cat /proc/cpuinfo里面有一项flags，每个flag都是什么意思呢？
fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall lm ...

这些flag可以从内核代码arch/x86/include/asm/cpufeature.h看到：
/* Intel-defined CPU features, CPUID level 0x00000001 (edx), word 0 */
#define X86_FEATURE_FPU (0*32+ 0) /* Onboard FPU */
#define X86_FEATURE_VME (0*32+ 1) /* Virtual Mode Extensions */
#define X86_FEATURE_DE (0*32+ 2) /* Debugging Extensions */
...
/* AMD-defined CPU features, CPUID level 0x80000001, word 1 */
/* Don't duplicate feature flags which are redundant with Intel! */
#define X86_FEATURE_SYSCALL (1*32+11) /* SYSCALL/SYSRET */
#define X86_FEATURE_MP (1*32+19) /* MP Capable. */
#define X86_FEATURE_NX (1*32+20) /* Execute Disable */
#define X86_FEATURE_MMXEXT (1*32+22) /* AMD MMX extensions */
#define X86_FEATURE_FXSR_OPT (1*32+25) /* FXSAVE/FXRSTOR optimizations */
#define X86_FEATURE_GBPAGES (1*32+26) /* "pdpe1gb" GB pages */
#define X86_FEATURE_RDTSCP (1*32+27) /* RDTSCP */
#define X86_FEATURE_LM (1*32+29) /* Long Mode (x86-64) */
#define X86_FEATURE_3DNOWEXT (1*32+30) /* AMD 3DNow! extensions */
#define X86_FEATURE_3DNOW (1*32+31) /* 3DNow! */
...

比如里面的flag lm，是指long mode，也就是x86_64，
address sizes : 40 bits physical, 48 bits virtual，
虽然是64位的，但是只用了48位的虚拟地址，40位的物理地址，该cpu支持的最大的物理内存是1T