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 <kbusch@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 8f0e0749a5812830e36864edb886b19eb53e770f..4cd0ee52710dd184f8a2d78cab51697c009c8427 100644 (file)
--- a/io_uring/io_uring.c
+++ b/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,