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@linuxer：感谢 Linuxer !

希望你们越做越好

@linuxer：@linuxer, 感谢回复, 感谢纠正. 基于kernel的/Documentation/arm64/memory.txt 可以看到 AArch64 Linux memory layout with 4KB pages: Start End Size Use ----------------------------------------------------------------------- 0000000000000000 0000007fffffffff 512GB user ffffff8000000000 ffffffbbfffeffff ~240GB vmalloc ffffffbbffff0000 ffffffbbffffffff 64KB [guard page] ffffffbc00000000 ffffffbdffffffff 8GB vmemmap ffffffbe00000000 ffffffbffbbfffff ~8GB [guard, future vmmemap] ffffffbffa000000 ffffffbffaffffff 16MB PCI I/O space ffffffbffb000000 ffffffbffbbfffff 12MB [guard] ffffffbffbc00000 ffffffbffbdfffff 2MB fixed mappings ffffffbffbe00000 ffffffbffbffffff 2MB [guard] ffffffbffc000000 ffffffbfffffffff 64MB modules ffffffc000000000 ffffffffffffffff 256GB kernel logical memory map 所以我能理解系统启动之后, 所有经过CPU的地址都是虚拟地址吧? 1. directed mapped区域是针对虚拟内存分布而言? 是哪部分呢. 从arch/arm64/mm/init.c打印的virtual kernel memory layout来看是属于[PAGE_OFFSET, (unsigned long)high_memory] 也就是memory 区间. 可以这么理解吗? 2. 拿到虚拟地址之后怎么通过页表换算为实际的物理地址呢? 因为无法知道TTBR1_EL1/TTBR0_EL1的值. 我用current->mm->pgd 和 swapper_pg_dir 分别去算都没有算对. 谢谢

@Z-team：当前估计很难涉及这一块，毕竟人的精力是有限的，时间也是有限的......希望未来有机会吧，哈哈

@vachel：我记得线性地址是X86平台特有的一个术语，在ARMv8中使用虚拟地址这个术语。 对于kmalloc，分配的虚拟地址是位于Directed mapped区域，这个区域的地址虚拟地址和物理地址有固定的线性偏移关系，因此可以使用virt_to_phys。 使用vmalloc，虚拟地址和物理地址没有线性关系。

@macooma：identity mapping实际上是把 物理地址映射到物理地址上去，ARMv8支持的物理地址最大是48个bit，因此高16bit必定等于0

@andreaji：posix_clock_file_operations.owner 不会指向ptp_clock 模块的struct module数据结构的，因为它不属于ptp_clock 模块而是属于posix-clock.c这个模块。当posix-clock.c不是编译成模块而是build in kernel，那么posix_clock_file_operations.owner 等于NULL。

想深入了解下linux kernel中vfs这一subsystem，但是自己读相关的源码很是费力，希望以后能有这一知识的全面介绍，很是期待。

请问ARMv8里面区分线性地址和虚拟地址吗? 比如kmalloc出来的地址通过virt_to_phys转换就能得到PA.但是Vmalloc就不能这么算. 测试方法, 将kmalloc和vmalloc的内存填好固定的值, 打印出对应的PA. 然后通过devmem PA 读对应的内容. 测试代码: //extern struct mm_struct init_mm; pgd_t *pgd; pgd_t *pgd_temp; pmd_t *pmd; pte_t *pte; pud_t *pud; unsigned long va; int* n_kmalloc = (int*)kmalloc(32, GFP_KERNEL); int* n_vmalloc = (int*)vmalloc(sizeof(int)); *n_kmalloc = 0x1234; *n_vmalloc = 0x4321; /**************************************************************test kmalloc**********************************************************/ va = (unsigned long)n_kmalloc; printk(" Test 1, use virt_to_phys get kmalloc PA\n"); printk("kmalloc virt_to_phy = %lx\n ", virt_to_phys(n_kmalloc)); printk(" Test 2, use kernel pgd translation kmalloc to PA \n"); // ffffffc000e88000 B swapper_pg_dir pgd = 0xffffffc000e88000; printk("pgd_index = 0x%x\n", pgd_index(va)); pgd_temp = pgd+pgd_index(va); printk("[%p][%08lx] *pgd = %016llx, pgd = %p, ", n_kmalloc,va, pgd_val(*pgd_temp), pgd_temp); do { if (pgd_none(*pgd_temp) || pgd_bad(*pgd_temp)) break; pud = pud_offset(pgd_temp, va); if (pud_none(*pud) || pud_bad(*pud)) break; pmd = pmd_offset(pud, va); printk(", *pmd=%016llx", pmd_val(*pmd)); if (pmd_none(*pmd) || pmd_bad(*pmd)) break; pte = pte_offset_map(pmd, va); printk(", *pte=%016llx", pte_val(*pte)); } while(0); printk("\n"); printk("Test 3, use mm_struct pgd translation kmalloc to PA\n"); pgd = current->mm->pgd; printk("pgd_index = 0x%x\n", pgd_index(va)); pgd_temp = pgd+pgd_index(va); printk("[%p] [%08lx] *pgd = %016llx, pgd = %p, ", n_kmalloc, va, pgd_val(*pgd_temp), pgd_temp); do { if (pgd_none(*pgd_temp) || pgd_bad(*pgd_temp)) break; pud = pud_offset(pgd_temp, va); if (pud_none(*pud) || pud_bad(*pud)) break; pmd = pmd_offset(pud, va); printk(", *pmd=%016llx", pmd_val(*pmd)); if (pmd_none(*pmd) || pmd_bad(*pmd)) break; pte = pte_offset_map(pmd, va); printk(", *pte=%016llx", pte_val(*pte)); } while(0); printk("\n"); /**************************************************************test vmalloc**********************************************************/ va = (unsigned long)n_vmalloc; printk(" Test 1, use virt_to_phys get vmalloc PA\n"); printk("vmalloc virt_to_phy = %lx\n ", virt_to_phys(n_vmalloc)); printk(" Test 2, use kernel pgd translation vmalloc to PA \n"); // ffffffc000e88000 B swapper_pg_dir pgd = 0xffffffc000e88000; printk("pgd_index = 0x%x\n", pgd_index(va)); pgd_temp = pgd+pgd_index(va); printk("[%p] [%08lx] *pgd = %016llx, pgd = %p, ", n_vmalloc, va, pgd_val(*pgd_temp), pgd_temp); do { if (pgd_none(*pgd_temp) || pgd_bad(*pgd_temp)) break; pud = pud_offset(pgd_temp, va); if (pud_none(*pud) || pud_bad(*pud)) break; pmd = pmd_offset(pud, va); printk(", *pmd=%016llx", pmd_val(*pmd)); if (pmd_none(*pmd) || pmd_bad(*pmd)) break; pte = pte_offset_map(pmd, va); printk(", *pte=%016llx", pte_val(*pte)); } while(0); printk("\n"); printk("Test 3, use mm_struct pgd translation vmalloc to PA\n"); pgd = current->mm->pgd; printk("pgd_index = 0x%x\n", pgd_index(va)); pgd_temp = pgd+pgd_index(va); printk("[%p] [%08lx]*pgd = %016llx, pgd = %p, ", n_vmalloc, va, pgd_val(*pgd_temp), pgd_temp); do { if (pgd_none(*pgd_temp) || pgd_bad(*pgd_temp)) break; pud = pud_offset(pgd_temp, va); if (pud_none(*pud) || pud_bad(*pud)) break; pmd = pmd_offset(pud, va); printk(", *pmd=%016llx", pmd_val(*pmd)); if (pmd_none(*pmd) || pmd_bad(*pmd)) break; pte = pte_offset_map(pmd, va); printk(", *pte=%016llx", pte_val(*pte)); } while(0); printk("\n"); //dump pgd // print_hex_dump(KERN_ERR, "PGD raw data:", DUMP_PREFIX_ADDRESS,16,1,pgd,4096,true); //panic // *(int*)0x2 = 0; /**/ while(true){ } /**/ 测试结论: # [ 4132.980000] Test 1, use virt_to_phys get kmalloc PA [ 4132.984000] kmalloc virt_to_phy = 32184ad40 Test 2, use kernel pgd translation kmalloc to PA [ 4132.992000] pgd_index = 0x102 [ 4132.996000] [ffffffc09d44ad40][ffffffc09d44ad40] *pgd = 000000005d1fa003, pgd = ffffffc000e88810, , *pmd=0040000321800711 [ 4133.008000] Test 3, use mm_struct pgd translation kmalloc to PA [ 4133.012000] pgd_index = 0x102 [ 4133.016000] [ffffffc09d44ad40] [ffffffc09d44ad40] *pgd = 0000000000000000, pgd = ffffffc09ab62810, [ 4133.024000] Test 1, use virt_to_phys get vmalloc PA [ 4133.032000] vmalloc virt_to_phy = ffffffc0260ed000 Test 2, use kernel pgd translation vmalloc to PA [ 4133.040000] pgd_index = 0x0 [ 4133.044000] [ffffff8005eed000] [ffffff8005eed000] *pgd = 000000033ac05003, pgd = ffffffc000e88000, , *pmd=00000000de236003, *pte=02e00003370e3713 [ 4133.056000] Test 3, use mm_struct pgd translation vmalloc to PA [ 4133.060000] pgd_index = 0x0 [ 4133.064000] [ffffff8005eed000] [ffffff8005eed000]*pgd = 0000000000000000, pgd = ffffffc09ab62000, busybox devmem 0x32184ad40 0x00001234 busybox devmem 0xffffffc0260ed000 devmem: mmap: Invalid argument

博主的文章对于我这样初学armv8的晚辈来讲真是提供了极大的参考啊，感谢博主的无私精神！ 有个问题想请教一下，如下： idmap_pg_dir是为turn on MMU准备的一致性映射，物理地址的高16bit都是0，因此identity mapping必定是选择TTBR0_EL1指向的各级地址翻译表。 ------------------------------------------------------------------------------------- 请问这里的“必定”是因何而来呢？ 谢谢！