linux-kernel - [PATCH v2 2/6] KVM: x86: hyper-v: Add extended hypercall support in Hyper-v

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Date:   Mon, 21 Nov 2022 15:40:22 -0800
From:   Vipin Sharma <vipinsh@...gle.com>
To:     seanjc@...gle.com, pbonzini@...hat.com, vkuznets@...hat.com,
        dmatlack@...gle.com
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Vipin Sharma <vipinsh@...gle.com>
Subject: [PATCH v2 2/6] KVM: x86: hyper-v: Add extended hypercall support in Hyper-v

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@...gle.com>
---
 arch/x86/kvm/hyperv.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 0b6964ed2e66..8551ef495cc9 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -43,6 +43,12 @@
 
 #define KVM_HV_MAX_SPARSE_VCPU_SET_BITS DIV_ROUND_UP(KVM_MAX_VCPUS, HV_VCPUS_PER_SPARSE_BANK)
 
+/*
+ * The TLFS carves out 64 possible extended hypercalls, numbered sequentially
+ * after the base capabilities extended hypercall.
+ */
+#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);
 
@@ -2411,6 +2417,9 @@ 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;
 	}
@@ -2564,6 +2573,12 @@ 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;
@@ -2722,6 +2737,7 @@ 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;
-- 
2.38.1.584.g0f3c55d4c2-goog