# Re: \[PATCH V6 5/8\] x86/hyperv: Add Write/Read MSR registers via ghcb page

- From: Tom Lendacky \<thomas.lendacky@amd.com\>
- Date: 2021-09-30 18:27:31 
- List: netdev
- Page: https://ratatoskr.run/netdev/2021/09/1527441
- Thread: https://ratatoskr.run/linux-arch/2021/09/1527043/t.md

```text
On 9/30/21 8:05 AM, Tianyu Lan wrote:
> From: Tianyu Lan <redacted>
>

...

> diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
> index 9f90f460a28c..dd7f37de640b 100644
> --- a/arch/x86/kernel/sev-shared.c
> +++ b/arch/x86/kernel/sev-shared.c
> @@ -94,10 +94,9 @@ static void vc_finish_insn(struct es_em_ctxt *ctxt)
>   	ctxt->regs->ip += ctxt->insn.length;
>   }
>   
> -static enum es_result sev_es_ghcb_hv_call(struct ghcb *ghcb,
> -					  struct es_em_ctxt *ctxt,
> -					  u64 exit_code, u64 exit_info_1,
> -					  u64 exit_info_2)
> +enum es_result sev_es_ghcb_hv_call_simple(struct ghcb *ghcb,
> +				   u64 exit_code, u64 exit_info_1,
> +				   u64 exit_info_2)
>   {
>   	enum es_result ret;
>   
> @@ -109,29 +108,45 @@ static enum es_result sev_es_ghcb_hv_call(struct ghcb *ghcb,
>   	ghcb_set_sw_exit_info_1(ghcb, exit_info_1);
>   	ghcb_set_sw_exit_info_2(ghcb, exit_info_2);
>   
> -	sev_es_wr_ghcb_msr(__pa(ghcb));
>   	VMGEXIT();
>   
> -	if ((ghcb->save.sw_exit_info_1 & 0xffffffff) == 1) {
> -		u64 info = ghcb->save.sw_exit_info_2;
> -		unsigned long v;
> -
> -		info = ghcb->save.sw_exit_info_2;
> -		v = info & SVM_EVTINJ_VEC_MASK;
> -
> -		/* Check if exception information from hypervisor is sane. */
> -		if ((info & SVM_EVTINJ_VALID) &&
> -		    ((v == X86_TRAP_GP) || (v == X86_TRAP_UD)) &&
> -		    ((info & SVM_EVTINJ_TYPE_MASK) == SVM_EVTINJ_TYPE_EXEPT)) {
> -			ctxt->fi.vector = v;
> -			if (info & SVM_EVTINJ_VALID_ERR)
> -				ctxt->fi.error_code = info >> 32;
> -			ret = ES_EXCEPTION;
> -		} else {
> -			ret = ES_VMM_ERROR;
> -		}
> -	} else {
> +	if ((ghcb->save.sw_exit_info_1 & 0xffffffff) == 1)

Really, any non-zero value indicates an error, so this should be:

	if (ghcb->save.sw_exit_info_1 & 0xffffffff)

> +		ret = ES_VMM_ERROR;
> +	else
>   		ret = ES_OK;
> +
> +	return ret;
> +}
> +
> +static enum es_result sev_es_ghcb_hv_call(struct ghcb *ghcb,
> +				   struct es_em_ctxt *ctxt,
> +				   u64 exit_code, u64 exit_info_1,
> +				   u64 exit_info_2)
> +{
> +	unsigned long v;
> +	enum es_result ret;
> +	u64 info;
> +
> +	sev_es_wr_ghcb_msr(__pa(ghcb));
> +
> +	ret = sev_es_ghcb_hv_call_simple(ghcb, exit_code, exit_info_1,
> +					 exit_info_2);
> +	if (ret == ES_OK)
> +		return ret;
> +

And then here, the explicit check for 1 should be performed and if not 1, then return ES_VMM_ERROR. If it is 1, then check the event injection values.

Thanks,
Tom

> +	info = ghcb->save.sw_exit_info_2;
> +	v = info & SVM_EVTINJ_VEC_MASK;
> +
> +	/* Check if exception information from hypervisor is sane. */
> +	if ((info & SVM_EVTINJ_VALID) &&
> +	    ((v == X86_TRAP_GP) || (v == X86_TRAP_UD)) &&
> +	    ((info & SVM_EVTINJ_TYPE_MASK) == SVM_EVTINJ_TYPE_EXEPT)) {
> +		ctxt->fi.vector = v;
> +		if (info & SVM_EVTINJ_VALID_ERR)
> +			ctxt->fi.error_code = info >> 32;
> +		ret = ES_EXCEPTION;
> +	} else {
> +		ret = ES_VMM_ERROR;
>   	}
>   
>   	return ret;
```