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Date:   Mon, 12 Dec 2022 10:37:16 -0800
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Subject: [Patch v4 09/13] KVM: x86: hyper-v: Add extended hypercall support in Hyper-v
From:   Vipin Sharma <vipinsh@google.com>
To:     seanjc@google.com, pbonzini@redhat.com, vkuznets@redhat.com,
        dmatlack@google.com
Cc:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        Vipin Sharma <vipinsh@google.com>
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Add support for extended hypercall in Hyper-v. Hyper-v TLFS 6.0b
describes hypercalls above call code 0x8000 as extended hypercalls.

A Hyper-v hypervisor's guest VM finds availability of extended
hypercalls via CPUID.0x40000003.EBX BIT(20). If the bit is set then the
guest can call extended hypercalls.

All extended hypercalls will exit to userspace by default. This allows
for easy support of future hypercalls without being dependent on KVM
releases.

If there will be need to process the hypercall in KVM instead of
userspace then KVM can create a capability which userspace can query to
know which hypercalls can be handled by the KVM and enable handling
of those hypercalls.

Signed-off-by: Vipin Sharma <vipinsh@google.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>

---
 arch/x86/kvm/hyperv.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 2eb68533d188..e232ea578ba5 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -43,6 +43,24 @@
 
 #define KVM_HV_MAX_SPARSE_VCPU_SET_BITS DIV_ROUND_UP(KVM_MAX_VCPUS, HV_VCPUS_PER_SPARSE_BANK)
 
+/*
+ * As per Hyper-V TLFS, extended hypercalls start from 0x8001
+ * (HvExtCallQueryCapabilities). Response of this hypercalls is a 64 bit value
+ * where each bit tells which extended hypercall is available besides
+ * HvExtCallQueryCapabilities.
+ *
+ * 0x8001 - First extended hypercall, HvExtCallQueryCapabilities, no bit
+ * assigned.
+ *
+ * 0x8002 - Bit 0
+ * 0x8003 - Bit 1
+ * ..
+ * 0x8041 - Bit 63
+ *
+ * Therefore, HV_EXT_CALL_MAX = 0x8001 + 64
+ */
+#define HV_EXT_CALL_MAX (HV_EXT_CALL_QUERY_CAPABILITIES + 64)
+
 static void stimer_mark_pending(struct kvm_vcpu_hv_stimer *stimer,
 				bool vcpu_kick);
 
@@ -2429,6 +2447,9 @@ static bool hv_check_hypercall_access(struct kvm_vcpu_hv *hv_vcpu, u16 code)
 	case HVCALL_SEND_IPI:
 		return hv_vcpu->cpuid_cache.enlightenments_eax &
 			HV_X64_CLUSTER_IPI_RECOMMENDED;
+	case HV_EXT_CALL_QUERY_CAPABILITIES ... HV_EXT_CALL_MAX:
+		return hv_vcpu->cpuid_cache.features_ebx &
+				HV_ENABLE_EXTENDED_HYPERCALLS;
 	default:
 		break;
 	}
@@ -2582,6 +2603,12 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
 		}
 		goto hypercall_userspace_exit;
 	}
+	case HV_EXT_CALL_QUERY_CAPABILITIES ... HV_EXT_CALL_MAX:
+		if (unlikely(hc.fast)) {
+			ret = HV_STATUS_INVALID_PARAMETER;
+			break;
+		}
+		goto hypercall_userspace_exit;
 	default:
 		ret = HV_STATUS_INVALID_HYPERCALL_CODE;
 		break;
@@ -2741,6 +2768,7 @@ int kvm_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid,
 
 			ent->ebx |= HV_POST_MESSAGES;
 			ent->ebx |= HV_SIGNAL_EVENTS;
+			ent->ebx |= HV_ENABLE_EXTENDED_HYPERCALLS;
 
 			ent->edx |= HV_X64_HYPERCALL_XMM_INPUT_AVAILABLE;
 			ent->edx |= HV_FEATURE_FREQUENCY_MSRS_AVAILABLE;
-- 
2.39.0.rc1.256.g54fd8350bd-goog