Re: [PATCH 3/7] KVM: x86 emulator: introduce NoWrite flag

[Gleb Natapov <gleb@redhat.com>]

On Sat, Dec 22, 2012 at 02:26:53PM +0200, Avi Kivity wrote:
> Instead of disabling writeback via OP_NONE, just specify NoWrite.
> 
> Signed-off-by: Avi Kivity <avi.kivity@gmail.com>
> ---
>  arch/x86/kvm/emulate.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index 9859df6..9dfbd07 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -150,6 +150,7 @@
>  #define Unaligned   ((u64)1 << 42)  /* Explicitly unaligned (e.g. MOVDQU) */
>  #define Avx         ((u64)1 << 43)  /* Advanced Vector Extensions */
>  #define Fastop      ((u64)1 << 44)  /* Use opcode::u.fastop */
> +#define NoWrite     ((u64)1 << 45)  /* No writeback */
>  
>  #define X2(x...) x, x
>  #define X3(x...) X2(x), x
> @@ -1584,6 +1585,9 @@ static int writeback(struct x86_emulate_ctxt *ctxt)
>  {
>  	int rc;
>  
> +	if (ctxt->d & NoWrite)
> +		return X86EMUL_CONTINUE;
> +
Why not make it Dst flag and set dst.type to OP_NONE during decoding
instead of this special case?

>  	switch (ctxt->dst.type) {
>  	case OP_REG:
>  		write_register_operand(&ctxt->dst);
> -- 
> 1.7.11.7

--
			Gleb.