Re: [Xen-devel] [PATCH RFC V4 1/5] xen: Emulate with no writes

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 04.08.14 at 13:30, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
> --- a/xen/arch/x86/hvm/emulate.c
> +++ b/xen/arch/x86/hvm/emulate.c
> @@ -688,6 +688,51 @@ static int hvmemul_write(
>      return X86EMUL_OKAY;
>  }
>  
> +static int hvmemul_write_discard(
> +    enum x86_segment seg,
> +    unsigned long offset,
> +    void *p_data,
> +    unsigned int bytes,
> +    struct x86_emulate_ctxt *ctxt)
> +{
> +    /* Discarding the write. */
> +    return X86EMUL_OKAY;
> +}

While this one is okay, ...

> +static int hvmemul_rep_ins_discard(
> +    uint16_t src_port,
> +    enum x86_segment dst_seg,
> +    unsigned long dst_offset,
> +    unsigned int bytes_per_rep,
> +    unsigned long *reps,
> +    struct x86_emulate_ctxt *ctxt)
> +{
> +    return X86EMUL_OKAY;
> +}
> +
> +static int hvmemul_rep_movs_discard(
> +   enum x86_segment src_seg,
> +   unsigned long src_offset,
> +   enum x86_segment dst_seg,
> +   unsigned long dst_offset,
> +   unsigned int bytes_per_rep,
> +   unsigned long *reps,
> +   struct x86_emulate_ctxt *ctxt)
> +{
> +    return X86EMUL_OKAY;
> +}

... these don't seem to be: I don't think you can just drop the other
half of the operation (i.e. the port or MMIO read).

Jan


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