{"id":50,"date":"2024-03-09T15:02:28","date_gmt":"2024-03-09T07:02:28","guid":{"rendered":"http:\/\/104.46.213.183\/?p=50"},"modified":"2024-03-09T15:02:28","modified_gmt":"2024-03-09T07:02:28","slug":"lab-page-tables","status":"publish","type":"post","link":"https:\/\/www.yewpo.top\/index.php\/50\/","title":{"rendered":"Lab page tables"},"content":{"rendered":"

Lab page tables<\/h1>\n

1 speed up system calls (easy)<\/h2>\n
\n

\u4fee\u6539\u5185\u6838\u4ee3\u7801\uff0c\u5b9e\u73b0\u5bf9\u7cfb\u7edf\u8c03\u7528getpid()<\/code>\u7684\u6027\u80fd\u52a0\u901f\u3002<\/p>\n

\u9898\u76ee\u63d0\u4f9b\u7684\u601d\u8def\uff1a\u5728\u7528\u6237\u7684\u865a\u62df\u5185\u5b58\u4e0a\u6620\u5c04\u4e00\u4e2a\u7269\u7406\u5185\u5b58\u7a7a\u95f4\uff0c\u8be5\u7269\u7406\u7a7a\u95f4\u5185\u5bb9\u5bf9\u7528\u6237\u7a0b\u5e8f\u4ec5\u80fd\u53ea\u8bfb\u3002\u5c06pid<\/code>\u4fe1\u606f\u50a8\u5b58\u5728\u8be5\u7a7a\u95f4\u4e2d\uff0c\u7528\u6237\u8fdb\u7a0b\u76f4\u63a5\u4ece\u8be5\u7a7a\u95f4\u4e2d\u8bfb\u53d6\u3002<\/p>\n<\/blockquote>\n

1.1 \u5206\u6790hints<\/h3>\n

1.1.1 \u524d\u4e09\u6761hints<\/h4>\n

\u524d\u4e09\u6761hints\u603b\u7ed3\u4e00\u53e5\u8bdd\uff0c\u5206\u6790mappages<\/code>\u7684\u529f\u80fd\u3002<\/strong>mappages<\/code>\u51fd\u6570\u539f\u578b\u5728kernel\/vm.c<\/code>\u4e2d\uff0c\u8be5\u51fd\u6570\u7684\u6ce8\u91ca\u5982\u4e0b\uff1a<\/p>\n

\/\/ Create PTEs for virtual addresses starting at va that refer to\n\/\/ physical addresses starting at pa. va and size might not\n\/\/ be page-aligned. Returns 0 on success, -1 if walk() couldn't\n\/\/ allocate a needed page-table page.\nint\nmappages(pagetable_t pagetable, uint64 va, uint64 size, uint64 pa, int perm)<\/code><\/pre>\n
\u901a\u8fc7\u6ce8\u91ca\uff0c\u51fd\u6570\u5c06\u7528\u6237\u7684\u9875\u8868\u4e2d\u91cc\u5efa\u7acb\u865a\u62df\u5730\u5740va\u5f00\u59cb\u7684\u8fde\u7eed\u5927\u5c0f\u4e3asize\u7684\u7a7a\u95f4\u6620\u5c04\u5230\u7269\u7406\u5185\u5b58\u5730\u5740Pa\u5f00\u59cb\u7684\u8fde\u7eed\u5927\u5c0f\u4e3asize\u7684\u7269\u7406\u5185\u5b58\u4e0a\uff0c\u5e76\u5c06\u8fd9\u90e8\u5206\u7a7a\u95f4\u7684\u6743\u9650\u8bbe\u7f6e\u4e3aperm\u3002<\/p>\n
1.1.2 \u540e\u4e24\u6761hints<\/h4>\n
\u63d0\u9192\u60a8\u4e0d\u8981\u5fd8\u8bb0\u5206\u914d\u548c\u91ca\u653e\u4e86\uff01\uff01\u4f46\u662f\u8fd9\u4e2a\u63d0\u793a\u6709\u4e00\u70b9\u70b9\u7684\u7a81\u5140\uff0c\u6ca1\u6df1\u5165\u7406\u89e3\u524d\u4e0d\u77e5\u9053\u5728\u8bb2\u5565\uff1f<\/p>\n
1.2 \u5b66\u4e60proc_pagetable(struct proc *p)<\/h3>\n
\u4f5c\u4e3ahints\u7684\u7b2c\u4e00\u6761\uff0c\u8fd9\u4e00\u6761\u7684\u5b9e\u9645\u4ef7\u503c\u5728\u6b64\u65f6\u5c31\u6210\u4e3a\u4e86\u5b66\u4e60proc_pagetable<\/code>\u5bf9mappages<\/code>\u51fd\u6570\u7684\u4f7f\u7528\u793a\u4f8b\u3002\u6211\u6765\u63cf\u8ff0\u4e00\u4e0b\u4e0b\u5217\u4f8b\u5b50\u3002<\/p>\n
if(mappages(pagetable, TRAPFRAME, PGSIZE,\n              (uint64)(p->trapframe), PTE_R | PTE_W) < 0){\n    uvmunmap(pagetable, TRAMPOLINE, 1, 0);\n    uvmfree(pagetable, 0);\n    return 0;\n}<\/code><\/pre>\n
\u8fd9\u4e2amap\u7684\u4f7f\u7528\uff0c\u5c31\u662f\u5728pagetable\u8fd9\u4e2a\u9875\u8868\u4e2d\u5efa\u7acb\u4ece\u865a\u62df\u5730\u5740TRAPFRAME<\/code>\uff08\u5df2\u7ecf\u5728memlayout.h\u4e2d\u58f0\u660e\uff09\u5230\u7269\u7406\u5185\u5b58\u5730\u5740p->trapframe<\/code>\u7684\u5927\u5c0f\u4e3aPGSIZE<\/code>\u7684\u6620\u5c04\uff0c\u4e14\u6743\u9650\u4e3aPTE_R | PTE_W<\/code>\uff0c\u8868\u793a\u7528\u6237\u53ef\u8bfb\u53ef\u5199\u3002<\/p>\n
\u5982\u679c\u6620\u5c04\u5931\u8d25\u4e86\uff0c\u4e0b\u9762\u4e24\u6b65\u7684\u64cd\u4f5c\u5206\u6790\u4e5f\u975e\u5e38\u91cd\u8981\uff0c\u540e\u9762\u7684BUG\u5c31\u8981\u7528\u5230\u8fd9\u4e00\u70b9\u5206\u6790<\/strong><\/p>\n
\u9996\u5148\u662fuvmumap<\/code>\u51fd\u6570\uff0c\u67e5\u770b\u51fd\u6570\u539f\u578b\u7684\u89e3\u91ca\uff0c\u8be5\u51fd\u6570\u662f\u89e3\u9664\u5728pagetable\u4e2d\u7684\u5173\u4e8e\u865a\u62df\u5730\u5740TRAmpoline<\/code>\u7684\u6620\u5c04\u5173\u7cfb\u3002\u5f71\u54cd\u7684\u9875\u9762\u5927\u5c0f\u4e3a1\u4e2aPGSIZE\uff0c\u6700\u540e\u4e00\u4e2a\u53c2\u6570\u662f\u8868\u793a\u8981\u4e0d\u8981\u91ca\u653e\u6389\u5bf9\u5e94\u7684\u7269\u7406\u5185\u5b58\uff0c\u8be5\u4f4d\u7f6e\u4e8e0\u7684\u539f\u56e0\u662f\uff0c\u91ca\u653e\u7269\u7406\u5185\u5b58\u7684\u64cd\u4f5c\u5728uvmfree<\/code>\u51fd\u6570\u4e2d\u6253\u5305\u5b8c\u6210\u4e86\u3002\u8fd9\u4e2a\u51fd\u6570\u6709\u4e00\u4e2a\u4f7f\u7528\u6761\u4ef6\uff0c\u5c31\u662f\u8981\u89e3\u9664\u7684\u6620\u5c04\u5173\u7cfb\u8981\u4e00\u5b9a\u5b58\u5728\uff0c\u90a3\u8fd9\u4e2a\u91ca\u653e\u7684TRAMPOLINE<\/code>\u6620\u5c04\u5173\u7cfb\uff0c\u662f\u5728\u521b\u5efaTRAPFRAME<\/code>\u6620\u5c04\u4e4b\u524d\u5c31\u5df2\u7ecf\u521b\u5efa\u4e86\uff0c\u6240\u4ee5\u8be5\u6620\u5c04\u4e00\u5b9a\u5b58\u5728\uff0c\u5728\u6b64\u65f6\u4e5f\u5f97\u89e3\u9664\u8fd9\u4e2a\u6620\u5c04\u5173\u7cfb\u3002<\/strong><\/p>\n
\u90a3uvmfree<\/code>\u51fd\u6570\u7684\u529f\u80fd\u5c31\u662f\u6e05\u9664pagetable\u8fd9\u4e2a\u9875\u8868\u91cc\u7684\u4fe1\u606f\u3002<\/p>\n
\n
\u5206\u6790\u5230\u8fd9\u4e00\u6b65\u7684\u65f6\u5019\uff0c\u4f60\u5e94\u8be5\u4f1a\u60f3\uff0c\u865a\u62df\u5730\u5740USYSCALL<\/code>\u5df2\u7ecf\u544a\u8bc9\u4f60\u4e86\uff0c\u4f46\u662f\u7269\u7406\u5185\u5b58\u5730\u5740\u634f\uff1f\uff1f\uff1f\uff1f<\/p>\n
1.3 \u5206\u914d\u4e00\u4e2a\u7269\u7406\u5185\u5b58<\/h3>\n
\u5f53\u7136\u4e5f\u4e0d\u80fd\u968f\u4fbf\u6307\u5b9a\u4e00\u4e2a\u5730\u5740\u8fdb\u884c\u5206\u914d\u662f\u5427\uff0c\u6b64\u65f6\u8054\u60f3\u5230sys_trace<\/code>\u5b9e\u9a8c\uff0c\u81ea\u5df1\u5728proc<\/code>\u7ed3\u6784\u4f53\u4e2d\u5b9a\u4e49\u4e86\u4e00\u4e2atrace_s<\/code>\u6765\u8868\u793a\u8981\u8ffd\u8e2a\u7684syscall\u7684\u7801\u56fe\u3002\u6b64\u65f6\uff0c\u6211\u4eec\u53ef\u4ee5\u521b\u5efa\u4e00\u4e2a\u6307\u9488\u8868\u793a\u7528\u6237\u6001\u548c\u5185\u6838\u6001\u8d21\u732e\u7684usyscall<\/code>\u7a7a\u95f4\u7684\u8d77\u59cb\u5730\u5740\u3002<\/p>\n
\u6b64\u65f6\uff0c\u6700\u540e\u4e24\u6761hints\u5c31\u6709\u610f\u4e49\u4e86\uff0c\u5c31\u662f\u8981\u5206\u914d\u8fd9\u4e2a\u7a7a\u95f4\u548c\u521d\u59cb\u5316\u8fd9\u4e2a\u7a7a\u95f4\uff0c\u5f53\u8fdb\u7a0b\u7ed3\u675f\u7684\u65f6\u5019\u4e5f\u5c31\u8981\u91ca\u653e\u8fd9\u4e2a\u7a7a\u95f4\u3002<\/p>\n
\u5728kernel\/kalloc.c<\/code>\u4e2d\u7684kalloc()<\/code>\u53ef\u4ee5\u5b9e\u73b0\u7269\u7406\u5185\u5b58\u7684\u5206\u914d\uff0c\u6bcf\u6b21\u5206\u914d\u5927\u5c0f\uff0c\u4e00\u4e2apgsize\u3002<\/p>\n
\u6a21\u4eff\u5df2\u6709\u4ee3\u7801\uff0c\u5206\u914d\u8fd9\u4e2a\u7a7a\u95f4\uff0c\u5e76\u5728\u8be5\u7a7a\u95f4\u7684\u8d77\u59cb\u4f4d\u7f6e\u8d4b\u503cpid\u3002<\/p>\n
if ((p->sharepage = (uint64)kalloc()) == 0) {\n    freeproc(p);\n    release(&p->lock);\n    return 0;\n}\n\n((struct usyscall *)p->sharepage)->pid = p->pid;<\/code><\/pre>\n
1.4 \u5efa\u7acb\u6620\u5c04\u5173\u7cfb<\/h3>\n
\u6709\u4e86\u7269\u7406\u5730\u5740\u540e\uff0c\u6620\u5c04\u5173\u7cfb\u5c31\u597d\u5efa\u7acb\u4e86\u3002<\/p>\n
if (mappages(pagetable, USYSCALL, PGSIZE,\n             p->sharepage, PTE_R | PTE_U) < 0) {\n    uvmunmap(pagetable, TRAMPOLINE, 1, 0);\n    uvmunmap(pagetable, TRAPFRAME, 1, 0);\n    uvmfree(pagetable, 0);\n}<\/code><\/pre>\n
\u5982\u679c\u6620\u5c04\u5931\u8d25\u4e86\uff0c\u4e00\u5b9a\u8981\u89e3\u9664\u4e4b\u524d\u5efa\u7acb\u597d\u7684\u6620\u5c04\u5173\u7cfb<\/strong><\/p>\n
1.5 \u91ca\u653e\u5185\u5b58<\/h3>\n
\u6a21\u4efffreeproc<\/code>\u51fd\u6570\uff0c\u91ca\u653e\u81ea\u5df1\u5b9a\u4e49\u7684\u5185\u5b58\u6307\u9488\u7a7a\u95f4\u3002<\/p>\n
if (p->sharepage) {\n    kfree((void *)p->sharepage);\n}\np->sharepage = 0;<\/code><\/pre>\n
1.6 \u5148\u81ea\u4fe1\u5730\u5b8c\u6210\u8fd9\u4e2a\u5c0f\u5b9e\u9a8c<\/h3>\n
\u5e0c\u671b\u8d8a\u5927\u5931\u671b\u8d8a\u5927\uff0c\u8fd0\u884c\u4fee\u6539\u7684\u5185\u6838\u4ee3\u7801\u540e\uff0c\u53d1\u73b0\u7cfb\u7edf\u542f\u52a8\u4e0d\u4e86\u4e86QAQ\u3002<\/p>\n
xv6 kernel is booting\n\nhart 2 starting\nhart 1 starting\npanic: freewalk: leaf<\/code><\/pre>\n
\u5bc4<\/p>\n
1.7 DEBUG<\/h3>\n
\u901a\u8fc7\u624b\u52a8\u751f\u6210\u8c03\u8bd5\u4fe1\u606f\uff0c\u53d1\u73b0\u65e2\u4e0d\u662f\u5206\u914d\u7a7a\u95f4\u7684\u95ee\u9898\uff0c\u4e5f\u4e0d\u662f\u6620\u5c04\u5173\u7cfb\u7684\u95ee\u9898\uff0c\u53ef\u80fd\u662f\u91ca\u653e\u7684\u95ee\u9898\u3002\u627e\u627e\u8fd9\u4e2a\u62a5\u9519\u4fe1\u606f\u6765\u6e90\uff0c\u53d1\u73b0\u662f\u5728kernel\/vm.c<\/code>\u7684freewalk<\/code>\u51fd\u6570\u4e2d\uff0c\u9519\u8bef\u6761\u4ef6\u5982\u4e0b\uff1a<\/p>\n
if(pte & PTE_V){\n    panic("freewalk: leaf");\n}<\/code><\/pre>\n
\u610f\u601d\u662f\u5728\u91ca\u653e\u8fd9\u4e2a\u9875\u8868\u7684\u65f6\u5019\uff0c\u5b58\u5728\u6709\u6548\u7684\u6620\u5c04\u5173\u7cfb\u3002\u8fd9\u65f6\u5019\u60f3\u60f3\uff0c\u4e5f\u53ea\u6709\u81ea\u5df1\u5199\u7684\u6620\u5c04\u5173\u7cfb\u6ca1\u6709\u89e3\u9664\u4e86\u3002<\/p>\n
\u5728\u770b\u770bfreeproc<\/code>\u51fd\u6570\uff0c\u53d1\u73b0\u8fd9\u4e2a\u51fd\u6570\u8c03\u7528\u4e86proc_freepagetable<\/code>\u51fd\u6570\uff0c\u518d\u770b\u770b\u8fd9\u4e2a\u51fd\u6570\uff1a<\/p>\n
void\nproc_freepagetable(pagetable_t pagetable, uint64 sz)\n{\n  uvmunmap(pagetable, TRAMPOLINE, 1, 0);\n  uvmunmap(pagetable, TRAPFRAME, 1, 0);\n  uvmfree(pagetable, sz);\n}<\/code><\/pre>\n
\u679c\u7136\uff0c\u6ca1\u6709\u89e3\u9664\u81ea\u5df1\u5efa\u7acb\u7684USYSCALL<\/code>\u7684\u6620\u5c04\u5173\u7cfb\u3002\u6dfb\u52a0\u8fd9\u4e00\u884c\uff1a<\/p>\n
uvmunmap(pagetable, USYSCALL, 1, 0);<\/code><\/pre>\n
\u518d\u6d4b\u8bd5\u4e00\u4e0b\uff1aOK\uff01\uff01\uff01<\/p>\n
1.8 Which other xv6 system call(s) could be made faster using this shared page? Explain how.<\/h3>\n
Candidate are:\n    getpid()\n    uptime()\n    fstate()?<\/code><\/pre>\n
\u8fd9\u4e9b\u51fd\u6570\u53ea\u9700\u8981\u83b7\u5f97\u4fe1\u606f\u5373\u53ef\uff0c\u4e0d\u9700\u8981\u4fee\u6539\u4fe1\u606f\uff0c\u6240\u4ee5\u5c06\u8fd9\u4e9b\u4fe1\u606f\u653e\u5728\u5171\u4eab\u5185\u5b58\u4e2d\u76f4\u63a5\u62ff\u53d6\u5373\u53ef\u3002<\/p>\n
2 Print a page table (easy)<\/h2>\n
\n
\u7f16\u5199\u4e00\u4e2a\u51fd\u6570\u5b9e\u73b0\u6253\u5370\u9875\u8868\u4fe1\u606f<\/p>\n<\/blockquote>\n
\u6839\u636e\u63d0\u793a\uff0c\u4fee\u6539exec.c<\/code>\u4ee3\u7801\uff0c\u6a21\u4efffreewalk<\/code>\u51fd\u6570\uff0c\u5c06\u5176\u4e2d\u7684\u91ca\u653e\u6539\u5199\u6210\u6253\u5370\u76f8\u5173\u4fe1\u606f\u5373\u53ef\uff0c\u5e76\u5728kernel\/defs.h<\/code>\u4e2d\u58f0\u660e\u8fd9\u4e2a\u51fd\u6570\u3002\u53ea\u7528\u5904\u7406\u6253\u5370\u201c..\u201d\u5373\u53ef\u3002<\/p>\n
2.1 \u4ee3\u7801\u5b9e\u73b0<\/h3>\n
void\nvmprint(pagetable_t pagetable) {\n    static int deep = 1;\n\n    for(int i = 0; i < 512; i++){\n        pte_t pte = pagetable[i];\n\n        if (pte & PTE_V) {\n            for (int j = 1; j < deep; ++j) {\n                printf(".. ");\n            }\n        }\n\n        if((pte & PTE_V) && (pte & (PTE_R|PTE_W|PTE_X)) == 0){\n            printf("..%d: pte %p pa %p\\n", i, pte, PTE2PA(pte));\n            uint64 child = PTE2PA(pte);\n            deep++;\n            vmprint((pagetable_t)child);\n            deep--;\n        } else if(pte & PTE_V){\n            printf("..%d: pte %p pa %p\\n", i, pte, PTE2PA(pte));\n        }\n    }\n}<\/code><\/pre>\n
2.2 \u9898\u76ee\u95ee\u9898<\/h3>\n
Explain the output of vmprint<\/code> in terms of Fig 3-4 from the text. What does page 0 contain? What is in page 2? When running in user mode, could the process read\/write the memory mapped by page 1? What does the third to last page contain?<\/p>\n
\n
\u901a\u8fc7\u5bf9exec<\/code>\u51fd\u6570\u7684\u5206\u6790\uff0c\u9996\u5148\u4ece\u5185\u5b58\u4e2d\u52a0\u8f7d\u7a0b\u5e8f\u5230\u7b2c\u4e00\u4e2a\u9875\u8868\u4e2d\uff0c\u6240\u4ee5page 0 \u5305\u542b\u4e00\u4e2a\u8fdb\u7a0b\u9700\u8981\u7684\u4fe1\u606f\uff1b\u7136\u540e\uff0cexec<\/code>\u51fd\u6570\u5728\u7d27\u63a5\u7740\u7684\u9875\u8868\u4e2d\u5206\u914d\u4e24\u9875\uff0cpage 1 \u662f\u5b88\u62a4\u9875\u9762\uff0cpage 2 \u662f\u8fdb\u7a0b\u6808\u9875\u9762\uff0c\u8be5\u6808\u91cc\u5b58\u653e\u7a0b\u5e8f\u8fd0\u884c\u65f6\u7684\u53d8\u91cf\u3002\u56e0\u4e3apage 1\u662f\u5b88\u62a4\u9875\u9762\uff0c\u7528\u6237\u4e0d\u80fd\u8bbf\u95ee\u3002\u5012\u6570\u4e09\u9875\u5206\u522b\u662f\u8df3\u677f\u9875\u9762\uff0c\u8f6c\u50a8\u9875\u9762\u548c\u7528\u6237\u548c\u5185\u5b58\u7684\u5171\u4eab\u9875\u9762\u3002<\/p>\n
ph.vaddr: 0x0000000000000000 ph.memsz: 0x0000000000001000\nph.vaddr: 0x0000000000001000 ph.memsz: 0x0000000000000030\npage table 0x0000000087f6b000\n..0: pte 0x0000000021fd9c01 pa 0x0000000087f67000\n.. ..0: pte 0x0000000021fd9801 pa 0x0000000087f66000\n.. .. ..0: pte 0x0000000021fda01b pa 0x0000000087f68000\n.. .. ..1: pte 0x0000000021fd9417 pa 0x0000000087f65000\n.. .. ..2: pte 0x0000000021fd9007 pa 0x0000000087f64000\n.. .. ..3: pte 0x0000000021fd8c17 pa 0x0000000087f63000\n..255: pte 0x0000000021fda801 pa 0x0000000087f6a000\n.. ..511: pte 0x0000000021fda401 pa 0x0000000087f69000\n.. .. ..509: pte 0x0000000021fdcc13 pa 0x0000000087f73000\n.. .. ..510: pte 0x0000000021fdd007 pa 0x0000000087f74000\n.. .. ..511: pte 0x0000000020001c0b pa 0x0000000080007000\ninit: starting sh\nph.vaddr: 0x0000000000000000 ph.memsz: 0x0000000000002000\nph.vaddr: 0x0000000000002000 ph.memsz: 0x0000000000000098<\/code><\/pre>\n
3 Detect which pages have been accessed (hard)<\/h2>\n
\n
\u7f16\u5199\u7cfb\u7edf\u8c03\u4f63\u51fd\u6570pgacess<\/code>\uff0c\u6765\u8ffd\u8e2a\u90a3\u4e9b\u9875\u9762\u88ab\u4f7f\u7528\u8fc7\u3002<\/p>\n
pgacess\u8c03\u4f63\u4f20\u9012\u4e09\u4e2a\u53c2\u6570\uff0c\u7b2c\u4e00\u4e2a\u53c2\u6570\u662f\u8981\u67e5\u8be2\u7684\u9875\u8868\u7684\u8d77\u59cb\u865a\u62df\u5730\u5740\uff1b\u7b2c2\u4e2a\u53c2\u6570\u662f\u8981\u67e5\u8be2\u7684\u9875\u9762\u7684\u4e2a\u6570\uff1b\u7b2c3\u4e2a\u53c2\u6570\u662f\u7528\u6237\u7a7a\u95f4\u7684\u7801\u56fe\u5730\u5740\uff0c\u8be5\u7801\u56fe\u8868\u793a\u9875\u9762\u88ab\u4f7f\u7528\u7684\u60c5\u51b5\u3002<\/p>\n<\/blockquote>\n
3.1 \u83b7\u5f97\u8fd9\u4e09\u4e2a\u53c2\u6570<\/h3>\n
\u8fd9\u4e09\u4e2a\u53c2\u6570\u5206\u522b\u5b58\u653e\u5728trapframe<\/code>\u4e2d\u7684a0\uff0ca1, a2<\/code>\u4e09\u4e2a\u4f4d\u7f6e\u4e0a\uff0c\u4e09\u4e2a\u53c2\u6570\u4e5f\u5206\u522b\u4f7f\u7528argaddr, argint, argaddr<\/code>\u51fd\u6570\u5f97\u5230\u3002<\/p>\n
uint64 va;\nint sz;\nuint64 user_bitmask_addr;\n\nargaddr(0, &va);\nargint(1, &sz);\nargaddr(2, &user_bitmask_addr);<\/code><\/pre>\n
\u7531\u4e8e\u8868\u793a\u7684\u8303\u56f4\u6709\u9650\uff0c\u6240\u4ee5\u6211\u4eec\u8981\u5bf9\u67e5\u8be2\u7684\u9875\u9762\u6570\u6709\u9650\u5236\u3002\u56e0\u4e3aint\u7684\u6570\u4f4d\u670932\u4f4d\uff0c\u6240\u4ee5\u6211\u4eec\u9650\u5236\u6700\u5927\u7684\u67e5\u8be2\u5927\u5c0f\u4e3a32\u3002<\/p>\n
if (sz > 32) {\n    return -1;\n}<\/code><\/pre>\n
3.2 \u5206\u6790walk\u51fd\u6570<\/h3>\n
\n
walk\u51fd\u6570\u7684\u4f5c\u7528\u662f\u901a\u8fc7\u865a\u62df\u5730\u5740\uff0c\u627e\u5230\u5bf9\u5e94\u7684\u9875\u8868\u4e2d\u7684\u989dPTE\u3002<\/p>\n<\/blockquote>\n
xv6\u7cfb\u7edf\u91c7\u7528\u7684\u662f\u4e09\u7ea7\u9875\u8868\uff0c\u865a\u62df\u5730\u5740\u4e2d[38:30]\u662f\u4e00\u7ea7\u9875\u8868\u6307\u9488satp<\/code>\uff0c\u6216\u8005\u7406\u89e3\u4e3a\u9875\u8868\u4e2d\u5bf9\u5e94\u7684PTE\u7684\u7f16\u53f7\uff08\u4ece0\u5230511\uff09\uff0c[29:21]\u662f\u4e8c\u7ea7\u9875\u8868\u6307\u9488\uff0c[20:12]\u662f\u4e09\u7ea7\u9875\u8868\u6307\u9488\u3002<\/p>\n
pte_t *\nwalk(pagetable_t pagetable, uint64 va, int alloc)\n{\n  if(va >= MAXVA)\n    panic("walk");\n\n  for(int level = 2; level > 0; level--) {\n    pte_t *pte = &pagetable[PX(level, va)];\n    if(*pte & PTE_V) {\n      pagetable = (pagetable_t)PTE2PA(*pte);\n    } else {\n      if(!alloc || (pagetable = (pde_t*)kalloc()) == 0)\n        return 0;\n      memset(pagetable, 0, PGSIZE);\n      *pte = PA2PTE(pagetable) | PTE_V;\n    }\n  }\n  return &pagetable[PX(0, va)];\n}<\/code><\/pre>\n
\u8fd9\u4e2a\u51fd\u6570\u5148\u4f20\u9012\u4e00\u4e2a\u8fdb\u7a0b\u7684\u6839\u9875\u8868\uff0c\u5e76\u7531\u4e00\u7ea7\u9875\u8868\u6307\u9488\u7684\u6307\u5411\u83b7\u5f97\u4e00\u4e2aPTE\uff0c\u5373\u83b7\u5f97\u4e00\u4e2a\u5230\u4e0b\u7ea7\u9875\u8868\u7684\u6620\u5c04\u5173\u7cfb\uff0c\u6b64\u65f6\u9875\u8868\u66f4\u65b0\u4e3a\u4e0b\u7ea7\u9875\u8868\uff0c\u5728\u8be5\u9875\u8868\u7528\u4e8c\u7ea7\u9875\u8868\u6307\u9488\u83b7\u53d6\u5230\u4e0b\u4e00\u7ea7\u9875\u8868\u7684\u6620\u5c04\u5173\u7cfb\u3002\u518d\u91cd\u590d\u4e00\u904d\u8fd9\u4e2a\u8fc7\u7a0b\uff0c\u5c31\u53ef\u4ee5\u5f97\u5230\u6620\u5c04\u5230\u7269\u7406\u5185\u5b58\u7684\u4e00\u4e2a\u6620\u5c04\u5173\u7cfbPTE\uff0c\u5e76\u4e14\u8fd4\u56de\u4ed6\u7684\u6307\u9488\u3002<\/p>\n
3.3 \u83b7\u53d6PTE_A\u4f4d<\/h3>\n
\u5728\u53c2\u8003\u6559\u6750\u5f97\u5230\uff0cPTE\u7684flag\u7684\u7b2c7\u4f4d\uff08\u504f\u79fb6\uff09\u4e3aPTE_A\uff0c\u8868\u793a\u8be5PTE\u662f\u5426\u88ab\u4f7f\u7528\u8fc7\u3002\u6211\u4eec\u5728kernel\/risc.v<\/code>\u4e2d\u58f0\u660e\u8fd9\u4e00\u4f4d\u3002<\/p>\n
#define PTE_A (1L << 6)<\/code><\/pre>\n
\u5728\u4ee3\u7801\u4e2d\uff0c\u7528&\u4f4d\u8fd0\u7b97\u5c31\u53ef\u4ee5\u63d0\u53d6\u51fa\u8fd9\u4e00\u4f4d\uff0c\u7528^\u4f4d\u8fd0\u7b97\u5c31\u53ef\u4ee5\u5c06\u8fd9\u4e00\u4f4d\u8bbe\u7f6e\u4e3a0\uff0c\u5982\u679c\u8fd9\u4e00\u4f4d\u6709\u503c\u7684\u8bdd\u3002<\/p>\n
3.4 \u8bbe\u7f6ebitmask<\/h3>\n
\u4eceva\u5f00\u59cb\uff0c\u904d\u5386\u5927\u5c0f\u4e3asz\u7684\u9875\u8868\uff0c\u5982\u679cPTE\u7684PTE_A\u4f4d\u4e3a1\uff0c\u5219\u5728bitmask\u4e2d\u7684\u6539\u67e5\u8be2\u9875\u8868\u7f16\u53f7\u4e3a\u7f6e1\uff0c\u5e76\u5c06PTE_A\u7f6e0\uff0c\u8868\u793a\u8fd9\u4e2a\u72b6\u6001\u6211\u4eec\u5df2\u7ecf\u67e5\u8be2\u8fc7\u4e86\u3002<\/p>\n
for (int i = 0; i < sz; ++i) {\n    pte_t * pte = walk(p->pagetable, va, 0);\n\n    if ((*pte) & PTE_A) {\n        bitmask |= (1 << i);\n        (*pte) ^= PTE_A;\n    }\n\n    va += PGSIZE;\n}<\/code><\/pre>\n
3.5 \u51fd\u6570\u5b9e\u73b0<\/h3>\n
\u6700\u540e\u5c06bitmask\u7528copyout<\/code>\u51fd\u6570\u590d\u5236\u5230\u7528\u6237\u7a7a\u95f4\u4e0a\u5373\u53ef\u3002<\/p>\n
int\nsys_pgaccess(void)\n{\n  uint64 va;\n  int sz;\n  uint64 user_bitmask_addr;\n  int bitmask = 0;\n  struct proc * p = myproc();\n\n  argaddr(0, &va);\n  argint(1, &sz);\n  argaddr(2, &user_bitmask_addr);\n\n  if (sz > 32) {\n      return -1;\n  }\n\n  for (int i = 0; i < sz; ++i) {\n      pte_t * pte = walk(p->pagetable, va, 0);\n\n      if ((*pte) & PTE_A) {\n          bitmask |= (1 << i);\n          (*pte) ^= PTE_A;\n      }\n\n      va += PGSIZE;\n  }\n\n  if (copyout(p->pagetable, user_bitmask_addr, (char *)&bitmask, sizeof(bitmask)) < 0) {\n      return -1;\n  }\n\n  return 0;\n}<\/code><\/pre>\n
\u7f16\u8bd1\u6d4b\u8bd5\uff0c\u7136\u540e\u901a\u8fc7\u3002<\/p>\n
4 END<\/h2>\n
\u5b9e\u9a8c\u7ed3\u675f\uff0c\u6d4b\u8bd5\u7684\u7ed3\u679c\u5982\u4e0b\u3002<\/p>\n
== Test pgtbltest == \n$ make qemu-gdb\n(3.8s) \n== Test   pgtbltest: ugetpid == \n  pgtbltest: ugetpid: OK \n== Test   pgtbltest: pgaccess == \n  pgtbltest: pgaccess: OK \n== Test pte printout == \n$ make qemu-gdb\npte printout: OK (1.2s) \n== Test answers-pgtbl.txt == answers-pgtbl.txt: OK \n== Test usertests == \n$ make qemu-gdb\n(208.4s) \n== Test   usertests: all tests == \n  usertests: all tests: OK\n== Test time == \ntime: OK \nScore: 46\/46<\/code><\/pre>\n","protected":false},"excerpt":{"rendered":"
xv6\u64cd\u4f5c\u7cfb\u7edf\u5b9e\u9a8c3\u3002<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4],"tags":[14],"class_list":["post-50","post","type-post","status-publish","format-standard","hentry","category-os","tag-xv6"],"_links":{"self":[{"href":"https:\/\/www.yewpo.top\/index.php\/wp-json\/wp\/v2\/posts\/50","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.yewpo.top\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.yewpo.top\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.yewpo.top\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.yewpo.top\/index.php\/wp-json\/wp\/v2\/comments?post=50"}],"version-history":[{"count":0,"href":"https:\/\/www.yewpo.top\/index.php\/wp-json\/wp\/v2\/posts\/50\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.yewpo.top\/index.php\/wp-json\/wp\/v2\/media?parent=50"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.yewpo.top\/index.php\/wp-json\/wp\/v2\/categories?post=50"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.yewpo.top\/index.php\/wp-json\/wp\/v2\/tags?post=50"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}