鸿蒙轻内核A核源码分析系列五 虚实映射
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2、 虚拟映射初始化
在文件kernel/base/vm/los_vm_boot.c
中的系统内存初始化函数OsSysMemInit()
会调用虚实映射初始化函数OsInitMappingStartUp()
。该函数代码定义在文件arch/arm/arm/src/los_arch_mmu.c
,代码如下。⑴处函数使TLB失效,清理虚实映射缓存数据,涉及些cp15寄存器和汇编,后续再分析。⑵处函数切换到临时TTB。⑶处设置内核地址空间的映射。下面分别详细这些函数代码。
2.1 函数OsSwitchTmpTTB
函数OsSwitchTmpTTB
申请16KiB的内存存放L1页表项数据,把页表项数据从g_firstPageTable
复制到申请的内存区域。⑴处获取内核地址空间。L1页表由4096个页表项组成,每个4 bytes,共需要16KiB大小。所以⑵处代码按16KiB对齐申请16KiB大小的内存区域存放L1页表项。⑶处设置内核虚拟内存地址空间的转换表基地址TTB。⑷处把g_firstPageTable
页表数据复制到内核地址空间的转换表区域。如果复制失败,则直接使用g_firstPageTable
。⑸处设置内核虚拟地址空间的TTB转换地址对应的物理内存地址,然后调用函数OsArmWriteTtbr0
写入MMU寄存器。
2.2 函数OsSetKSectionAttr
内部函数OsSetKSectionAttr
用于设置内核虚拟地址空间的区间属性,分别针对内核虚拟地址空间的内核区间[KERNEL_ASPACE_BASE,KERNEL_ASPACE_BASE+KERNEL_ASPACE_SIZE]和未缓存区间[UNCACHED_VMM_BASE,UNCACHED_VMM_BASE+UNCACHED_VMM_SIZE]进行设置。内核虚拟地址空间是固定映射到物理内存的,内核地址空间的映射包含代码段、数据段、堆栈区间映射,如下示意图所示:

⑴处计算相对内核虚拟地址空间基地址KERNEL_VMM_BASE
的偏移大小。⑵处先计算相对偏移值的text、rodata、data_bss段的虚拟内存地址,然后创建这些段的虚实映射关系数组mmuKernelMappings
。⑶处设置内核虚拟地址区间的虚拟转换基地址TTB和物理转换基地址TTB。然后解除虚拟地址virtAddr
的虚实映射,解除映射的长度就是代码段、只读数据段、数据BSS段这些内存段的长度。⑷处按指定的标签flags
对text代码段之前的内存区间进行虚实映射。⑸处映射text代码段、rodata只读数据段、data_bss数据段的内存区间,并调用函数LOS_VmSpaceReserve
在进程空间中预定地址区间。⑹是BSS段后面的heap区、stack区的映射,映射虚拟地址空间的内存堆栈区间到对应的物理内存区间。
STATIC VOID OsSetKSectionAttr(UINTPTR virtAddr, BOOL uncached)
{
⑴ UINT32 offset = virtAddr - KERNEL_VMM_BASE;
⑵ UINTPTR textStart = (UINTPTR)&__text_start + offset;
UINTPTR textEnd = (UINTPTR)&__text_end + offset;
UINTPTR rodataStart = (UINTPTR)&__rodata_start + offset;
UINTPTR rodataEnd = (UINTPTR)&__rodata_end + offset;
UINTPTR ramDataStart = (UINTPTR)&__ram_data_start + offset;
UINTPTR bssEnd = (UINTPTR)&__bss_end + offset;
UINT32 bssEndBoundary = ROUNDUP(bssEnd, MB);
LosArchMmuInitMapping mmuKernelMappings[] = {
{
.phys = SYS_MEM_BASE + textStart - virtAddr,
.virt = textStart,
.size = ROUNDUP(textEnd - textStart, MMU_DESCRIPTOR_L2_SMALL_SIZE),
.flags = VM_MAP_REGION_FLAG_PERM_READ | VM_MAP_REGION_FLAG_PERM_EXECUTE,
.name = "kernel_text"
},
{
.phys = SYS_MEM_BASE + rodataStart - virtAddr,
.virt = rodataStart,
.size = ROUNDUP(rodataEnd - rodataStart, MMU_DESCRIPTOR_L2_SMALL_SIZE),
.flags = VM_MAP_REGION_FLAG_PERM_READ,
.name = "kernel_rodata"
},
{
.phys = SYS_MEM_BASE + ramDataStart - virtAddr,
.virt = ramDataStart,
.size = ROUNDUP(bssEndBoundary - ramDataStart, MMU_DESCRIPTOR_L2_SMALL_SIZE),
.flags = VM_MAP_REGION_FLAG_PERM_READ | VM_MAP_REGION_FLAG_PERM_WRITE,
.name = "kernel_data_bss"
}
};
LosVmSpace *kSpace = LOS_GetKVmSpace();
status_t status;
UINT32 length;
int i;
LosArchMmuInitMapping *kernelMap = NULL;
UINT32 kmallocLength;
UINT32 flags;
⑶ kSpace->archMmu.virtTtb = (PTE_T *)g_firstPageTable;
kSpace->archMmu.physTtb = LOS_PaddrQuery(kSpace->archMmu.virtTtb);
status = LOS_ArchMmuUnmap(&kSpace->archMmu, virtAddr,
(bssEndBoundary - virtAddr) >> MMU_DESCRIPTOR_L2_SMALL_SHIFT);
if (status != ((bssEndBoundary - virtAddr) >> MMU_DESCRIPTOR_L2_SMALL_SHIFT)) {
VM_ERR("unmap failed, status: %d", status);
return;
}
flags = VM_MAP_REGION_FLAG_PERM_READ | VM_MAP_REGION_FLAG_PERM_WRITE | VM_MAP_REGION_FLAG_PERM_EXECUTE;
if (uncached) {
flags |= VM_MAP_REGION_FLAG_UNCACHED;
}
⑷ status = LOS_ArchMmuMap(&kSpace->archMmu, virtAddr, SYS_MEM_BASE,
(textStart - virtAddr) >> MMU_DESCRIPTOR_L2_SMALL_SHIFT,
flags);
if (status != ((textStart - virtAddr) >> MMU_DESCRIPTOR_L2_SMALL_SHIFT)) {
VM_ERR("mmap failed, status: %d", status);
return;
}
⑸ length = sizeof(mmuKernelMappings) / sizeof(LosArchMmuInitMapping);
for (i = 0; i < length; i++) {
kernelMap = &mmuKernelMappings[i];
if (uncached) {
kernelMap->flags |= VM_MAP_REGION_FLAG_UNCACHED;
}
status = LOS_ArchMmuMap(&kSpace->archMmu, kernelMap->virt, kernelMap->phys,
kernelMap->size >> MMU_DESCRIPTOR_L2_SMALL_SHIFT, kernelMap->flags);
if (status != (kernelMap->size >> MMU_DESCRIPTOR_L2_SMALL_SHIFT)) {
VM_ERR("mmap failed, status: %d", status);
return;
}
LOS_VmSpaceReserve(kSpace, kernelMap->size, kernelMap->virt);
}
⑹ kmallocLength = virtAddr + SYS_MEM_SIZE_DEFAULT - bssEndBoundary;
flags = VM_MAP_REGION_FLAG_PERM_READ | VM_MAP_REGION_FLAG_PERM_WRITE;
if (uncached) {
flags |= VM_MAP_REGION_FLAG_UNCACHED;
}
status = LOS_ArchMmuMap(&kSpace->archMmu, bssEndBoundary,
SYS_MEM_BASE + bssEndBoundary - virtAddr,
kmallocLength >> MMU_DESCRIPTOR_L2_SMALL_SHIFT,
flags);
if (status != (kmallocLength >> MMU_DESCRIPTOR_L2_SMALL_SHIFT)) {
VM_ERR("mmap failed, status: %d", status);
return;
}
LOS_VmSpaceReserve(kSpace, kmallocLength, bssEndBoundary);
}
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2.3 函数OsKSectionNewAttrEnable
函数OsKSectionNewAttrEnable
设置虚实地址的转换表基地址TTB并清楚TLB缓存。⑴处获取内核虚拟进程空间,⑵处设置进程空间MMU的虚拟地址转换表基地址TTB,然后查询到物理内存地址并设置物理内存地址转换表基地址。⑶处从CP15 C2寄存器读取TTB地址,取高20位。⑷处将内核物理内存页表基地址写入CP15 c2 TTB寄存器。⑸处清空TLB缓冲区,然后释放内存。涉及到了MMU寄存器,后续系列会专门详细讲解。
【#本文正在参与优质创作者激励#】
2.1 函数OsSwitchTmpTTB
这里应该这么描述合理一些:L1页表由4096个页表项组成,每个页表项占用4Bit,而不是4KB,否则4096*KB = 16MB了
感谢指正,已修改