RE: [PATCH v2 0/2] Replace and improve "mcsafe" with copy_safe()

[Luck, Tony]

> Now maybe copy_to_user() should *always* work this way, but Iâm not convinced.
> Certainly put_user() shouldnât â the result wouldnât even be well defined. And Iâm
>  unconvinced that it makes much sense for the majority of copy_to_user() callers
>  that are also directly accessing the source structure.

One case that might work is copy_to_user() that's copying from the kernel page cache
to the user in response to a read(2) system call.  Action would be to check if we could
re-read from the file system to a different page. If not, return -EIO. Either way ditch the
poison page from the page cache.

-Tony