转自：http://blog.csdn.net/boymax2/article/details/52550197
版权声明：本文为博主原创文章，未经博主允许不得转载。
Magenta内核支持虚拟地址的配置，依赖于cpu内的mmu模块。
下面会从以下几个方面对Magenta内核内存管理方面的代码进行分析：
1、mmu初始化，也就是硬件mmu的初始化，以底层寄存器操作为主，汇编
2、pmm初始化，也就是代码中物理内存结构的初始化
3、vmm初始化，也就是代码中虚拟内存结构的初始化
mmu初始化
mmu初始化的代码由汇编完成，其中主要涉及了以下几个结构
TLB：内存映射表，其定义位于c代码中
kernel/arch/arm/arm/mmu.c
[cpp] view plain copy
uint32_t arm_kernel_translation_table[TT_ENTRY_COUNT] __ALIGNED(16384) __SECTION(".bss.prebss.translation_table");
以及初始化的内存映射关系，以qemu-virt平台
kernel/platform/qemu-virt/platform.c
[cpp] view plain copy
struct mmu_initial_mapping mmu_initial_mappings[] = {
/* all of memory */
{
.phys = MEMORY_BASE_PHYS, // 内存物理基地址
.virt = KERNEL_BASE, // 内存虚拟基地址
.size = MEMORY_APERTURE_SIZE,// 虚拟内存大小
.flags = 0,
.name = "memory"
},
/* 1GB of peripherals */
{
.phys = PERIPHERAL_BASE_PHYS, // 外设物理基地址
.virt = PERIPHERAL_BASE_VIRT, // 外设虚拟基地址
.size = PERIPHERAL_BASE_SIZE, // 虚拟内存大小
.flags = MMU_INITIAL_MAPPING_FLAG_DEVICE,
.name = "peripherals"
},
/* null entry to terminate the list */
{ 0 }
};
这两个结构都会在之后的汇编代码中使用。
mmu初始化的汇编代码位于内核的启动文件中，以arm32为例
自己对arm汇编不是很熟悉，在读汇编代码时花费了比较多的时间，希望有错误能指正出来
启动文件中与mmu相关的代码已经提取出来
在其中主要涉及到的操作为以下几个：
1、重置mmu相关寄存器
2、计算物理地址相对虚拟地址的偏移
3、将tlb地址指向空间清零
4、遍历mmu_initial_mappings结构，计算后写入tlb
5、设置mmu相关寄存器
6、跳转至c代码
kernel/arch/arm/arm/start.S
[plain] view plain copy
#include <asm.h>
#include <arch/arm/cores.h>
#include <arch/arm/mmu.h>
#include <kernel/vm.h>
.section ".text.boot"
.globl _start
_start:
b platform_reset
b arm_undefined
b arm_syscall
b arm_prefetch_abort
b arm_data_abort
b arm_reserved
b arm_irq
b arm_fiq
#if WITH_SMP
b arm_reset
#endif
.weak platform_reset
platform_reset:
/* Fall through for the weak symbol */
// arm复位处理程序
.globl arm_reset
arm_reset:
/* do some early cpu setup */
// 读SCTLR寄存器，手册P1711
mrc p15, 0, r12, c1, c0, 0
/* i/d cache disable, mmu disabled */
// cache位与mmu位置0
bic r12, #(1<<12)
bic r12, #(1<<2 | 1<<0)
#if WITH_KERNEL_VM
/* enable caches so atomics and spinlocks work */
// cache位与mmu位置1
orr r12, r12, #(1<<12)
orr r12, r12, #(1<<2)
#endif // WITH_KERNEL_VM
// 写SCTLR寄存器
mcr p15, 0, r12, c1, c0, 0
/* calculate the physical offset from our eventual virtual location */
// 计算物理地址相对虚拟地址的偏移，用于之后的转换
.Lphys_offset:
ldr r4, =.Lphys_offset
adr r11, .Lphys_offset
sub r11, r11, r4
...
#if ARM_WITH_MMU
.Lsetup_mmu:
/* set up the mmu according to mmu_initial_mappings */
/* load the base of the translation table and clear the table */
// 获取转换表地址
ldr r4, =arm_kernel_translation_table
// 获取转换表物理地址
add r4, r4, r11
/* r4 = physical address of translation table */
mov r5, #0
mov r6, #0
/* walk through all the entries in the translation table, setting them up */
// 遍历转换表结构清零
0:
str r5, [r4, r6, lsl #2]
add r6, #1
cmp r6, #4096
bne 0b
/* load the address of the mmu_initial_mappings table and start processing */
// 获取初始映射地址
ldr r5, =mmu_initial_mappings
// 获取初始映射物理地址
add r5, r5, r11
/* r5 = physical address of mmu initial mapping table */
// 初始映射遍历绑定至转换表
// 转换表的绑定 转换表中元素的高12位为物理基地址下标，低20位为mmu相关flag
.Linitial_mapping_loop:
// 把结构体加载到各个通用寄存器中
ldmia r5!, { r6-r10 }
/* r6 = phys, r7 = virt, r8 = size, r9 = flags, r10 = name */
/* round size up to 1MB alignment */
// 上调size对齐1MB
ubfx r10, r6, #0, #20
add r8, r8, r10
add r8, r8, #(1 << 20)
sub r8, r8, #1
/* mask all the addresses and sizes to 1MB boundaries */
// 物理地址 虚拟地址 大小 右移20位 取高12位
lsr r6, #20 /* r6 = physical address / 1MB */
lsr r7, #20 /* r7 = virtual address / 1MB */
lsr r8, #20 /* r8 = size in 1MB chunks */
/* if size == 0, end of list */
// 循环边界判断
cmp r8, #0
beq .Linitial_mapping_done
/* set up the flags */
// 设置mmu相关flag，放置在r10
ldr r10, =MMU_KERNEL_L1_PTE_FLAGS
teq r9, #MMU_INITIAL_MAPPING_FLAG_UNCACHED
ldreq r10, =MMU_INITIAL_MAP_STRONGLY_ORDERED
beq 0f
teq r9, #MMU_INITIAL_MAPPING_FLAG_DEVICE
ldreq r10, =MMU_INITIAL_MAP_DEVICE
/* r10 = mmu entry flags */
0:
// 计算translation_table元素的值
// r10：mmu相关flag r6：物理地址高12位
// r12 = r10 | (r6 << 20)
// 高20位为物理地址，低12位为mmu相关flag
orr r12, r10, r6, lsl #20
/* r12 = phys addr | flags */
/* store into appropriate translation table entry */
// r4：转换表物理基地址 r7：虚拟地址对应的section
// r12 -> [r4 + r7 << 2]
str r12, [r4, r7, lsl #2]
/* loop until we‘re done */
// 准备下一个转换表元素的填充
add r6, #1
add r7, #1
subs r8, #1
bne 0b
b .Linitial_mapping_loop
.Linitial_mapping_done:
...
/* set up the mmu */
bl .Lmmu_setup
#endif // WITH_KERNEL_VM
...
// 跳转至c程序
bl lk_main
b .
#if WITH_KERNEL_VM
/* per cpu mmu setup, shared between primary and secondary cpus
args:
r4 == translation table physical
r8 == final translation table physical (if using trampoline)
*/
// 设置mmu相关寄存器
// r4：转换表物理基地址
// mmu相关寄存器 手册P1724
.Lmmu_setup:
/* Invalidate TLB */
mov r12, #0
mcr p15, 0, r12, c8, c7, 0
isb
/* Write 0 to TTBCR */
// ttbcr写0
mcr p15, 0, r12, c2, c0, 2
isb
/* Set cacheable attributes on translation walk */
// 宏MMU_TTBRx_FLAGS为 (1 << 3) | (1 << 6)
orr r12, r4, #MMU_TTBRx_FLAGS
/* Write ttbr with phys addr of the translation table */
// 写入ttbr0
mcr p15, 0, r12, c2, c0, 0
isb
/* Write DACR */
// 写DACR cache相关
mov r12, #0x1
mcr p15, 0, r12, c3, c0, 0
isb
/* Read SCTLR into r12 */
// 读SCTLR寄存器，手册P1711
mrc p15, 0, r12, c1, c0, 0
/* Disable TRE/AFE */
// 禁用TRE和AFE标志位
bic r12, #(1<<29 | 1<<28)
/* Turn on the MMU */
// MMU使能标志位
orr r12, #0x1
/* Write back SCTLR */
// 写入SCTLR
// MMU打开
mcr p15, 0, r12, c1, c0, 0
isb
/* Jump to virtual code address */
// 跳转
ldr pc, =1f
1:
...
/* Invalidate TLB */
mov r12, #0
mcr p15, 0, r12, c8, c7, 0
isb
/* assume lr was in physical memory, adjust it before returning */
// 计算跳转点的虚拟地址，跳转，之后会调用lk_main
sub lr, r11
bx lr
#endif
...
硬件层的内存管理相关的初始化基本完成后，会跳转到c代码
位于kernel/top/main.c
其中有关内存管理的函数调用顺序为：
1、pmm_add_arena 将物理内存加入pmm结构
2、vm_init_preheap 堆初始化前的准备工作（钩子）
3、heap_init 堆的初始化
4、vm_init_postheap 堆初始化后的工作（钩子）
5、arm_mmu_init mmu相关的调整
首先要完成pmm初始化工作
pmm初始化主要分为以下几步：
1、通过fdt库从bootloader中获取物理内存的长度
2、在pmm中加入物理内存
3、标记fdt结构的空间
4、标记bootloader相关的空间
pmm中比较重要的一个结构体，pmm_arena_t代表着一块物理内存的抽象
kernel/include/kernel/vm.h
[cpp] view plain copy
typedef struct pmm_arena {
struct list_node node; // 节点，物理内存链表
const char* name; // 名称
uint flags;
uint priority;
paddr_t base; // 物理内存基地址
size_t size; // 物理内存长度
size_t free_count; // 空闲的页数
struct vm_page* page_array; // 页结构数组
struct list_node free_list; // 节点，该内存中空闲空间的链表
} pmm_arena_t;
接着以qemu-virt的platform为例，分析pmm初始化的过程
kernel/platform/qemu-virt.c
[cpp] view plain copy
// 全局物理内存结构体
static pmm_arena_t arena = {
.name = "ram",
.base = MEMORY_BASE_PHYS,
.size = DEFAULT_MEMORY_SIZE,
.flags = PMM_ARENA_FLAG_KMAP,
};
...
// 该函数为平台的早期初始化，在内核启动时调用
void platform_early_init(void)
{
...
/* look for a flattened device tree just before the kernel */
// 获取fdt结构
const void *fdt = (void *)KERNEL_BASE;
int err = fdt_check_header(fdt);
if (err >= 0) {
/* walk the nodes, looking for ‘memory‘ and ‘chosen‘ */
int depth = 0;
int offset = 0;
for (;;) {
offset = fdt_next_node(fdt, offset, &depth);
if (offset < 0)
break;
/* get the name */
const char *name = fdt_get_name(fdt, offset, NULL);
if (!name)
continue;
/* look for the properties we care about */
// 从fdt中查找到内存信息
if (strcmp(name, "memory") == 0) {
int lenp;
const void *prop_ptr = fdt_getprop(fdt, offset, "reg", &lenp);
if (prop_ptr && lenp == 0x10) {
/* we‘re looking at a memory descriptor */
//uint64_t base = fdt64_to_cpu(*(uint64_t *)prop_ptr);
// 获取内存长度
uint64_t len = fdt64_to_cpu(*((const uint64_t *)prop_ptr + 1));
/* trim size on certain platforms */
#if ARCH_ARM
// 如果是32位arm，只使用内存前1GB
if (len > 1024*1024*1024U) {
len = 1024*1024*1024; /* only use the first 1GB on ARM32 */
printf("trimming memory to 1GB\n");
}
#endif
/* set the size in the pmm arena */
// 保存内存长度
arena.size = len;
}
} else if (strcmp(name, "chosen") == 0) {
...
}
}
}
/* add the main memory arena */
// 将改内存区域加入到pmm中
pmm_add_arena(&arena);
/* reserve the first 64k of ram, which should be holding the fdt */
// 标记fdt区域
pmm_alloc_range(MEMBASE, 0x10000 / PAGE_SIZE, NULL);
// 标记bootloader_ramdisk区域
platform_preserve_ramdisk();
...
}
内核在接下来初始化堆之前会在内存中构造出出一个VmAspace对象，其代表的是内核空间的抽象
kernel/kernel/vm/vm.cpp
[cpp] view plain copy
void vm_init_preheap(uint level) {
LTRACE_ENTRY;
// allow the vmm a shot at initializing some of its data structures
// 构造代表内核空间的VmAspace对象
VmAspace::KernelAspaceInitPreHeap();
// mark all of the kernel pages in use
LTRACEF("marking all kernel pages as used\n");
// 标记内核代码所用内存
mark_pages_in_use((vaddr_t)&_start, ((uintptr_t)&_end - (uintptr_t)&_start));
// mark the physical pages used by the boot time allocator
// 标记boot time allocator代码所用内存
if (boot_alloc_end != boot_alloc_start) {
LTRACEF("marking boot alloc used from 0x%lx to 0x%lx\n", boot_alloc_start, boot_alloc_end);
mark_pages_in_use(boot_alloc_start, boot_alloc_end - boot_alloc_start);
}
}
kernel/kernel/vm/vm_aspace.cpp
[cpp] view plain copy
void VmAspace::KernelAspaceInitPreHeap() {
// the singleton kernel address space
// 构造一个内核空间单例，因为这个函数只会在启动时调用，所以是这个对象是单例
static VmAspace _kernel_aspace(KERNEL_ASPACE_BASE, KERNEL_ASPACE_SIZE, VmAspace::TYPE_KERNEL,
"kernel");
// 初始化
auto err = _kernel_aspace.Init();
ASSERT(err >= 0);
// save a pointer to the singleton kernel address space
// 保存单例指针
VmAspace::kernel_aspace_ = &_kernel_aspace;
}
VmAspace::VmAspace(vaddr_t base, size_t size, uint32_t flags, const char* name)
: base_(base), size_(size), flags_(flags) {
DEBUG_ASSERT(size != 0);
DEBUG_ASSERT(base + size - 1 >= base);
Rename(name);
LTRACEF("%p ‘%s‘\n", this, name_);
}
status_t VmAspace::Init() {
DEBUG_ASSERT(magic_ == MAGIC);
LTRACEF("%p ‘%s‘\n", this, name_);
// intialize the architectually specific part
// 标记为内核的空间
bool is_high_kernel = (flags_ & TYPE_MASK) == TYPE_KERNEL;
uint arch_aspace_flags = is_high_kernel ? ARCH_ASPACE_FLAG_KERNEL : 0;
// 调用mmu相关的函数
return arch_mmu_init_aspace(&arch_aspace_, base_, size_, arch_aspace_flags);
}
kernel/arch/arm/arm/mmu.c
[cpp] view plain copy
status_t arch_mmu_init_aspace(arch_aspace_t *aspace, vaddr_t base, size_t size, uint flags)
{
LTRACEF("aspace %p, base 0x%lx, size 0x%zx, flags 0x%x\n", aspace, base, size, flags);
DEBUG_ASSERT(aspace);
DEBUG_ASSERT(aspace->magic != ARCH_ASPACE_MAGIC);
/* validate that the base + size is sane and doesn‘t wrap */
DEBUG_ASSERT(size > PAGE_SIZE);
DEBUG_ASSERT(base + size - 1 > base);
// 初始化内核空间中页的链表
list_initialize(&aspace->pt_page_list);
aspace->magic = ARCH_ASPACE_MAGIC;
if (flags & ARCH_ASPACE_FLAG_KERNEL) {
// 设置结构内相关参数，其中转换表的物理内存通过vaddr_to_paddr获取
// 该函数不详细分析了，实质就是通过转换表进行查询得到的物理地址
aspace->base = base;
aspace->size = size;
aspace->tt_virt = arm_kernel_translation_table;
aspace->tt_phys = vaddr_to_paddr(aspace->tt_virt);
} else {
...
}
LTRACEF("tt_phys 0x%lx tt_virt %p\n", aspace->tt_phys, aspace->tt_virt);
return NO_ERROR;
}
到此内核空间的结构初始化完成
接下来进行内核堆的初始化，Magenta内核中提供了两种堆的实现miniheap以及cmpctmalloc，用户可以自己进行配置。
堆的具体实现方法会在之后进行具体的分析
堆的初始化完成以后，会调用相应的钩子函数，该函数的主要的作用如下：
1、在vmm结构中标记内核已使用的虚拟地址
2、根据内核使用的地址的区域，分别设置内存的保护
[cpp] view plain copy
void vm_init_postheap(uint level) {
LTRACE_ENTRY;
vmm_aspace_t* aspace = vmm_get_kernel_aspace();
// we expect the kernel to be in a temporary mapping, define permanent
// regions for those now
struct temp_region {
const char* name;
vaddr_t base;
size_t size;
uint arch_mmu_flags;
} regions[] = {
{
.name = "kernel_code",
.base = (vaddr_t)&__code_start,
.size = ROUNDUP((size_t)&__code_end - (size_t)&__code_start, PAGE_SIZE),
.arch_mmu_flags = ARCH_MMU_FLAG_PERM_READ | ARCH_MMU_FLAG_PERM_EXECUTE,
},
{
.name = "kernel_rodata",
.base = (vaddr_t)&__rodata_start,
.size = ROUNDUP((size_t)&__rodata_end - (size_t)&__rodata_start, PAGE_SIZE),
.arch_mmu_flags = ARCH_MMU_FLAG_PERM_READ,
},
{
.name = "kernel_data",
.base = (vaddr_t)&__data_start,
.size = ROUNDUP((size_t)&__data_end - (size_t)&__data_start, PAGE_SIZE),
.arch_mmu_flags = ARCH_MMU_FLAG_PERM_READ | ARCH_MMU_FLAG_PERM_WRITE,
},
{
.name = "kernel_bss",
.base = (vaddr_t)&__bss_start,
.size = ROUNDUP((size_t)&__bss_end - (size_t)&__bss_start, PAGE_SIZE),
.arch_mmu_flags = ARCH_MMU_FLAG_PERM_READ | ARCH_MMU_FLAG_PERM_WRITE,
},
{
.name = "kernel_bootalloc",
.base = (vaddr_t)boot_alloc_start,
.size = ROUNDUP(boot_alloc_end - boot_alloc_start, PAGE_SIZE),
.arch_mmu_flags = ARCH_MMU_FLAG_PERM_READ | ARCH_MMU_FLAG_PERM_WRITE,
},
};
for (uint i = 0; i < countof(regions); ++i) {
temp_region* region = ®ions[i];
ASSERT(IS_PAGE_ALIGNED(region->base));
status_t status = vmm_reserve_space(aspace, region->name, region->size, region->base);
ASSERT(status == NO_ERROR);
status = vmm_protect_region(aspace, region->base, region->arch_mmu_flags);
ASSERT(status == NO_ERROR);
}
// mmu_initial_mappings should reflect where we are now, use it to construct the actual
// mappings. We will carve out the kernel code/data from any mappings and
// unmap any temporary ones.
const struct mmu_initial_mapping* map = mmu_initial_mappings;
for (map = mmu_initial_mappings; map->size > 0; ++map) {
LTRACEF("looking at mapping %p (%s)\n", map, map->name);
// Unmap temporary mappings except where they intersect with the
// kernel code/data regions.
vaddr_t vaddr = map->virt;
LTRACEF("vaddr 0x%lx, virt + size 0x%lx\n", vaddr, map->virt + map->size);
while (vaddr != map->virt + map->size) {
vaddr_t next_kernel_region = map->virt + map->size;
vaddr_t next_kernel_region_end = map->virt + map->size;
// Find the kernel code/data region with the lowest start address
// that is within this mapping.
for (uint i = 0; i < countof(regions); ++i) {
temp_region* region = ®ions[i];
if (region->base >= vaddr && region->base < map->virt + map->size &&
region->base < next_kernel_region) {
next_kernel_region = region->base;
next_kernel_region_end = region->base + region->size;
}
}
// If vaddr isn‘t the start of a kernel code/data region, then we should make
// a mapping between it and the next closest one.
if (next_kernel_region != vaddr) {
status_t status =
vmm_reserve_space(aspace, map->name, next_kernel_region - vaddr, vaddr);
ASSERT(status == NO_ERROR);
if (map->flags & MMU_INITIAL_MAPPING_TEMPORARY) {
// If the region is part of a temporary mapping, immediately unmap it
LTRACEF("Freeing region [%016lx, %016lx)\n", vaddr, next_kernel_region);
status = vmm_free_region(aspace, vaddr);
ASSERT(status == NO_ERROR);
} else {
// Otherwise, mark it no-exec since it‘s not explicitly code
status = vmm_protect_region(
aspace,
vaddr,
ARCH_MMU_FLAG_PERM_READ | ARCH_MMU_FLAG_PERM_WRITE);
ASSERT(status == NO_ERROR);
}
}
vaddr = next_kernel_region_end;
}
}
}
以上代码中涉及到的几个函数，只是做下简单的介绍，不具体分析：
vmm_reserve_space：在vmm中标记一块虚拟内存，这块虚拟内存抽象为VmRegion类，拥有自己的底层mmu相关的配置
vmm_protect_region：对某VmRegion对应的虚拟内存设置内存保护的相关参数
mmu相关的调整
mmu相关的调整，由内核新建的bootstrap2线程进行调用arch_init完成
kernel/arch/arm/arm/arch.c
[cpp] view plain copy
void arch_init(void)
{
...
#if ARM_WITH_MMU
/* finish intializing the mmu */
arm_mmu_init();
#endif
}
kernel/arch/arm/arm/mmu.c
[cpp] view plain copy
void arm_mmu_init(void)
{
/* unmap the initial mapings that are marked temporary */
// 解除具有MMU_INITIAL_MAPPING_TEMPORARY标志的内存映射
struct mmu_initial_mapping *map = mmu_initial_mappings;
while (map->size > 0) {
if (map->flags & MMU_INITIAL_MAPPING_TEMPORARY) {
vaddr_t va = map->virt;
size_t size = map->size;
DEBUG_ASSERT(IS_SECTION_ALIGNED(size));
while (size > 0) {
arm_mmu_unmap_l1_entry(arm_kernel_translation_table, va / SECTION_SIZE);
va += MB;
size -= MB;
}
}
map++;
}
arm_after_invalidate_tlb_barrier();
#if KERNEL_ASPACE_BASE != 0
/* bounce the ttbr over to ttbr1 and leave 0 unmapped */
// 重新设置mmu相关的寄存器，禁用ttbcr0，将原先ttbr0的映射移动到ttbr1
// ttbr1为内核空间使用的寄存器
uint32_t n = __builtin_clz(KERNEL_ASPACE_BASE) + 1;
DEBUG_ASSERT(n <= 7);
uint32_t ttbcr = (1<<4) | n; /* disable TTBCR0 and set the split between TTBR0 and TTBR1 */
arm_write_ttbr1(arm_read_ttbr0());
ISB;
arm_write_ttbcr(ttbcr);
ISB;
arm_write_ttbr0(0);
ISB;
#endif
}
至此Magenta内核有关内存管理的初始化完成。
时间： 2024-08-01 20:36:44