That's not true. You can get those faults even without a PMP if you try and access non-existent memory or if the hardware gives a bus fault due to an access that's not legal for a given peripheral.

Those would also be unrecoverable errors, right?

The problem I'm trying to address here is that if FreeBSD touches PMP protected memory it'll get a load/store/fetch fault and right now it treats that like a TLB miss, tries to load the right page table entry and then tries again. Which faults again, which ...

(And as an aside, is there a better resource about RISC-V in these situations than "RISC-V Instruction Set Manual: Volume II: Privileged Architecture"? I can't seem to find anything relevant about bus errors there, but I may also be overlooking it.)

Panicking here makes sense. Perhaps call it a "memory access exception" rather than a "PMP violation" per Jess's comment. I don't know of any other reference besides the priv spec.

Yeah, the privileged spec calls each an "X access fault". The non-PMP discussion is in the "Physical Memory Attributes" section, and is a more general thing that can include bus faults on implementations where they can occur.

Should we be doing something for user load/store/fetch faults? Probably a SIGBUS?

Or maybe a panic if we don't expect that to ever happen (though if you start doing memory-mapped devices that's no longer the case).

In D26544#592591, @jrtc27 wrote:

Should we be doing something for user load/store/fetch faults? Probably a SIGBUS?

Yes, we should.

See https://reviews.freebsd.org/D26621

I mmap()ed /dev/mem and accessed PMP protected memory. I see the same endless fault loop as in kernel mode, but it's easily "fixed" by terminating the process.

I did need to implement /dev/mem mmap to test that: https://reviews.freebsd.org/D26622