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cpu_cache_init与rixi

cpu_cache_init接口:

  • 初始化cache(r4k_cache_init)
  • 设置cache的保护权限(setup_protection_map)
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kernel_start
\->setup_arch
\->cpu_cache_init()

file: arch/mips/mm/cache.c

r4k_cache_init

setup_protection_map

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static inline void setup_protection_map(void)
{
if (cpu_has_rixi) {
protection_map[0] = __pgprot(_page_cachable_default | _PAGE_PRESENT | _PAGE_NO_EXEC | _PAGE_NO_READ);
protection_map[1] = __pgprot(_page_cachable_default | _PAGE_PRESENT | _PAGE_NO_EXEC);
protection_map[2] = __pgprot(_page_cachable_default | _PAGE_PRESENT | _PAGE_NO_EXEC | _PAGE_NO_READ);
protection_map[3] = __pgprot(_page_cachable_default | _PAGE_PRESENT | _PAGE_NO_EXEC);
protection_map[4] = __pgprot(_page_cachable_default | _PAGE_PRESENT | _PAGE_NO_READ);
protection_map[5] = __pgprot(_page_cachable_default | _PAGE_PRESENT);
protection_map[6] = __pgprot(_page_cachable_default | _PAGE_PRESENT | _PAGE_NO_READ);
protection_map[7] = __pgprot(_page_cachable_default | _PAGE_PRESENT);

protection_map[8] = __pgprot(_page_cachable_default | _PAGE_PRESENT | _PAGE_NO_EXEC | _PAGE_NO_READ);
protection_map[9] = __pgprot(_page_cachable_default | _PAGE_PRESENT | _PAGE_NO_EXEC);
protection_map[10] = __pgprot(_page_cachable_default | _PAGE_PRESENT | _PAGE_NO_EXEC | _PAGE_WRITE | _PAGE_NO_READ);
protection_map[11] = __pgprot(_page_cachable_default | _PAGE_PRESENT | _PAGE_NO_EXEC | _PAGE_WRITE);
protection_map[12] = __pgprot(_page_cachable_default | _PAGE_PRESENT | _PAGE_NO_READ);
protection_map[13] = __pgprot(_page_cachable_default | _PAGE_PRESENT);
protection_map[14] = __pgprot(_page_cachable_default | _PAGE_PRESENT | _PAGE_WRITE | _PAGE_NO_READ);
protection_map[15] = __pgprot(_page_cachable_default | _PAGE_PRESENT | _PAGE_WRITE);

} else {
protection_map[0] = PAGE_NONE;
protection_map[1] = PAGE_READONLY;
protection_map[2] = PAGE_COPY;
protection_map[3] = PAGE_COPY;
protection_map[4] = PAGE_READONLY;
protection_map[5] = PAGE_READONLY;
protection_map[6] = PAGE_COPY;
protection_map[7] = PAGE_COPY;
protection_map[8] = PAGE_NONE;
protection_map[9] = PAGE_READONLY;
protection_map[10] = PAGE_SHARED;
protection_map[11] = PAGE_SHARED;
protection_map[12] = PAGE_READONLY;
protection_map[13] = PAGE_READONLY;
protection_map[14] = PAGE_SHARED;
protection_map[15] = PAGE_SHARED;
}
}

setup_protection_map函数主要是对protection_map结构体数组的初始化
cpu_has_rixi: 需要CPU中rixi的硬件支持

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/* description of effects of mapping type and prot in current implementation.
* this is due to the limited x86 page protection hardware. The expected
* behavior is in parens:
*
* map_type prot
* PROT_NONE PROT_READ PROT_WRITE PROT_EXEC
* MAP_SHARED r: (no) no r: (yes) yes r: (no) yes r: (no) yes
* w: (no) no w: (no) no w: (yes) yes w: (no) no
* x: (no) no x: (no) yes x: (no) yes x: (yes) yes
*
* MAP_PRIVATE r: (no) no r: (yes) yes r: (no) yes r: (no) yes
* w: (no) no w: (no) no w: (copy) copy w: (no) no
* x: (no) no x: (no) yes x: (no) yes x: (yes) yes
*
*/
pgprot_t protection_map[16] = {
__P000, __P001, __P010, __P011, __P100, __P101, __P110, __P111,
__S000, __S001, __S010, __S011, __S100, __S101, __S110, __S111
};

file: mm/mmap.c

protection_map定义16种内存访问权限,其中映射类型MAP_PRIVATEMAP_SHARED

__P000 的意思是 P ( private),0 ( No Exec),0 ( No Write),0 ( No Read);

__P001 的意思是 P ( private),0 ( No Exec),0 ( No Write),0 ( Read);

__S111 的意思是 S ( Shared),1 (Exec),1 ( Write),1 ( Read);

rixi

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#define cpu_has_rixi                    1

arch/mips/xburst2/soc-x2000/include/cpu-feature-overrides.h

使能该功能

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__pgprot(_page_cachable_default | _PAGE_PRESENT | _PAGE_NO_EXEC | _PAGE_NO_READ);

相应宏定义:

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#if defined(CONFIG_JZRISC_PEP) && defined(CONFIG_CPU_MIPS32)
#define _PAGE_PRESENT_SHIFT 0
#define _PAGE_PRESENT (1 << _PAGE_PRESENT_SHIFT)
#define _PAGE_READ_SHIFT 1
#define _PAGE_READ (1 << _PAGE_READ_SHIFT)
#define _PAGE_WRITE_SHIFT 2
#define _PAGE_WRITE (1 << _PAGE_WRITE_SHIFT)
#define _PAGE_ACCESSED_SHIFT 3
#define _PAGE_ACCESSED (1 << _PAGE_ACCESSED_SHIFT)
#define _PAGE_MODIFIED_SHIFT 4
#define _PAGE_MODIFIED (1 << _PAGE_MODIFIED_SHIFT)
#define _PAGE_FILE (1 << 4)
#define _PAGE_NO_EXEC (1 << 5)
#define _PAGE_GLOBAL (1 << 6)
#define _PAGE_VALID_SHIFT 7
#define _PAGE_VALID (1 << _PAGE_VALID_SHIFT)
#define _PAGE_SILENT_READ (1 << 7)
#define _PAGE_DIRTY_SHIFT 8
#define _PAGE_DIRTY (1 << _PAGE_DIRTY_SHIFT)
#define _PAGE_SILENT_WRITE (1 << 8)
#define _CACHE_SHIFT (9)
#define _CACHE_MASK (7 << _CACHE_SHIFT)
#define _PFN_SHIFT (PAGE_SHIFT - 12 + _CACHE_SHIFT + 3)

file: arch/mips/include/asm/pgtable-bits.h

_page_cachable_default

定义MMU的类型

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static void __cpuinit coherency_setup(void)
{
if (mips_cca < 0 || mips_cca > 7)
mips_cca = read_c0_config() & CONF_CM_CMASK;
_page_cachable_default = mips_cca << _CACHE_SHIFT;
...
}

file: arch/mips/mm/c-r4k.c

c0_config: Config寄存器主要描述CPU资源信息和配置,CONF_CM_CMASK(#define CONF_CM_CMASK 7)Config[7:9]为MT,表示MMU的类型

Config[7:9]: MT MMU类型

0: None; 1: MIPS32/64标准的TLB; 2:BAT类型; 3: MIPS32标准的FMT固定映射

cpu_has_rixi = 1 和 cpu_has_rixi = 0 区别

  • cpu_has_rixi = 1

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    protection_map[0]  = __pgprot(_page_cachable_default | _PAGE_PRESENT | _PAGE_NO_EXEC | _PAGE_NO_READ);
  • cpu_has_rixi = 0

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    #define _CACHE_CACHABLE_NONCOHERENT (3<<_CACHE_SHIFT)  /* R4[0246]00      */
    #define PAGE_NONE __pgprot(_PAGE_PRESENT | _CACHE_CACHABLE_NONCOHERENT)

    protection_map[0] = PAGE_NONE;

通过对protection_map[0]定义的对比,在使能rixi后,其属性增加了 _PAGE_NO_EXEC_PAGE_NO_READ
也就是rixi在内存的访问权限上增加了_PAGE_WRITE, _PAGE_READ,_PAGE_NO_READ, _PAGE_NO_EXEC的属性控制

参考

  1. 内核初始化
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