[PATCH v2 20/20] platform: generic: mips eyeq7h: prohibit accessing memory beyond DRAM

[Vladimir Kondratiev]

On 2/22/26 18:03, Anup Patel wrote:
>> SBI code arranges domain PMP regions in a way that last entry is
>> all-inclusive "0..~0 RWX" and the rest of entries are not programmed.
>> This causes 2 problems for the eyeq7h.
>>
>> 1) Remaining entries from the boot loader.
>> When PMP is actually programmed on the later stage, only defined entries
>> get programmed. Therefore, if boot code configured some entries beyond
>> what is set in domain configuration, it will be untouched. Ex: boot code
>> sets entries 14 and 15, leaving others unconfigured. To prevent such
>> left over PMP entries, domain should configure all possible PMP regions.
> Better disable unused PMP entries in generic code itself. Basically,
> sbi_hart_oldpmp_configure() and sbi_hart_smepmp_configure()
> can disable unused PMP entries at the end just before calling
> sbi_hart_pmp_fence().

Agree, this is possible. Question is whether all platforms are OK
with this, meaning no one relies on boot loader configured PMPs.

I will prepare patch that disable non-configured PMP entries instead of not
touching it as it is today.

Thanks, Vladimir.
> 
>> 2) speculative prefetches
>> CPU can issue speculative prefetches to non-existent addresses. If this
>> access goes to the system NOC, it is mis-interpreted as an access
>> violation and error is reported, forcing system reset.
>>
>> To prevent such a speculative transaction to leave a CPU cluster,
>> block it using PMP, by restricting memory region to physically present
>> memory.
> The unused PMP entries are typically used when we have
> multiple domains on a platform (e.g. non-secure domain and
> secure domain). Consuming unused PMP entries to block
> speculative transactions leaves no PMP entries for system-level
> partitioning using domains.
> 
> I assume MIPS does not want to support OpenSBI domain
> on their platforms ??

So far I see only root domain. If multiple domains will be supported by
OpenSBI, no reason why not support it on the p8700 platform.

Thanks, Vladimir