linux-kernel - Re: [patch V4 10/15] x86/entry: Use generic syscall entry function

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Message-ID: <87wo2vz9sc.fsf@nanos.tec.linutronix.de>
Date:   Wed, 22 Jul 2020 20:25:55 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Kees Cook <keescook@...omium.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        linux-arch@...r.kernel.org, Will Deacon <will@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Mark Rutland <mark.rutland@....com>,
        Keno Fischer <keno@...iacomputing.com>,
        Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        Gabriel Krisman Bertazi <krisman@...labora.com>
Subject: Re: [patch V4 10/15] x86/entry: Use generic syscall entry function

Kees,

Kees Cook <keescook@...omium.org> writes:
> On Tue, Jul 21, 2020 at 12:57:16PM +0200, Thomas Gleixner wrote:
>
> This doesn't look very expensive, and they certain indicate really bad
> conditions. Does this need to be behind a CONFIG? (Whatever the answer,
> we can probably make those changes in a later series -- some of these
> also look not arch-specific...)

The most expensive part is native_save_flags(). The extra branches could
be visible in benchmarks, but its a good question whether this should be
just enabled.

I just keep it as is for now as I would need to make the flags and the
on_thread_stack() part x86 specific anyway, but yes we can revisit that
once we agreed on the general direction of this.

Thanks,

        tglx