iov_iter: Mark copy_compat_iovec_from_user() noinline

JIRA: https://issues.redhat.com/browse/RHEL-87739

commit 50f9a76
Author: Josh Poimboeuf <jpoimboe@kernel.org>
Date:   Wed Apr 12 10:46:48 2023 -0600

    iov_iter: Mark copy_compat_iovec_from_user() noinline

    After commit 6376ce56feb6 ("iov_iter: import single vector iovecs as
    ITER_UBUF"), GCC does an inter-procedural compiler optimization which
    moves the user_access_begin() out of copy_compat_iovec_from_user() and
    into its callers:

      lib/iov_iter.o: warning: objtool: .altinstr_replacement+0x0: redundant UACCESS disable
      lib/iov_iter.o: warning: objtool: iovec_from_user.part.0+0xc7: call to copy_compat_iovec_from_user.part.0() with UACCESS enabled
      lib/iov_iter.o: warning: objtool: __import_iovec+0x21d: call to copy_compat_iovec_from_user.part.0() with UACCESS enabled

    Enforce the "no UACCESS enable across function boundaries" rule by
    disabling cloning for copy_compat_iovec_from_user().

    Fixes: 6376ce56feb6 ("iov_iter: import single vector iovecs as ITER_UBUF")
    Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
    https://lkml.kernel.org/lkml/20230327120017.6bb826d7@canb.auug.org.au
    Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
    Tested-by: Jens Axboe <axboe@kernel.dk>
    Signed-off-by: Jens Axboe <axboe@kernel.dk>

Signed-off-by: Ming Lei <ming.lei@redhat.com>

Author: Ming Lei

lib/iov_iter.c

@@ -1747,7 +1747,7 @@ const void *dup_iter(struct iov_iter *new, struct iov_iter *old, gfp_t flags)
 }
 EXPORT_SYMBOL(dup_iter);
 
-static int copy_compat_iovec_from_user(struct iovec *iov,
+static __noclone int copy_compat_iovec_from_user(struct iovec *iov,
 		const struct iovec __user *uvec, unsigned long nr_segs)
 {
 	const struct compat_iovec __user *uiov =