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

[Will Deacon]

[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