Re: [PATCH 02/60] KVM: SVM: Add support for the SEV-SNP #HV doorbell page NAE event

On 6/10/26 08:28, Tom Lendacky wrote:
> On 6/8/26 09:41, Jörg Rödel wrote:
>> From: Melody Wang <[email protected]>
>>
>> To support Restricted Injection, the SEV-SNP guest must register a doorbell
>> page for use with #HV. This is done using the #HV doorbell page NAE event.
>>
>> This event consists of four actions: GET_PREFERRED, SET, QUERY, CLEAR.
>> Implement it per the GHCB specification.
>>
>> Co-developed-by: Thomas Lendacky <[email protected]>
>> Signed-off-by: Thomas Lendacky <[email protected]>
>> Signed-off-by: Melody Wang <[email protected]>
>> Signed-off-by: Joerg Roedel <[email protected]>
>> ---
>>  arch/x86/include/uapi/asm/svm.h |  5 +++
>>  arch/x86/kvm/svm/sev.c          | 71 +++++++++++++++++++++++++++++++++
>>  arch/x86/kvm/svm/svm.c          |  3 ++
>>  arch/x86/kvm/svm/svm.h          |  2 +
>>  4 files changed, 81 insertions(+)
>>
>> diff --git a/arch/x86/include/uapi/asm/svm.h b/arch/x86/include/uapi/asm/svm.h
>> index 010a45c9f614..d84a13ac4627 100644
>> --- a/arch/x86/include/uapi/asm/svm.h
>> +++ b/arch/x86/include/uapi/asm/svm.h
>> @@ -117,6 +117,11 @@
>>  #define SVM_VMGEXIT_AP_CREATE_ON_INIT		0
>>  #define SVM_VMGEXIT_AP_CREATE			1
>>  #define SVM_VMGEXIT_AP_DESTROY			2
>> +#define SVM_VMGEXIT_HVDB_PAGE			0x80000014ull
>> +#define SVM_VMGEXIT_HVDB_GET_PREFERRED		0
>> +#define SVM_VMGEXIT_HVDB_SET			1
>> +#define SVM_VMGEXIT_HVDB_QUERY			2
>> +#define SVM_VMGEXIT_HVDB_CLEAR			3
>>  #define SVM_VMGEXIT_SNP_RUN_VMPL		0x80000018ull
>>  #define SVM_VMGEXIT_SAVIC			0x8000001aull
>>  #define SVM_VMGEXIT_SAVIC_REGISTER_GPA		0
>> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
>> index 6c6a6d663e29..b9ad1169cb2c 100644
>> --- a/arch/x86/kvm/svm/sev.c
>> +++ b/arch/x86/kvm/svm/sev.c
>> @@ -3522,6 +3522,10 @@ static int sev_es_validate_vmgexit(struct vcpu_svm *svm)
>>  		    control->exit_info_1 == control->exit_info_2)
>>  			goto vmgexit_err;
>>  		break;
>> +	case SVM_VMGEXIT_HVDB_PAGE:
>> +		if (!is_sev_snp_guest(vcpu))

I think it should also be validated that Restricted Injection is enabled
for the guest as well - either here or in the sev_snp_hv_doorbell_page()
function.

Thanks,
Tom

>> +			goto vmgexit_err;
>> +		break;
>>  	default:
>>  		reason = GHCB_ERR_INVALID_EVENT;
>>  		goto vmgexit_err;
>> @@ -4341,6 +4345,65 @@ static int snp_handle_ext_guest_req(struct vcpu_svm *svm, gpa_t req_gpa, gpa_t r
>>  	return 1; /* resume guest */
>>  }
>>  
>> +static int sev_snp_hv_doorbell_page(struct vcpu_svm *svm)
>> +{
>> +	struct kvm_vcpu *vcpu = &svm->vcpu;
>> +	struct kvm_host_map hvdb_map;
>> +	gpa_t hvdb_gpa;
>> +	u64 request;
>> +
>> +	if (!is_sev_snp_guest(vcpu))
>> +		return -EINVAL;
>> +
>> +	request = svm->vmcb->control.exit_info_1;
>> +	hvdb_gpa = svm->vmcb->control.exit_info_2;
>> +
>> +	switch (request) {
>> +	case SVM_VMGEXIT_HVDB_GET_PREFERRED:
>> +		ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, ~0ULL);
>> +		break;
>> +	case SVM_VMGEXIT_HVDB_SET:
>> +		svm->sev_es.hvdb_gpa = INVALID_PAGE;
>> +
>> +		if (!PAGE_ALIGNED(hvdb_gpa)) {
>> +			vcpu_unimpl(vcpu, "vmgexit: unaligned #HV doorbell page address [%#llx] from guest\n",
>> +				    hvdb_gpa);
>> +			return -EINVAL;
>> +		}
>> +
>> +		if (!page_address_valid(vcpu, hvdb_gpa)) {
>> +			vcpu_unimpl(vcpu, "vmgexit: invalid #HV doorbell page address [%#llx] from guest\n",
>> +				    hvdb_gpa);
>> +			return -EINVAL;
>> +		}
>> +
>> +		/* Map and unmap the GPA just to be sure the GPA is valid */
>> +		if (kvm_vcpu_map(vcpu, gpa_to_gfn(hvdb_gpa), &hvdb_map)) {
>> +			vcpu_unimpl(vcpu, "vmgexit: error mapping #HV doorbell page [%#llx] from guest\n",
>> +				    hvdb_gpa);
>> +			return -EINVAL;
>> +		}
>> +		kvm_vcpu_unmap(vcpu, &hvdb_map);
>> +
>> +		svm->sev_es.hvdb_gpa = hvdb_gpa;
>> +		fallthrough;
>> +	case SVM_VMGEXIT_HVDB_QUERY:
>> +		ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, svm->sev_es.hvdb_gpa);
>> +		break;
>> +	case SVM_VMGEXIT_HVDB_CLEAR:
>> +		svm->sev_es.hvdb_gpa = INVALID_PAGE;
>> +		break;
>> +	default:
>> +		svm->sev_es.hvdb_gpa = INVALID_PAGE;
>> +
>> +		vcpu_unimpl(vcpu, "vmgexit: invalid #HV doorbell page request [%#llx] from guest\n",
>> +			    request);
>> +		return -EINVAL;
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>>  static int sev_handle_vmgexit_msr_protocol(struct vcpu_svm *svm)
>>  {
>>  	struct vmcb_control_area *control = &svm->vmcb->control;
>> @@ -4617,6 +4680,14 @@ int sev_handle_vmgexit(struct kvm_vcpu *vcpu)
>>  	case SVM_VMGEXIT_EXT_GUEST_REQUEST:
>>  		ret = snp_handle_ext_guest_req(svm, control->exit_info_1, control->exit_info_2);
>>  		break;
>> +	case SVM_VMGEXIT_HVDB_PAGE:
>> +		if (sev_snp_hv_doorbell_page(svm)) {
>> +			ghcb_set_sw_exit_info_1(svm->sev_es.ghcb, 2);
>> +			ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, GHCB_ERR_INVALID_INPUT);
>> +		}
>> +
>> +		ret = 1;
>> +		break;
>>  	case SVM_VMGEXIT_UNSUPPORTED_EVENT:
>>  		vcpu_unimpl(vcpu,
>>  			    "vmgexit: unsupported event - exit_info_1=%#llx, exit_info_2=%#llx\n",
>> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
>> index e02a38da5296..7981e7583384 100644
>> --- a/arch/x86/kvm/svm/svm.c
>> +++ b/arch/x86/kvm/svm/svm.c
>> @@ -1277,6 +1277,9 @@ static void __svm_vcpu_reset(struct kvm_vcpu *vcpu)
>>  
>>  	svm->nmi_masked = false;
>>  	svm->awaiting_iret_completion = false;
>> +
>> +	if (is_sev_es_guest(vcpu))
> 
> Shouldn't this be is_sev_snp_guest() ?
> 
> Thanks,
> Tom
> 
>> +		svm->sev_es.hvdb_gpa = INVALID_PAGE;
>>  }
>>  
>>  static void svm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
>> index 5137416be593..fb956c37c941 100644
>> --- a/arch/x86/kvm/svm/svm.h
>> +++ b/arch/x86/kvm/svm/svm.h
>> @@ -270,6 +270,8 @@ struct vcpu_sev_es_state {
>>  	gpa_t snp_vmsa_gpa;
>>  	bool snp_ap_waiting_for_reset;
>>  	bool snp_has_guest_vmsa;
>> +
>> +	gpa_t hvdb_gpa;
>>  };
>>  
>>  struct vcpu_svm {
>