可能被换到磁盘上了，导致对应页面失效。</p>
|
||
<ul class="simple">
|
||
<li><p>此时页面失效如何表现在页表项(PTE)上？</p></li>
|
||
</ul>
|
||
</dd>
|
||
</dl>
|
||
</li>
|
||
<li><p>双页表与单页表</p>
|
||
<p>为了防范侧信道攻击，我们的 os 使用了双页表。但是传统的设计一直是单页表的，也就是说，
|
||
用户线程和对应的内核线程共用同一张页表，只不过内核对应的地址只允许在内核态访问。
|
||
(备注：这里的单/双的说法仅为自创的通俗说法，并无这个名词概念，详情见 <a class="reference external" href="https://en.wikipedia.org/wiki/Kernel_page-table_isolation">KPTI</a> )</p>
|
||
<ul class="simple">
|
||
<li><p>在单页表情况下，如何更换页表？</p></li>
|
||
<li><p>单页表情况下，如何控制用户态无法访问内核页面？（tips:看看上一题最后一问）</p></li>
|
||
<li><p>单页表有何优势？（回答合理即可）</p></li>
|
||
<li><p>双页表实现下，何时需要更换页表？假设你写一个单页表操作系统，你会选择何时更换页表（回答合理即可）？</p></li>
|
||
</ul>
|
||
</li>
|
||
</ol>
|
||
</div>
|
||
<div class="section" id="id3">
|
||
<h2>报告要求<a class="headerlink" href="#id3" title="永久链接至标题">¶</a></h2>
|
||
<ul class="simple">
|
||
<li><p>简单总结你实现的功能（200字以内，不要贴代码）。</p></li>
|
||
<li><p>完成问答题。</p></li>
|
||
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