linux-kernel - Re: [PATCH] Convert filldir[64]() from __put_user() to unsafe_put

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Message-ID: <CAHk-=wgO1EW5qVuy7=sc9Kua98-afMx75gaeX4FHKf3+wPLmkw@mail.gmail.com>
Date:   Sun, 13 Oct 2019 13:20:33 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH] Convert filldir[64]() from __put_user() to unsafe_put_user()

On Sun, Oct 13, 2019 at 12:59 PM Al Viro <viro@...iv.linux.org.uk> wrote:
>
> Re plotting: how strongly would you object against passing the range to
> user_access_end()?  Powerpc folks have a very close analogue of stac/clac,
> currently buried inside their __get_user()/__put_user()/etc. - the same
> places where x86 does, including futex.h and friends.
>
> And there it's even costlier than on x86.  It would obviously be nice
> to lift it at least out of unsafe_get_user()/unsafe_put_user() and
> move into user_access_begin()/user_access_end(); unfortunately, in
> one subarchitecture they really want it the range on the user_access_end()
> side as well.

Hmm. I'm ok with that.

Do they want the actual range, or would it prefer some kind of opaque
cookie that user_access_begin() returns (where 0 would mean "failure"
of course)?

I'm thinking like a local_irq_save/restore thing, which might be the
case on yet other architectures.

         Linus