Re: [PATCH 0/2] arm64: kexec_file_load vs memory reservations

[Fixing Bhupesh's email address]

On Thu, Apr 29, 2021 at 02:35:31PM +0100, Marc Zyngier wrote:

It recently became apparent that using kexec with kexec_file_load() on
arm64 is pretty similar to playing Russian roulette.

Depending on the amount of memory, the HW supported and the firmware
interface used, your secondary kernel may overwrite critical memory
regions without which the secondary kernel cannot boot (the GICv3 LPI
tables being a prime example of such reserved regions).

It turns out that there is at least two ways for reserved memory
regions to be described to kexec: /proc/iomem for the userspace
implementation, and memblock.reserved for kexec_file. And of course,
our LPI tables are only reserved using the resource tree, leading to
the aforementioned stamping. Similar things could happen with ACPI
tables as well.

On my 24xA53 system artificially limited to 256MB of RAM (yes, it
boots with that little memory), trying to kexec a secondary kernel
failed every times. I can only presume that this was mostly tested
using kdump, which preserves the entire kernel memory range.

This small series aims at triggering a discussion on what are the
expectations for kexec_file, and whether we should unify the two
reservation mechanisms.

Bhupesh, since you've been involved with kexec file on arm64 before, please
could you take a look at these patches?

Thanks,

Will

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