[PATCH 02/60] KVM: SVM: Add support for the SEV-SNP #HV doorbell page NAE event
Tom Lendacky
thomas.lendacky at amd.com
Wed Jun 10 08:05:37 PDT 2026
On 6/10/26 08:28, Tom Lendacky wrote:
> On 6/8/26 09:41, Jörg Rödel wrote:
>> From: Melody Wang <huibo.wang at 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 at amd.com>
>> Signed-off-by: Thomas Lendacky <thomas.lendacky at amd.com>
>> Signed-off-by: Melody Wang <huibo.wang at amd.com>
>> Signed-off-by: Joerg Roedel <joerg.roedel at 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))
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 {
>
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