io_uring: change io_get_ext_arg() to use uaccess begin + end

In scenarios where a high frequency of wait events are seen, the copy
of the struct io_uring_getevents_arg is quite noticeable in the
profiles in terms of time spent. It can be seen as up to 3.5-4.5%.
Rewrite the copy-in logic, saving about 0.5% of the time.

Reviewed-by: Keith Busch <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>

Author: axboe

io_uring/io_uring.c

@@ -3240,6 +3240,7 @@ static int io_validate_ext_arg(unsigned flags, const void __user *argp, size_t a
 static int io_get_ext_arg(unsigned flags, const void __user *argp,
 			  struct ext_arg *ext_arg)
 {
+	const struct io_uring_getevents_arg __user *uarg = argp;
 	struct io_uring_getevents_arg arg;
 
 	/*
@@ -3257,8 +3258,18 @@ static int io_get_ext_arg(unsigned flags, const void __user *argp,
 	 */
 	if (ext_arg->argsz != sizeof(arg))
 		return -EINVAL;
-	if (copy_from_user(&arg, argp, sizeof(arg)))
+#ifdef CONFIG_64BIT
+	if (!user_access_begin(uarg, sizeof(*uarg)))
 		return -EFAULT;
+	unsafe_get_user(arg.sigmask, &uarg->sigmask, uaccess_end);
+	unsafe_get_user(arg.sigmask_sz, &uarg->sigmask_sz, uaccess_end);
+	unsafe_get_user(arg.min_wait_usec, &uarg->min_wait_usec, uaccess_end);
+	unsafe_get_user(arg.ts, &uarg->ts, uaccess_end);
+	user_access_end();
+#else
+	if (copy_from_user(&arg, uarg, sizeof(arg)))
+		return -EFAULT;
+#endif
 	ext_arg->min_time = arg.min_wait_usec * NSEC_PER_USEC;
 	ext_arg->sig = u64_to_user_ptr(arg.sigmask);
 	ext_arg->argsz = arg.sigmask_sz;
@@ -3268,6 +3279,11 @@ static int io_get_ext_arg(unsigned flags, const void __user *argp,
 		ext_arg->ts_set = true;
 	}
 	return 0;
+#ifdef CONFIG_64BIT
+uaccess_end:
+	user_access_end();
+	return -EFAULT;
+#endif
 }
 
 SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,