ATF 页表构建代码分析_atf code分析

以mt8173为例 

/*******************************************************************************
 * Macro generating the code for the function setting up the pagetables as per
 * the platform memory map & initialize the mmu, for the given exception level
 ******************************************************************************/
#define DEFINE_CONFIGURE_MMU_EL(_el)					\
	void plat_configure_mmu_el ## _el(unsigned long total_base,	\
					  unsigned long total_size,	\
					  unsigned long ro_start,	\
					  unsigned long ro_limit,	\
					  unsigned long coh_start,	\
					  unsigned long coh_limit)	\
	{								\
		mmap_add_region(total_base, total_base,			\
				total_size,				\
				MT_MEMORY | MT_RW | MT_SECURE);		\
		mmap_add_region(ro_start, ro_start,			\
				ro_limit - ro_start,			\
				MT_MEMORY | MT_RO | MT_SECURE);		\
		mmap_add_region(coh_start, coh_start,			\
				coh_limit - coh_start,			\
				MT_DEVICE | MT_RW | MT_SECURE);		\
		mmap_add(plat_mmap);					\
		init_xlat_tables();					\
									\
		enable_mmu_el ## _el(0);				\
	}
 
/* Define EL3 variants of the function initialising the MMU */
DEFINE_CONFIGURE_MMU_EL(3)
 
DEFINE_ENABLE_MMU_EL(3,TCR_EL3_RES1 | (tcr_ps_bits << TCR_EL3_PS_SHIFT),tlbialle3) //定义el3 mmu函数

 mmap region 内存添加到系统中

void mmap_add_region(unsigned long base_pa, unsigned long base_va,
			unsigned long size, unsigned attr)
{
	mmap_region_t *mm = mmap;
	mmap_region_t *mm_last = mm + ARRAY_SIZE(mmap) - 1;
	unsigned long pa_end = base_pa + size - 1;
	unsigned long va_end = base_va + size - 1;
 
	assert(IS_PAGE_ALIGNED(base_pa));
	assert(IS_PAGE_ALIGNED(base_va));
	assert(IS_PAGE_ALIGNED(size));
 
	if (!size)
		return;
 
	/* Find correct place in mmap to insert new region */
	while (mm->base_va < base_va && mm->size)//从开始遍历，查看需要插入到哪个位置，base_va是需要插入的va
		++mm;
//mm->base_va >= base_va 则退出循环
	/* Make room for new region by moving other regions up by one place */
	memmove(mm + 1, mm, (uintptr_t)mm_last - (uintptr_t)mm);//从mm数组元素开始到最后，整体向后移动1个单位
 
	/* Check we haven't lost the empty sentinal from the end of the array */
	assert(mm_last->size == 0);
 
	mm->base_pa = base_pa;//insert new value
	mm->base_va = base_va;
	mm->size = size;
	mm->attr = attr;
 
	if (pa_end > max_pa)
		max_pa = pa_end;
	if (va_end > max_va)
		max_va = va_end;
}
 
void mmap_add(const mmap_region_t *mm)
{
	while (mm->size) {
		mmap_add_region(mm->base_pa, mm->base_va, mm->size, mm->attr);
		++mm;
	}
}

初始化页表，使用了递归操作

static mmap_region_t *init_xlation_table(mmap_region_t *mm,
					unsigned long base_va,
					unsigned long *table, unsigned level)
{
	unsigned level_size_shift = L1_XLAT_ADDRESS_SHIFT - (level - 1) *
						XLAT_TABLE_ENTRIES_SHIFT;
	unsigned level_size = 1 << level_size_shift;
	unsigned long level_index_mask = XLAT_TABLE_ENTRIES_MASK << level_size_shift;
 
	assert(level <= 3);
 
	debug_print("New xlat table:\n");
 
	do  {
		unsigned long desc = UNSET_DESC;//0xffffffff
 
		if (mm->base_va + mm->size <= base_va) {//若此时mm映射过了，跳入下一个mm,base_va一直在递增
			/* Area now after the region so skip it */
			++mm;
			continue;
		}
 
		debug_print("      %010lx %8lx " + 6 - 2 * level, base_va,
				level_size);
 
		if (mm->base_va >= base_va + level_size) {//说明在base_va的后面，先设置成invalid
			/* Next region is after area so nothing to map yet */
			desc = INVALID_DESC;
		} else if (mm->base_va <= base_va && mm->base_va + mm->size >=
				base_va + level_size) {//若需要映射区域可以覆盖此level一级大小，则不需要下一级
			/* Next region covers all of area */
			int attr = mmap_region_attr(mm, base_va, level_size);//获取映射属性
			if (attr >= 0)
				desc = mmap_desc(attr,
					base_va - mm->base_va + mm->base_pa,
					level);
		}
		/* else Next region only partially covers area, so need */
 
		if (desc == UNSET_DESC) {//其他情况都需要下一级页表，主要包括2M区域，mm的小于2M的区域则走这个地方
			/* Area not covered by a region so need finer table */
			unsigned long *new_table = xlat_tables[next_xlat++];
			assert(next_xlat <= MAX_XLAT_TABLES);
			desc = TABLE_DESC | (unsigned long)new_table;
 
			/* Recurse to fill in new table */
			mm = init_xlation_table(mm, base_va,
						new_table, level+1);//递归调用，填充下一级表格
		}
 
		debug_print("\n");
 
		*table++ = desc;//表描述符赋值
		base_va += level_size;// 虚拟地址增加
	} while (mm->size && (base_va & level_index_mask));//base_va & level_index_mask为0时结束递归代表则返回到向上一个level函数
 
	return mm;
}

使能mmu 重要寄存器（system register）配置代码

/*******************************************************************************
 * Macro generating the code for the function enabling the MMU in the given
 * exception level, assuming that the pagetables have already been created.
 *
 *   _el:		Exception level at which the function will run
 *   _tcr_extra:	Extra bits to set in the TCR register. This mask will
 *			be OR'ed with the default TCR value.
 *   _tlbi_fct:		Function to invalidate the TLBs at the current
 *			exception level
 ******************************************************************************/
#define DEFINE_ENABLE_MMU_EL(_el, _tcr_extra, _tlbi_fct)		\
	void enable_mmu_el##_el(uint32_t flags)				\
	{								\
		uint64_t mair, tcr, ttbr;				\
		uint32_t sctlr;						\
									\
		assert(IS_IN_EL(_el));					\
		assert((read_sctlr_el##_el() & SCTLR_M_BIT) == 0);	\
									\
		/* Set attributes in the right indices of the MAIR */	\
		mair = MAIR_ATTR_SET(ATTR_DEVICE, ATTR_DEVICE_INDEX);	\   //attr1
		mair |= MAIR_ATTR_SET(ATTR_IWBWA_OWBWA_NTR,		\
				ATTR_IWBWA_OWBWA_NTR_INDEX);		\  //attr0 inner writeback,write alloc,outer writeback,write alloc,
		write_mair_el##_el(mair);				\
									\
		/* Invalidate TLBs at the current exception level */	\
		_tlbi_fct();						\
									\
		/* Set TCR bits as well. */				\
		/* Inner & outer WBWA & shareable + T0SZ = 32 */	\
		tcr = TCR_SH_INNER_SHAREABLE | TCR_RGN_OUTER_WBA |	\
			TCR_RGN_INNER_WBA |				\
			(64 - __builtin_ctzl(ADDR_SPACE_SIZE));		\
		tcr |= _tcr_extra;					\
		write_tcr_el##_el(tcr);					\   //-----------tcr 写入
									\
		/* Set TTBR bits as well */				\
		ttbr = (uint64_t) l1_xlation_table;			\
		write_ttbr0_el##_el(ttbr);				\         //-----页表基地址写入
									\
		/* Ensure all translation table writes have drained */	\
		/* into memory, the TLB invalidation is complete, */	\
		/* and translation register writes are committed */	\
		/* before enabling the MMU */				\
		dsb();							\
		isb();							\
									\
		sctlr = read_sctlr_el##_el();				\
		sctlr |= SCTLR_WXN_BIT | SCTLR_M_BIT;			\
									\
		if (flags & DISABLE_DCACHE)				\
			sctlr &= ~SCTLR_C_BIT;				\
		else							\
			sctlr |= SCTLR_C_BIT;				\
									\
		write_sctlr_el##_el(sctlr);				\  //----------sctlr_el3写入
									\
		/* Ensure the MMU enable takes effect immediately */	\
		isb();							\
	}
 
/* Define EL1 and EL3 variants of the function enabling the MMU */
DEFINE_ENABLE_MMU_EL(1,(tcr_ps_bits << TCR_EL1_IPS_SHIFT),tlbivmalle1)  //定义el1 mmu函数
DEFINE_ENABLE_MMU_EL(3,TCR_EL3_RES1 | (tcr_ps_bits << TCR_EL3_PS_SHIFT),tlbialle3) //定义el3 mmu函数

重要的block or page 描述符赋值代码

static unsigned long mmap_desc(unsigned attr, unsigned long addr_pa,
					unsigned level)
{
	unsigned long desc = addr_pa;
 
	desc |= level == 3 ? TABLE_DESC : BLOCK_DESC;//bit[1:0]
 
	desc |= attr & MT_NS ? LOWER_ATTRS(NS) : 0; //NS, bit[5] 
 
	desc |= attr & MT_RW ? LOWER_ATTRS(AP_RW) : LOWER_ATTRS(AP_RO);//AP[2:1]---> bits[7:6] 
 
	desc |= LOWER_ATTRS(ACCESS_FLAG);//bit10
 
	if (attr & MT_MEMORY) {
		desc |= LOWER_ATTRS(ATTR_IWBWA_OWBWA_NTR_INDEX | ISH);//attr0@mair_el3
		if (attr & MT_RW)
			desc |= UPPER_ATTRS(XN);//读写区域不能执行指令 ，bit[54] xn
	} else {
		desc |= LOWER_ATTRS(ATTR_DEVICE_INDEX | OSH);//attr1@mair_el3，device memory outer shareable
		desc |= UPPER_ATTRS(XN);//no instruction execute
	}
 
	debug_print(attr & MT_MEMORY ? "MEM" : "DEV");
	debug_print(attr & MT_RW ? "-RW" : "-RO");
	debug_print(attr & MT_NS ? "-NS" : "-S");
 
	return desc;
}

代码调用总结如下图