[PATCH 0/7] lib: sbi: Probe PMP locked entries and adjust first usable PMP index

[Anup Patel]

On Fri, Dec 8, 2023 at 3:32 AM Yangyu Chen <cyy at cyyself.name> wrote:
>
> Some platform which has different domains for different CPU cores may
> disable some device by PMP in the bootloader. For example, Canaan
> Kendryte K230 provides SDK which locks some PMP entries in M-Mode
> U-Boot[1]. As a result, the mainline OpenSBI running on this bootloader
> will probe the PMP Count = 1 instead of 64 and PMP Granularity = 4
> instead of 4096, which will cause the OpenSBI to have not enough PMPs to
> set such regions and the only probed PMP entry is locked. Thus, we will
> have no PMP to allow S-Mode main memory access, causing the S-Mode
> software traps due to Instruction Access Fault over and over again and
> never executed.
>
> This patch set probes the PMP locked entries and adjusts the first
> usable PMP index to the maximum index of PMP locked entries + 1. Thus,
> the OpenSBI will skip the PMP entries which are locked before OpenSBI
> starts.

I thought about this for quite some time. This idea of previous booting
staging locking PMP entries is not going to fly.

If you want platform specific reserved PMP entries then you can always
add a generic platform override which adds these PMP entries.

Please reconsider and fix your boot flow.

Regards,
Anup

>
> [1] https://github.com/kendryte/k230_sdk/blob/72be167ad4b3a7e91f7cc6abbe576d347b885af4/src/little/uboot/arch/riscv/cpu/k230/cpu.c#L82
>
> Yangyu Chen (7):
>   lib: sbi: Probe pmp_count in read-only
>   lib: sbi: detect the number of PMP entries first
>   lib: sbi: Probe reserved PMP regions before OpenSBI start
>   lib: sbi: probe PMP allowed addr from first usable PMP
>   lib: sbi: adjust first usable PMP index to sbi_hart_pmp_reserved
>   lib: sbi: Not use smepmp if has pmp reserved and MSECCFG.MML=1
>   lib: sbi: show the number of PMP Reserved
>
>  include/sbi/sbi_hart.h |  4 +-
>  lib/sbi/sbi_hart.c     | 87 +++++++++++++++++++++++++++++++-----------
>  lib/sbi/sbi_init.c     |  2 +
>  3 files changed, 69 insertions(+), 24 deletions(-)
>
> --
> 2.43.0
>
>
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