linux-kernel - Re: [GIT PULL] x86 cleanups for v5.7

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Message-ID: <CAHk-=whkQwEJxg9XBO9nBk=aCade8Obk+EvVjzTRT1R+nq3eYw@mail.gmail.com>
Date:   Thu, 2 Apr 2020 11:13:28 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Andy Lutomirski <luto@...capital.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michael Matz <matz@...e.de>
Subject: Re: [GIT PULL] x86 cleanups for v5.7

On Thu, Apr 2, 2020 at 11:04 AM Borislav Petkov <bp@...en8.de> wrote:
>
> My only worry is that if we had that support, we would have to keep two
> versions of the facilities which use it - one with asm goto with outputs
> and one without.

That's why it took three years for me to merge the "unsafe_put_user()"
stuff. I only did it once other issues had made PeterZ and people
decide that "asm goto is a required feature" for some of the other
stuff (static branches, whatever).

Because when it comes to small details like "we can remove a test and
a branch", it generally isn't worth the code complexity to have two
different copies. Particularly with how messy uaccess.h was.

The reason I did the additional uaccess.h cleanups was exactly because
I think I can have a CONFIG_ASM_GOTO_OUTPUTS thing, and minimize the
differences the same way we minimize them with CC_SET/CC_OUT doe the
__GCC_ASM_FLAG_OUTPUTS__ compiler support flag.

I haven't actually sat down to _do_ it, though. I spent several hours
on the cleanups as a break from pulling stuff during the merge window,
but this _is_ my busy time..

              Linus