[PATCH 2/3] io_uring: change io_get_ext_arg() to use uaccess begin + end

[Jens Axboe <axboe@kernel.dk>]

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 <kbusch@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 io_uring/io_uring.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 8952453ea807..bfea5d1fbc67 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -3239,6 +3239,7 @@ 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;
 
 	/*
@@ -3256,8 +3257,19 @@ 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)))
+	if (!user_access_begin(uarg, sizeof(*uarg)))
 		return -EFAULT;
+#ifdef CONFIG_64BIT
+	unsafe_get_user(arg.sigmask, &uarg->sigmask, uaccess_end);
+	unsafe_get_user(arg.ts, &uarg->ts, uaccess_end);
+#else
+	unsafe_copy_from_user(&arg.sigmask, &uarg->sigmask, sizeof(arg.sigmask),
+				uaccess_end);
+	unsafe_copy_from_user(&arg.ts, &uarg->ts, sizeof(arg.ts), uaccess_end);
+#endif
+	unsafe_get_user(arg.min_wait_usec, &uarg->min_wait_usec, uaccess_end);
+	unsafe_get_user(arg.sigmask_sz, &uarg->sigmask_sz, uaccess_end);
+	user_access_end();
 	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;
@@ -3267,6 +3279,9 @@ static int io_get_ext_arg(unsigned flags, const void __user *argp,
 		ext_arg->ts_set = true;
 	}
 	return 0;
+uaccess_end:
+	user_access_end();
+	return -EFAULT;
 }
 
 SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
-- 
2.45.2