Redundant barrier_nospec() added by commit 74e19ef0ff80 ("uaccess: Add speculation barrier to copy_from_user()")

[Christophe Leroy]

Hello Dave,

In commit 74e19ef0ff80 ("uaccess: Add speculation barrier to 
copy_from_user()") you add barrier_nospec() to copy_from_user().

There is already a barrier_nospec() in allow_read_from_user() which is 
called by raw_copy_from_user(), see commit 8524e2e76441 
("powerpc/uaccess: Perform barrier_nospec() in KUAP allowance helpers"). 
Why do you need an additional one ?

And why only copy_from_user() and not also other places like 
copy_from_user_iter() for instance ?

Thanks
Christophe