Re: [XEN v10 2/4] xen/arm64: io: Support instructions (for which ISS is not valid) on emulated MMIO region using MMIO/ioreq handler

[Julien Grall <julien@xxxxxxx>]

Hi,

On 10/03/2022 17:44, Ayan Kumar Halder wrote:
> When an instruction is trapped in Xen due to translation fault, Xen
> checks if the ISS is invalid (for data abort) or it is an instruction
> abort. If so, Xen tries to resolve the translation fault using p2m page
> tables. In case of data abort, Xen will try to map the mmio region to
> the guest (ie tries to emulate the mmio region).
>
> If the ISS is not valid and it is a data abort, then Xen tries to
> decode the instruction. In case of ioreq, Xen  saves the decoding state,
> rn and imm9 to vcpu_io. Whenever the vcpu handles the ioreq successfully,
> it will read the decoding state to determine if the instruction decoded
> was a ldr/str post indexing (ie INSTR_LDR_STR_POSTINDEXING). If so, it
> uses these details to post increment rn.
>
> In case of mmio handler, if the mmio operation was successful, then Xen
> retrives the decoding state, rn and imm9. For state ==
> INSTR_LDR_STR_POSTINDEXING, Xen will update rn.
>
> If there is an error encountered while decoding/executing the instruction,
> Xen will forward the abort to the guest.
>
> Also, the logic to infer the type of instruction has been moved from
> try_handle_mmio() to try_decode_instruction() which is called before.
> try_handle_mmio() is solely responsible for handling the mmio operation.
>
> Signed-off-by: Ayan Kumar Halder <ayankuma@xxxxxxxxxx>
Acked-by: Julien Grall <jgrall@xxxxxxxxxx>

Cheers,

--
Julien Grall