On Mon, Nov 07, 2022, Oliver Upton wrote:
> Use RCU to safely walk the stage-2 page tables in parallel. Acquire and
> release the RCU read lock when traversing the page tables. Defer the
> freeing of table memory to an RCU callback. Indirect the calls into RCU
> and provide stubs for hypervisor code, as RCU is not available in such a
> context.
>
> The RCU protection doesn't amount to much at the moment, as readers are
> already protected by the read-write lock (all walkers that free table
> memory take the write lock). Nonetheless, a subsequent change will
> futher relax the locking requirements around the stage-2 MMU, thereby
> depending on RCU.
Two somewhat off-topic questions (because I'm curious):
1. Are there plans to enable "fast" page faults on ARM? E.g. to fixup access
faults (handle_access_fault()) and/or write-protection faults without acquiring
mmu_lock?
2. If the answer to (1) is "yes!", what's the plan to protect the lockless walks
for the RCU-less hypervisor code?
