linux-kernel - Re: [PATCH 3/3] jump_label: make initial NOP patching the special case

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Date:   Wed, 15 Jun 2022 12:20:23 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Mark Rutland <mark.rutland@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        "open list:MIPS" <linux-mips@...r.kernel.org>,
        "open list:S390" <linux-s390@...r.kernel.org>
Subject: Re: [PATCH 3/3] jump_label: make initial NOP patching the special case

On Wed, 15 Jun 2022 at 12:06, Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Wed, Jun 15, 2022 at 10:52:41AM +0100, Mark Rutland wrote:
> > On Wed, Jun 08, 2022 at 12:45:12PM +0200, Ard Biesheuvel wrote:
> > > Instead of defaulting to patching NOP opcodes at init time, and leaving
> > > it to the architectures to override this if this is not needed, switch
> > > to a model where doing nothing is the default. This is the common case
> > > by far, as only MIPS requires NOP patching at init time. On all other
> > > architectures, the correct encodings are emitted by the compiler and so
> > > no initial patching is needed.
> > >
> > > Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
> > > ---
> > >  Documentation/staging/static-keys.rst |  3 ---
> > >  arch/arc/kernel/jump_label.c          | 13 -------------
> > >  arch/arm/kernel/jump_label.c          |  6 ------
> > >  arch/arm64/kernel/jump_label.c        | 11 -----------
> > >  arch/mips/include/asm/jump_label.h    |  2 ++
> > >  arch/parisc/kernel/jump_label.c       | 11 -----------
> > >  arch/riscv/kernel/jump_label.c        | 12 ------------
> > >  arch/s390/kernel/jump_label.c         |  5 -----
> > >  arch/x86/kernel/jump_label.c          | 13 -------------
> > >  kernel/jump_label.c                   | 14 +++-----------
> > >  10 files changed, 5 insertions(+), 85 deletions(-)
> >
> > I have one minor comment below, but either way this is a nice cleanup (and I'm
> > always happy to see __weak functions disappear), so FWIW:
>
> (I've got a new found hatred for __weak after having had to fix so many
> objtool issues with it, so yeah, that).
>
> >
> >   Acked-by: Mark Rutland <mark.rutland@....com>
>
> With the thing Mark pointed out fixed:
>
> Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
>
> (although, I'll probably be the one to eventually apply these I suppose,
> unless they're needed in a different tree?)

Not really - this just came up when Jason was looking into how to
enable jump labels extremely early on every single architecture, but
fortunately, that issue got fixed in a different way.

I'll respin and resend and leave it to you to apply them whenever convenient.