Re: [PATCH v10 9/9] arm64: armv8_deprecated: apply FEAT_LSUI for swpX emulation.

[...]

+static __always_inline int +__lsui_user_swpb_asm(unsigned int *data, unsigned int addr) +{

• unsigned char idx;
• int err;
• unsigned int addr_al;
• union {

• unsigned int var;
  

• unsigned char raw[4];
  

• } data_al;
• idx = addr & (sizeof(unsigned int) - 1);
• addr_al = ALIGN_DOWN(addr, sizeof(unsigned int));
• if (get_user(data_al.var, (unsigned int *)(unsigned long)addr_al))

• return -EFAULT;
  

• data_al.raw[idx] = *data;
• err = __lsui_user_swp_asm(&data_al.var, addr_al);

I found that using swpt for swpb can cause a race condition when each CPU accesses its own dedicated byte memory region in 4 bytes. So, unless there are any comments, I’ll rework it with a cast in the next version.

• if (!err)

• *data = data_al.raw[idx];
  

• return err;

+} +#endif /* CONFIG_AS_HAS_LSUI */

Thanks.

-- Sincerely, Yeoreum Yun