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From:   Andy Lutomirski <luto@kernel.org>
Date:   Thu, 25 Jan 2018 13:08:38 -0800
Message-ID: <CALCETrV1JHK1ovjjD1vbs08K1an6tq6nbRoAj9uyrY2GUYJJBA@mail.gmail.com>
Subject: Re: [PATCH] x86/retpoline/entry: Disable the entire SYSCALL64 fast
 path with retpolines on
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Andy Lutomirski <luto@kernel.org>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Alan Cox <alan@linux.intel.com>, Jann Horn <jannh@google.com>,
        Samuel Neves <samuel.c.p.neves@gmail.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Kernel Hardening <kernel-hardening@lists.openwall.com>,
        Borislav Petkov <bp@alien8.de>
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On Thu, Jan 25, 2018 at 1:06 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Thu, Jan 25, 2018 at 1:02 PM, Andy Lutomirski <luto@kernel.org> wrote:
>>
>> Feel free to Acked-by: Andy Lutomirski <luto@kernel.org> that patch.
>>
>> Or I can grab it and send it to -tip.
>
> I'm not going to apply it for 4.15, I just wanted to see how it
> looked, and do some minimal profiling.
>
> From the profiles, as mentioned, moving 'status' from thread_struct to
> thread_info is probably worth doing. But I didn't look at the impact
> of that at all.
>
> So it should go through all the normal channels in -tip for 4.16.
>
> I'll happily sign off on the patch, but it was really pretty mindless,
> so I'm not sure I need the authorship either.
>
>> Re: the trampoline not showing up: if I find some time, I'll try to
>> wire it up correctly in kallsyms.
>
> That would be lovely. Right now the system call exit shows up pretty
> clearly in profiles, and most of it is (obviously) the cr3 write. So
> the missing entry trampoline is not insignificant.
>

With retpoline, the retpoline in the trampoline sucks.  I don't need
perf for that -- I've benchmarked it both ways.  It sucks.  I'll fix
it, but it'll be kind of complicated.

--Andy