!3724 lib/clear_user: ensure loop in __arch_clear_user cache-aligned v2

Merge Pull Request from: @ci-robot 
 
PR sync from: Yang Yingliang <yangyingliang@huawei.com>
https://mailweb.openeuler.org/hyperkitty/list/kernel@openeuler.org/message/PW4CR3L42VTHR64ESRT3J5E2QAUFOWY6/ 
We must ensure that the following four instructions are cache-aligned.
Otherwise, it will cause problems with the performance of libMicro
pread.

```
1:
        # uao_user_alternative 9f, str, sttr, xzr, x0, 8
        str     xzr, [x0], #8
        nop
        subs    x1, x1, #8
        b.pl    1b

with this patch:

             prc thr   usecs/call      samples   errors cnt/samp     size
pread_z100     1   1      5.88400          807        0 1            102400
```

The result of pread can range from 5 to 9 depending on  the
alignment performance of this function.

Cheng Jian (1):
  lib/clear_user: ensure loop in __arch_clear_user cache-aligned v2

Yang Yingliang (1):
  config: enable CONFIG_CLEAR_USER_WORKAROUND by default


-- 
2.25.1
 
https://gitee.com/openeuler/kernel/issues/I8T1T8 
 
Link:https://gitee.com/openeuler/kernel/pulls/3724

 

Reviewed-by: Zhang Jianhua <chris.zjh@huawei.com>
Reviewed-by: Liu Chao <liuchao173@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>