linux-kernel - Re: [PATCH v3 10/13] x86/retpoline/pvops: Convert assembler indirect jumps

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Message-ID: <20180104163702.GM25156@tassilo.jf.intel.com>
Date:   Thu, 4 Jan 2018 08:37:02 -0800
From:   Andi Kleen <ak@...ux.intel.com>
To:     Juergen Gross <jgross@...e.com>
Cc:     David Woodhouse <dwmw@...zon.co.uk>, Paul Turner <pjt@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>, tglx@...utronix.de,
        Kees Cook <keescook@...gle.com>,
        Rik van Riel <riel@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...capital.net>,
        Jiri Kosina <jikos@...nel.org>, gnomes@...rguk.ukuu.org.uk
Subject: Re: [PATCH v3 10/13] x86/retpoline/pvops: Convert assembler indirect
 jumps

On Thu, Jan 04, 2018 at 04:02:06PM +0100, Juergen Gross wrote:
> On 04/01/18 15:37, David Woodhouse wrote:
> > Convert pvops invocations to use non-speculative call sequences, when
> > CONFIG_RETPOLINE is enabled.
> > 
> > There is scope for future optimisation here — once the pvops methods are
> > actually set, we could just turn the damn things into *direct* jumps.
> > But this is perfectly sufficient for now, without that added complexity.
> 
> I don't see the need to modify the pvops calls.
> 
> All indirect calls are replaced by either direct calls or other code
> long before any user code is active.
> 
> For modules the replacements are in place before the module is being
> used.

Agreed. This shouldn't be needed.

-Andi