riscv vmm: various fixes in APLIC

[br]

Summary

• Implement level-sensitive interrupts
• Disable up to 32 interrupts by a single query (CLRIE register handling)
• Implement reading from DOMAINCFG

This is a minimal set of changes needed to boot Linux guest.

More work TODO to handle other APLIC registers read/write.

Test Plan

Linux booting in 0.48s with this. FreeBSD also speeds up for some reason

[markj]

sys/riscv/vmm/vmm_aplic.c

178

180

Do you want to check the return value here?

304

Why isn't the mutex required here?

[br]

Add spinlock around DOMAINCFG acccess.

sys/riscv/vmm/vmm_aplic.c

180

Do you want to check the return value here?

from the spec the write is ignored if value written is not an active interrupt source number in the domain
https://github.com/riscv/riscv-aia/releases/download/0.2-draft.24/riscv-interrupts-024.pdf

304

Indeed. Added!

[markj]

sys/riscv/vmm/vmm_aplic.c

157

Why not just

if ((irq->sourcecfg & SOURCECFG_SM_M) != SOURCECFG_SM_INACTIVE) {
    if (enabled)
        ...
}

?

178

This change is required to avoid UB.

180

This would be useful to mention in a comment, along with a (void) cast for the aplic_set_enabled() call.

[br]

Address @markj comments. Thanks, Mark!