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POWhy doesn't fill the PTE entry in page fault for vmalloc on ARM Linux Kernel?
 

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  1. POWhy doesn't fill the PTE entry in page fault for vmalloc on ARM Linux Kernel?
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    <p>When page fault happens on VMALLOC_START~VMALLOC_END, why do_translation_fault does not fill Page table entry and just fill PG, PUD and PMD?</p> <p>Corresponding source code @do_translation_fault in arch/arm/mm/fault.c:</p> <pre><code>414 static int __kprobes 415 do_translation_fault(unsigned long addr, unsigned int fsr, 416 struct pt_regs *regs) 417 { 418 unsigned int index; 419 pgd_t *pgd, *pgd_k; 420 pud_t *pud, *pud_k; 421 pmd_t *pmd, *pmd_k; 422 423 if (addr &lt; TASK_SIZE) 424 return do_page_fault(addr, fsr, regs); 425 426 if (user_mode(regs)) 427 goto bad_area; 428 429 index = pgd_index(addr); 430 431 /* 432 * FIXME: CP15 C1 is write only on ARMv3 architectures. 433 */ 434 pgd = cpu_get_pgd() + index; 435 pgd_k = init_mm.pgd + index; 436 437 if (pgd_none(*pgd_k)) 438 goto bad_area; 439 if (!pgd_present(*pgd)) 440 set_pgd(pgd, *pgd_k); 441 442 pud = pud_offset(pgd, addr); 443 pud_k = pud_offset(pgd_k, addr); 444 445 if (pud_none(*pud_k)) 446 goto bad_area; 447 if (!pud_present(*pud)) 448 set_pud(pud, *pud_k); 449 450 pmd = pmd_offset(pud, addr); 451 pmd_k = pmd_offset(pud_k, addr); 452 453 #ifdef CONFIG_ARM_LPAE 454 /* 455 * Only one hardware entry per PMD with LPAE. 456 */ 457 index = 0; 458 #else 459 /* 460 * On ARM one Linux PGD entry contains two hardware entries (see page 461 * tables layout in pgtable.h). We normally guarantee that we always 462 * fill both L1 entries. But create_mapping() doesn't follow the rule. 463 * It can create inidividual L1 entries, so here we have to call 464 * pmd_none() check for the entry really corresponded to address, not 465 * for the first of pair. 466 */ 467 index = (addr &gt;&gt; SECTION_SHIFT) &amp; 1; 468 #endif 469 if (pmd_none(pmd_k[index])) 470 goto bad_area; 471 472 copy_pmd(pmd, pmd_k); 473 return 0; 474 475 bad_area: 476 do_bad_area(addr, fsr, regs); 477 return 0; 478 } </code></pre>
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