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

[Tom Lendacky <thomas.lendacky@amd.com>]

On 6/8/26 09:41, Jörg Rödel wrote:
> From: Melody Wang <huibo.wang@amd.com>
> 
> 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 <thomas.lendacky@amd.com>
> Signed-off-by: Thomas Lendacky <thomas.lendacky@amd.com>
> Signed-off-by: Melody Wang <huibo.wang@amd.com>
> Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
> ---
>  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))
> +			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 {