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

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

On 9/18/26 11:16 AM, Baptiste Le Duc wrote:
> > 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.
I will update the commit message.

Thanks.

~ Oleksii