linux-kernel - Re: [PATCH v2 0/2] efi: arm64: Introduce /proc/efi/memreserve to tell the persistent pages

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Date:   Wed, 4 Dec 2019 09:51:13 +0000
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Masayoshi Mizuma <msys.mizuma@...il.com>,
        James Morse <james.morse@....com>
Cc:     linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-efi <linux-efi@...r.kernel.org>,
        Masayoshi Mizuma <m.mizuma@...fujitsu.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Kexec Mailing List <kexec@...ts.infradead.org>,
        d.hatayama@...itsu.com, Eric Biederman <ebiederm@...ssion.com>,
        Matthias Brugger <matthias.bgg@...il.com>
Subject: Re: [PATCH v2 0/2] efi: arm64: Introduce /proc/efi/memreserve to tell
 the persistent pages

On Tue, 3 Dec 2019 at 20:14, Masayoshi Mizuma <msys.mizuma@...il.com> wrote:
>
> From: Masayoshi Mizuma <m.mizuma@...fujitsu.com>
>
> kexec reboot sometime fails in early boot sequence on aarch64 machine.
> That is because kexec overwrites the LPI property tables and pending
> tables with the initrd.
>
> To avoid the overwrite, introduce /proc/efi/memreserve to tell the
> tables region to kexec so that kexec can avoid the memory region to
> locate initrd.
>
> kexec also needs a patch to handle /proc/efi/memreserve. I'm preparing
> the patch for kexec.
>
> Changelog
>     v2: - Change memreserve file location from sysfs to procfs.
>           memreserve may exceed the PAGE_SIZE in case efi_memreserve_root
>           has a lot of entries. So we cannot use sysfs_kf_seq_show().
>           Use seq_printf() in procfs instead.
>
> Masayoshi Mizuma (2):
>   efi: add /proc/efi directory
>   efi: arm64: Introduce /proc/efi/memreserve to tell the persistent
>     pages
>

Apologies for the tardy response.

Adding /proc/efi is really out of the question. *If* we add any
special files to expose this information, it should be under sysfs.

However, this is still only a partial solution, since it only solves
the problem for userspace based kexec, and we need something for
kexec_file_load() as well.

The fundamental issue here is that /proc/iomem apparently lacks the
entries that describe these regions as 'reserved', so we should try to
address that instead.