linux-kernel - Re: [PATCH v9 08/18] arm64: kexec: move relocation function setup

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Date:   Fri, 22 Jan 2021 20:01:21 -0500
From:   Pavel Tatashin <pasha.tatashin@...een.com>
To:     James Morse <james.morse@....com>
Cc:     James Morris <jmorris@...ei.org>, Sasha Levin <sashal@...nel.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        kexec mailing list <kexec@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Marc Zyngier <maz@...nel.org>,
        Vladimir Murzin <vladimir.murzin@....com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        linux-mm <linux-mm@...ck.org>,
        Mark Rutland <mark.rutland@....com>, steve.capper@....com,
        rfontana@...hat.com, Thomas Gleixner <tglx@...utronix.de>,
        Selin Dag <selindag@...il.com>
Subject: Re: [PATCH v9 08/18] arm64: kexec: move relocation function setup

On Wed, Apr 29, 2020 at 1:01 PM James Morse <james.morse@....com> wrote:
>
> Hi Pavel,
>
> On 26/03/2020 03:24, Pavel Tatashin wrote:
> > Currently, kernel relocation function is configured in machine_kexec()
> > at the time of kexec reboot by using control_code_page.
> >
> > This operation, however, is more logical to be done during kexec_load,
> > and thus remove from reboot time. Move, setup of this function to
> > newly added machine_kexec_post_load().
>
> This would avoid the need to special-case the cache maintenance, so its a good cleanup...

Yes, the computation should be moved from kexec-reboot to kexec-load
when possible.

>
>
> > Because once MMU is enabled, kexec control page will contain more than
> > relocation kernel, but also vector table, add pointer to the actual
> > function within this page arch.kern_reloc. Currently, it equals to the
> > beginning of page, we will add offsets later, when vector table is
> > added.
>
> If the vector table always comes second, wouldn't this be extra work to hold the value 0?
> You can control the layout of this relocation code, as it has to be written in assembly.
> I don't get why this would be necessary.
>
>
> > diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c
> > index ae1bad0156cd..ec71a153cc2d 100644
> > --- a/arch/arm64/kernel/machine_kexec.c
> > +++ b/arch/arm64/kernel/machine_kexec.c
> > @@ -58,6 +59,17 @@ void machine_kexec_cleanup(struct kimage *kimage)
> >       /* Empty routine needed to avoid build errors. */
> >  }
> >
> > +int machine_kexec_post_load(struct kimage *kimage)
> > +{
> > +     void *reloc_code = page_to_virt(kimage->control_code_page);
> > +
> > +     memcpy(reloc_code, arm64_relocate_new_kernel,
> > +            arm64_relocate_new_kernel_size);
> > +     kimage->arch.kern_reloc = __pa(reloc_code);
>
> Could we move the two cache maintenance calls for this area in here too. Keeping it next
> to the modification makes it clearer why it is required.

Yes, I moved it.

>
> In this case we can use flush_icache_range() instead of its __variant because this now
> happens much earlier.

True.

>
>
> > +     return 0;
> > +}
>
> Regardless,
> Reviewed-by: James Morse <james.morse@....com>

Thank you for your review.

Pasha

>
>
> Thanks,
>
> James