来自公众号：OSC开源社区
链接：https://www.oschina.net/news/318635/linus-2-6p-faster-scale-patch
“64 位 copy_from_user () 中的 barrier_nospec () 函数运行速度很慢。
如果地址无效，可以使用 pointer masking 来强制用户指针全为 1。”
#else#define can_do_masked_user_access() 0#define masked_user_access_begin(src) NULL+ #define mask_user_address(src) (src)#endif/*@@ -159,19 +160,27 @@ _inline_copy_from_user(void *to, const void __user *from, unsigned long n){unsigned long res = n;might_fault();- if (!should_fail_usercopy() && likely(access_ok(from, n))) {+ if (should_fail_usercopy())+ goto fail;+ if (can_do_masked_user_access())+ from = mask_user_address(from);+ else {+ if (!access_ok(from, n))+ goto fail;/** Ensure that bad access_ok() speculation will not* lead to nasty side effects *after* the copy is* finished:*/barrier_nospec();- instrument_copy_from_user_before(to, from, n);- res = raw_copy_from_user(to, from, n);- instrument_copy_from_user_after(to, from, n, res);}- if (unlikely(res))- memset(to + (n - res), 0, res);+ instrument_copy_from_user_before(to, from, n);+ res = raw_copy_from_user(to, from, n);+ instrument_copy_from_user_after(to, from, n, res);+ if (likely(!res))+ return 0;+fail:+ memset(to + (n - res), 0, res);return res;}extern __must_check unsigned long
该补丁已合并到 Linux 内核的 Git 代码仓库中，并将成为 11 月下旬发布的 Linux 6.12 稳定版的一部分。
详情查看发布公告：
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=0fc810ae3ae110f9e2fcccce80fc8c8d62f97907
---END---
