linux-kernel - Re: [PATCHv3 4/4] x86/sev-es: Use insn_decode

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Date:   Mon, 29 Nov 2021 15:31:52 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Joerg Roedel <jroedel@...e.de>
Cc:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCHv3 4/4] x86/sev-es: Use insn_decode_mmio() for MMIO
 implementation

On 11/3/21 10:45 AM, Kirill A. Shutemov wrote:
> From: "Kirill A. Shutemov" <kirill@...temov.name>
> 
> Switch SEV implementation to insn_decode_mmio(). The helper is going
> to be used by TDX too.
> 
> No functional changes. It is only build-tested.
> 
> Cc: Tom Lendacky <thomas.lendacky@....com>
> Cc: Joerg Roedel <jroedel@...e.de>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Reviewed-by: Andi Kleen <ak@...ux.intel.com>
> Reviewed-by: Tony Luck <tony.luck@...el.com>
> ---
>   arch/x86/kernel/sev.c | 171 ++++++++++--------------------------------
>   1 file changed, 40 insertions(+), 131 deletions(-)
> 
> diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
> index a6895e440bc3..8fea7ea67c67 100644
> --- a/arch/x86/kernel/sev.c
> +++ b/arch/x86/kernel/sev.c

...

>   		break;
> +	case MMIO_READ_ZERO_EXTEND:
> +		ret = vc_do_mmio(ghcb, ctxt, bytes, true);
> +		if (ret)
> +			break;
> +

Can you keep the "/* Zero extend based on operand size */" comment here 
much like you do below with the sign extended operation below.

Thanks,
Tom

> +		memset(reg_data, 0, insn->opnd_bytes);
> +		memcpy(reg_data, ghcb->shared_buffer, bytes);
> +		break;
> +	case MMIO_READ_SIGN_EXTEND:
> +		ret = vc_do_mmio(ghcb, ctxt, bytes, true);
> +		if (ret)
> +			break;
>   
> -		/* MOVS instruction */
> -	case 0xa4:
> -		bytes = 1;
> -		fallthrough;
> -	case 0xa5:
> -		if (!bytes)
> -			bytes = insn->opnd_bytes;
> +		if (bytes == 1) {
> +			u8 *val = (u8 *)ghcb->shared_buffer;
>   
> -		ret = vc_handle_mmio_movs(ctxt, bytes);
> +			sign_byte = (*val & 0x80) ? 0xff : 0x00;
> +		} else {
> +			u16 *val = (u16 *)ghcb->shared_buffer;
> +
> +			sign_byte = (*val & 0x8000) ? 0xff : 0x00;
> +		}
> +
> +		/* Sign extend based on operand size */
> +		memset(reg_data, sign_byte, insn->opnd_bytes);
> +		memcpy(reg_data, ghcb->shared_buffer, bytes);
>   		break;
> -		/* Two-Byte Opcodes */
> -	case 0x0f:
> -		ret = vc_handle_mmio_twobyte_ops(ghcb, ctxt);
> +	case MMIO_MOVS:
> +		ret = vc_handle_mmio_movs(ctxt, bytes);
>   		break;
>   	default:
>   		ret = ES_UNSUPPORTED;
> +		break;
>   	}
>   
>   	return ret;
>