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

- From: Tianyu Lan \<hidden\>
- Date: 2021-10-01 13:45:07 
- List: netdev
- Page: https://ratatoskr.run/netdev/2021/10/1528142
- Thread: https://ratatoskr.run/linux-arch/2021/09/1527043/t.md

```text
Hi Tom:
     Thanks for your review.

On 10/1/2021 2:27 AM, Tom Lendacky wrote:
> 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

Good suggestion. Will update.

>
>> +    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;
```