Re: [RFC PATCH] asm/generic: introduce if_nospec and nospec_barrier

Linus Torvalds
2018-01-04T22:23:30Z

On Thu, Jan 4, 2018 at 2:20 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> #define array_access(base, idx, max) ({ \
> union { typeof(base[0]) _val; unsigned long _bit; } __u;\
> unsigned long _i = (idx); \
> unsigned long _m = (max); \
> unsigned long _mask = _i < _m ? ~0 : 0; \
> OPTIMIZER_HIDE_VAR(_mask); \
> __u._val = base[_i & _mask]; \
> __u._bit &= _mask; \
> __u._val; })

That

__u._val = base[_i & _mask];

thing would have to be READ_ONCE() to make it all ok for the special
cases without locking etc.

Linus