reserved-memory nodes created by OpenSBI

[Anup Patel]

On Tue, May 23, 2023 at 7:13 PM Oleksii Kurochko
<oleksii.kurochko at gmail.com> wrote:
>
> Hello, dear community,
>
> I would like to ask you about reserved-memory nodes, which are created
> by OpenSBI here:
> https://github.com/riscv-software-src/opensbi/blob/v1.2/lib/utils/fdt/fdt_fixup.c#LL198C5-L198C30)/
>
> The questions are the following:
> 1. What is the purpose of extending dts by reserved-memory nodes? I
> assume that it is necessary to reserve some memory ranges for OpenSBI.
> 2. Why OpenSBI needs to have a preserved memory?
> 3. The memory-reserved ranges are overlapped with Linux's memory node
> range. Is it OK that OpenSBI's memory-reserved node ranges and Linux's
> memory node ranges overlap?

OpenSBI uses reserved-memory DT nodes to inform the next booting
stage (including Linux) about the memory used by OpenSBI firmware.

If these reserved-memory DT nodes are not present then supervisor
OS (Linux) might crash accessing the memory used by OpenSBI
because OpenSBI protects its own memory using PMP.

Regards,
Anup

>
> Thanks.
>
> ~ Oleksii
>
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