Re: [PATCH v2 26/39] xen/riscv: add guest store emulation for trapped MMIO accesses

[Baptiste Le Duc <baptiste.le-duc@xxxxxxxxxx>]

> Extend the guest page fault handler with store emulation to support MMIO
> write accesses.
> 
> The instruction decode mirrors emulate_load() and, like it, is adapted
> from Linux's KVM RISC-V implementation. As with the load path, the
> completion is synchronous through try_handle_mmio() rather than KVM's
> userspace exit/return split, since Xen's MMIO handlers run in the
> hypervisor. Faults taken while re-reading the trapped instruction are
> handled by decode_ldst_insn(), shared with the load path.
> 
> When a guest store instruction faults, the trapped instruction is decoded
> using HTINST or, if unavailable, fetched via unprivileged access. At the
Nit: commit message restates the HTINST-or-unprivileged-fetch decode
mechanism, which is already described in the prep patch introducing
decode_ldst_insn()/insn_fetch_faulted(), and isn't repeated in
emulate_load()'s commit message. Suggest trimming for symmetry with the
load commit, e.g.:

  When a guest store instruction faults, the trapped instruction is
  decoded via decode_ldst_insn(), shared with the load path. At the
  moment only virtual interrupt controller (vINTC) traps are expected to
  occur, since it is currently the only backend registered with the MMIO
  handler dispatch, so in practice the store is emulated via the vINTC
  backend.

-- 
Baptiste Le Duc <baptiste.le-duc@xxxxxxxxxx>