linux-kernel - Re: [RFC PATCH] x86/insn: support decode MOVSXD instruction for MMIO

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Message-ID: <17b65c2a-69a8-6348-da64-641d34be122e@amd.com>
Date:   Wed, 29 Mar 2023 08:49:24 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Wu Zongyong <wuzongyong@...ux.alibaba.com>, tglx@...utronix.de,
        mingo@...hat.com, dave.hansen@...ux.intel.com, x86@...nel.org,
        linux-kernel@...r.kernel.org
Cc:     tony.luck@...el.com, kirill.shutemov@...ux.intel.com,
        wutu.xq2@...ux.alibaba.com
Subject: Re: [RFC PATCH] x86/insn: support decode MOVSXD instruction for MMIO

On 3/28/23 21:59, Wu Zongyong wrote:
> It seems MOVSXD which opcode is 0x63 is not handled, support
> to decode it in insn_decode_mmio().

Aren't there some caveats to worry about with this instruction based on 
the presence of the REX prefix 64-bit operand size bit? Sometimes it can 
be a sign extended and sometimes it can be a zero extended.

Thanks,
Tom

> 
> Signed-off-by: Wu Zongyong <wuzongyong@...ux.alibaba.com>
> ---
>   arch/x86/lib/insn-eval.c | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
> index 558a605929db..db6f93bad219 100644
> --- a/arch/x86/lib/insn-eval.c
> +++ b/arch/x86/lib/insn-eval.c
> @@ -1607,6 +1607,10 @@ enum insn_mmio_type insn_decode_mmio(struct insn *insn, int *bytes)
>   		return INSN_MMIO_DECODE_FAILED;
>   
>   	switch (insn->opcode.bytes[0]) {
> +	case 0x63: /* MOVSXD r64, m32 */
> +		*bytes = 4;
> +		type = INSN_MMIO_READ_SIGN_EXTEND;
> +		break;
>   	case 0x88: /* MOV m8,r8 */
>   		*bytes = 1;
>   		fallthrough;