Linux 内核 内存管理memblock 分配器 ⑤ ( Linux 内核中定义 memblock 分配器的位置 | ARM64体系架构下 Linux内核初始化 memblock 分配器流程 )

Posted 2022-04-21 韩曙亮

文章目录

• 一、Linux 内核中定义 memblock 分配器的位置
• 二、ARM64 体系架构下 Linux 内核初始化 memblock 分配器流程
• 三、arm64_memblock_init 函数完整源码

一、Linux 内核中定义 memblock 分配器的位置

---

Linux 内核 定义 memblock 分配器 位置 :

Linux 内核源码 linux-4.12\\mm\\memblock.c#34 位置 , 定义了 struct memblock 类型的变量 , 在该结构体赋值时 , .bottom_up = false 将 bottom_up 设置为了 false , 表示内存从 高地址向下分配 ;

struct memblock memblock __initdata_memblock = 
	.memory.regions		= memblock_memory_init_regions,
	.memory.cnt		= 1,	/* empty dummy entry */
	.memory.max		= INIT_MEMBLOCK_REGIONS,
	.memory.name		= "memory",

	.reserved.regions	= memblock_reserved_init_regions,
	.reserved.cnt		= 1,	/* empty dummy entry */
	.reserved.max		= INIT_MEMBLOCK_REGIONS,
	.reserved.name		= "reserved",

#ifdef CONFIG_HAVE_MEMBLOCK_PHYS_MAP
	.physmem.regions	= memblock_physmem_init_regions,
	.physmem.cnt		= 1,	/* empty dummy entry */
	.physmem.max		= INIT_PHYSMEM_REGIONS,
	.physmem.name		= "physmem",
#endif

	.bottom_up		= false,
	.current_limit		= MEMBLOCK_ALLOC_ANYWHERE,
;

源码路径 : linux-4.12\\mm\\memblock.c#34

二、ARM64 体系架构下 Linux 内核初始化 memblock 分配器流程

---

先在 linux-4.12\\init#488 位置的 asmlinkage __visible void __init start_kernel(void) 内核启动函数中 , 调用 setup_arch(&command_line); 函数 ,

然后再调用 ARM64 体系架构对应的源码 , linux-4.12\\arch\\arm64\\mm\\init.c#362 位置的 void __init arm64_memblock_init(void) 函数 , 该函数是 初始化 memblock 分配器的核心函数 ;

ARM64 体系架构下 Linux 内核初始化 memblock 分配器流程 :

① 解析 " 设备树二进制文件 " /memory 节点 , 将 " 所有物理内存 " 纳入到 memblock 分配器 管理之下 ;

该步骤对应的 Linux 源代码是在 linux-4.12\\arch\\arm64\\mm\\init.c#367 位置 ;

	/* Handle linux,usable-memory-range property */
	fdt_enforce_memory_region();

源码路径 : linux-4.12\\arch\\arm64\\mm\\init.c#367

② 设置 全局变量 memstart_addr , 用于记录 物理内存 的 起始地址 ;

	/*
	 * Select a suitable value for the base of physical memory.
	 */
	memstart_addr = round_down(memblock_start_of_DRAM(),
				   ARM64_MEMSTART_ALIGN);

源码路径 : linux-4.12\\arch\\arm64\\mm\\init.c#379

③ 从 memblock 分配器 中 , 删除 " 线性映射区域 不能覆盖的 指定范围的 物理内存 " ;

	/*
	 * Remove the memory that we will not be able to cover with the
	 * linear mapping. Take care not to clip the kernel which may be
	 * high in memory.
	 */
	memblock_remove(max_t(u64, memstart_addr + linear_region_size,
			__pa_symbol(_end)), ULLONG_MAX);

源码路径 : linux-4.12\\arch\\arm64\\mm\\init.c#387

④ 使用 mem 可以指定 " 设备树二进制文件中指定命令行 " 的 " 可用内存 " 大小 ,

如果指定了该可用内存大小 , 需要从 memblock 分配器 中 , 删除该大小之外超出的部分物理内存 ;

	/*
	 * Apply the memory limit if it was set. Since the kernel may be loaded
	 * high up in memory, add back the kernel region that must be accessible
	 * via the linear mapping.
	 */
	if (memory_limit != (phys_addr_t)ULLONG_MAX) 
		memblock_mem_limit_remove_map(memory_limit);
		memblock_add(__pa_symbol(_text), (u64)(_end - _text));
	

源码路径 : linux-4.12\\arch\\arm64\\mm\\init.c#401

⑤ 将 内核镜像 占用的 物理内存 纳入到 memblock 分配器 管理之下 ;

	/*
	 * Register the kernel text, kernel data, initrd, and initial
	 * pagetables with memblock.
	 */
	memblock_reserve(__pa_symbol(_text), _end - _text);

源码路径 : linux-4.12\\arch\\arm64\\mm\\init.c#456

⑥ 初始化 " 设备树二进制文件 " 内存区域 对应的 设备源文件相关字段和节点 ;

	early_init_fdt_scan_reserved_mem();

源码路径 : linux-4.12\\arch\\arm64\\mm\\init.c#467

三、arm64_memblock_init 函数完整源码

---

void __init arm64_memblock_init(void)

	const s64 linear_region_size = -(s64)PAGE_OFFSET;

	/* Handle linux,usable-memory-range property */
	fdt_enforce_memory_region();

	/*
	 * Ensure that the linear region takes up exactly half of the kernel
	 * virtual address space. This way, we can distinguish a linear address
	 * from a kernel/module/vmalloc address by testing a single bit.
	 */
	BUILD_BUG_ON(linear_region_size != BIT(VA_BITS - 1));

	/*
	 * Select a suitable value for the base of physical memory.
	 */
	memstart_addr = round_down(memblock_start_of_DRAM(),
				   ARM64_MEMSTART_ALIGN);

	/*
	 * Remove the memory that we will not be able to cover with the
	 * linear mapping. Take care not to clip the kernel which may be
	 * high in memory.
	 */
	memblock_remove(max_t(u64, memstart_addr + linear_region_size,
			__pa_symbol(_end)), ULLONG_MAX);
	if (memstart_addr + linear_region_size < memblock_end_of_DRAM()) 
		/* ensure that memstart_addr remains sufficiently aligned */
		memstart_addr = round_up(memblock_end_of_DRAM() - linear_region_size,
					 ARM64_MEMSTART_ALIGN);
		memblock_remove(0, memstart_addr);
	

	/*
	 * Apply the memory limit if it was set. Since the kernel may be loaded
	 * high up in memory, add back the kernel region that must be accessible
	 * via the linear mapping.
	 */
	if (memory_limit != (phys_addr_t)ULLONG_MAX) 
		memblock_mem_limit_remove_map(memory_limit);
		memblock_add(__pa_symbol(_text), (u64)(_end - _text));
	

	if (IS_ENABLED(CONFIG_BLK_DEV_INITRD) && initrd_start) 
		/*
		 * Add back the memory we just removed if it results in the
		 * initrd to become inaccessible via the linear mapping.
		 * Otherwise, this is a no-op
		 */
		u64 base = initrd_start & PAGE_MASK;
		u64 size = PAGE_ALIGN(initrd_end) - base;

		/*
		 * We can only add back the initrd memory if we don't end up
		 * with more memory than we can address via the linear mapping.
		 * It is up to the bootloader to position the kernel and the
		 * initrd reasonably close to each other (i.e., within 32 GB of
		 * each other) so that all granule/#levels combinations can
		 * always access both.
		 */
		if (WARN(base < memblock_start_of_DRAM() ||
			 base + size > memblock_start_of_DRAM() +
				       linear_region_size,
			"initrd not fully accessible via the linear mapping -- please check your bootloader ...\\n")) 
			initrd_start = 0;
		 else 
			memblock_remove(base, size); /* clear MEMBLOCK_ flags */
			memblock_add(base, size);
			memblock_reserve(base, size);
		
	

	if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) 
		extern u16 memstart_offset_seed;
		u64 range = linear_region_size -
			    (memblock_end_of_DRAM() - memblock_start_of_DRAM());

		/*
		 * If the size of the linear region exceeds, by a sufficient
		 * margin, the size of the region that the available physical
		 * memory spans, randomize the linear region as well.
		 */
		if (memstart_offset_seed > 0 && range >= ARM64_MEMSTART_ALIGN) 
			range = range / ARM64_MEMSTART_ALIGN + 1;
			memstart_addr -= ARM64_MEMSTART_ALIGN *
					 ((range * memstart_offset_seed) >> 16);
		
	

	/*
	 * Register the kernel text, kernel data, initrd, and initial
	 * pagetables with memblock.
	 */
	memblock_reserve(__pa_symbol(_text), _end - _text);
#ifdef CONFIG_BLK_DEV_INITRD
	if (initrd_start) 
		memblock_reserve(initrd_start, initrd_end - initrd_start);

		/* the generic initrd code expects virtual addresses */
		initrd_start = __phys_to_virt(initrd_start);
		initrd_end = __phys_to_virt(initrd_end);
	
#endif

	early_init_fdt_scan_reserved_mem();

	/* 4GB maximum for 32-bit only capable devices */
	if (IS_ENABLED(CONFIG_ZONE_DMA))
		arm64_dma_phys_limit = max_zone_dma_phys();
	else
		arm64_dma_phys_limit = PHYS_MASK + 1;

	reserve_crashkernel();

	reserve_elfcorehdr();

	dma_contiguous_reserve(arm64_dma_phys_limit);

	memblock_allow_resize();