linux-kernel - Re: [RFC v1 0/4] arm64: MMU enabled kexec kernel relocation

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Date:   Wed, 17 Jul 2019 00:44:45 +0530
From:   Bhupesh Sharma <bhsharma@...hat.com>
To:     Pavel Tatashin <pasha.tatashin@...een.com>
Cc:     James Morris <jmorris@...ei.org>, sashal@...nel.org,
        Eric Biederman <ebiederm@...ssion.com>,
        kexec mailing list <kexec@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>,
        Catalin Marinas <catalin.marinas@....com>, will@...nel.org,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC v1 0/4] arm64: MMU enabled kexec kernel relocation

Hi Pavel,

On Tue, Jul 16, 2019 at 10:26 PM Pavel Tatashin
<pasha.tatashin@...een.com> wrote:
>
> Added identity mapped page table, and keep MMU enabled while
> kernel is being relocated from sparse pages to the final
> destination during kexec.
>
> More description about the problem I am trying to solve here, can be
> found here:
> https://lore.kernel.org/lkml/20190709182014.16052-1-pasha.tatashin@soleen.com/
>
> This patch series works in terms, that I can kexec-reboot both in QEMU
> and on a physical machine. However, I do not see performance improvement
> during relocation. The performance is just as slow as before with disabled
> caches.

Thanks for the patchset, but if the changes still don't positively
impact the kexec-reboot timings, I am not sure we if gain by adding
these to the kernel.

Like I mentioned in the previous threads, we have been carrying some
relevant fixes for the same in Linux distros. I have been trying to
find time to fix them and send them upstream, but I am caught up with
some nasty kexec_file_load() issues on arm64 currently.

So, I will find some time to work on them (may be next week) and will
Cc you when I post them out after some checks on real physical
hardware.

Thanks,
Bhupesh

> Am I missing something? Perhaps, there is some flag that I should also
> enable in page table? Please provide me with any suggestions.
>
> Pavel Tatashin (4):
>   arm64, mm: identity mapped page table
>   arm64, kexec: interface preparation for mmu enabled kexec
>   arm64, kexec: add kexec's own identity page table
>   arm64: Keep MMU on while kernel is being relocated
>
>  arch/arm64/include/asm/ident_map.h  |  26 ++++++
>  arch/arm64/include/asm/kexec.h      |   5 +-
>  arch/arm64/kernel/cpu-reset.S       |   8 --
>  arch/arm64/kernel/cpu-reset.h       |   7 +-
>  arch/arm64/kernel/machine_kexec.c   | 128 +++++++++++++++++++++-------
>  arch/arm64/kernel/relocate_kernel.S |  36 +++++---
>  arch/arm64/mm/Makefile              |   1 +
>  arch/arm64/mm/ident_map.c           |  99 +++++++++++++++++++++
>  8 files changed, 255 insertions(+), 55 deletions(-)
>  create mode 100644 arch/arm64/include/asm/ident_map.h
>  create mode 100644 arch/arm64/mm/ident_map.c
>
> --
> 2.22.0
>
>
> _______________________________________________
> kexec mailing list
> kexec@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/kexec

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