linux-kernel - Re: [PATCH 5/5] x86/kernel: jump

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Message-ID: <20180628092815.GD2494@hirez.programming.kicks-ass.net>
Date:   Thu, 28 Jun 2018 11:28:15 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Arnd Bergmann <arnd@...db.de>,
        Steven Rostedt <rostedt@...dmis.org>, namit@...are.com
Subject: Re: [PATCH 5/5] x86/kernel: jump_table: use relative references

On Thu, Jun 28, 2018 at 10:34:54AM +0200, Ard Biesheuvel wrote:
> On 28 June 2018 at 10:31, Peter Zijlstra <peterz@...radead.org> wrote:
> > On Wed, Jun 27, 2018 at 06:06:04PM +0200, Ard Biesheuvel wrote:
> >> Similar to the arm64 case, 64-bit x86 can benefit from using 32-bit
> >> relative references rather than 64-bit absolute ones when emitting
> >> struct jump_entry instances. Not only does this reduce the memory
> >> footprint of the entries themselves by 50%, it also removes the need
> >> for carrying relocation metadata on relocatable builds (i.e., for KASLR)
> >> which saves a fair chunk of .init space as well (although the savings
> >> are not as dramatic as on arm64)
> >
> > This will conflict with:
> >
> >   https://lkml.kernel.org/r/20180622172212.199633-10-namit@vmware.com
> 
> Thanks for the head's up. Fortunately, it does not conflict
> fundamentally, so it should be a straight-forward rebase after that
> code is merged.

Yeah, shouldn't be hard to cure.

There's another patch set that might have a little conflict, but that's
not near ready I think, so that'll have to just cope with things
shifting underneath (and there too, the fixup shouldn't be hard).

> Do you think this is likely to get merged for v4.19?

I'm thinking it is near ready so it might, but I'm not in charge of
those bits :-)