linux-kernel - Re: [v1 0/5] allow to reserve memory for normal kexec kernel

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Date:   Thu, 11 Jul 2019 08:26:16 -0400
From:   Pavel Tatashin <pasha.tatashin@...een.com>
To:     Vladimir Murzin <vladimir.murzin@....com>
Cc:     James Morse <james.morse@....com>, Sasha Levin <sashal@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Catalin Marinas <catalin.marinas@....com>,
        Bhupesh Sharma <bhsharma@...hat.com>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        kexec mailing list <kexec@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        James Morris <jmorris@...ei.org>,
        Eric Biederman <ebiederm@...ssion.com>, will@...nel.org,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [v1 0/5] allow to reserve memory for normal kexec kernel

On Thu, Jul 11, 2019 at 4:12 AM Vladimir Murzin <vladimir.murzin@....com> wrote:
>
> Hi,
>
> On 7/10/19 4:56 PM, Pavel Tatashin wrote:
> > On Wed, Jul 10, 2019 at 11:19 AM James Morse <james.morse@....com> wrote:
> >>
> >> Hi Pasha,
> >>
> >> On 09/07/2019 14:07, Pavel Tatashin wrote:
> >>>>> Enabling MMU and D-Cache for relocation  would essentially require the
> >>>>> same changes in kernel. Could you please share exactly why these were
> >>>>> not accepted upstream into kexec-tools?
> >>>>
> >>>> Because '--no-checks' is a much simpler alternative.
> >>>>
> >>>> More of the discussion:
> >>>> https://lore.kernel.org/linux-arm-kernel/5599813d-f83c-d154-287a-c131c48292ca@arm.com/
> >>>>
> >>>> While you can make purgatory a fully-fledged operating system, it doesn't really need to
> >>>> do anything on arm64. Errata-workarounds alone are a reason not do start down this path.
> >>>
> >>> Thank you James. I will summaries the information gathered from the
> >>> yesterday's/today's discussion and add it to the cover letter together
> >>> with ARM64 tag. I think, the patch series makes sense for ARM64 only,
> >>> unless there are other platforms that disable caching/MMU during
> >>> relocation.
> >>
> >> I'd prefer not to reserve additional memory for regular kexec just to avoid the relocation.
> >> If the kernel's relocation work is so painful we can investigate doing it while the MMU is
> >> enabled. If you can compare regular-kexec with kexec_file_load() you eliminate the
> >> purgatory part of the work.
> >
> > Relocation time is exactly the same for regular-kexec and
> > kexec_file_load(). So, the relocation is indeed painful for our case.
> > I am working on adding MMU enabled kernel relocation.
>
> Out of curiosity, does enabling only I-cache make a difference? IIRC, it doesn't
> require setting MMU, in contrast to D-cache.

Resend:

Thank you for suggestion. I have actually experimented with enabling
caches without MMU. Did not see a difference.

Thank you,
Pasha

>
> Cheers
> Vladimir
>
> >
> > Pasha
> >
> > _______________________________________________
> > linux-arm-kernel mailing list
> > linux-arm-kernel@...ts.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
> >
>

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