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From: Nicolas Saenz Julienne <nsaenz@amazon.com>
To: <linux-kernel@vger.kernel.org>, <kvm@vger.kernel.org>
CC: <pbonzini@redhat.com>, <seanjc@google.com>, <vkuznets@redhat.com>,
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	<x86@kernel.org>, <amoorthy@google.com>
Subject: [PATCH 08/18] KVM: x86: hyper-v: Exit on StartVirtualProcessor and GetVpIndexFromApicId hcalls
Date: Sun, 9 Jun 2024 15:49:37 +0000
Message-ID: <20240609154945.55332-9-nsaenz@amazon.com>
In-Reply-To: <20240609154945.55332-1-nsaenz@amazon.com>
References: <20240609154945.55332-1-nsaenz@amazon.com>
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Both HvCallStartVirtualProcessor and GetVpIndexFromApicId are used as
part of the Hyper-V VSM CPU bootstrap process, and requires VTL
awareness, as such handle the hypercall in user-space. Also, expose the
ad-hoc CPUID bit.

Note that these hypercalls aren't necessary on Hyper-V guests that don't
enable VSM.

Signed-off-by: Nicolas Saenz Julienne <nsaenz@amazon.com>
---
 Documentation/virt/kvm/api.rst    | 11 +++++++++++
 arch/x86/kvm/hyperv.c             |  7 +++++++
 include/asm-generic/hyperv-tlfs.h |  1 +
 3 files changed, 19 insertions(+)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 05b01b00a395c..161a772c23c6a 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -8941,3 +8941,14 @@ This CPUID indicates that KVM supports HvGetVpRegisters and HvSetVpRegisters.
 Currently, it is only used in conjunction with HV_ACCESS_VSM, and immediately
 exits to userspace with KVM_EXIT_HYPERV_HCALL as the reason. Userspace is
 expected to complete the hypercall before resuming execution.
+
+10.3 HV_START_VIRTUAL_PROCESSOR
+-------------------------------
+
+:Location: CPUID.40000003H:EBX[bit 21]
+
+This CPUID indicates that KVM supports HvCallStartVirtualProcessor and
+HvCallGetVpIndexFromApicId. Currently, it is only used in conjunction with
+HV_ACCESS_VSM, and immediately exits to userspace with KVM_EXIT_HYPERV_HCALL as
+the reason. Userspace is expected to complete the hypercall before resuming
+execution.
diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index cbe2aca52514b..dd64f41dc835d 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -2556,6 +2556,10 @@ static bool hv_check_hypercall_access(struct kvm_vcpu_hv *hv_vcpu, u16 code)
 	case HVCALL_SET_VP_REGISTERS:
 		return hv_vcpu->cpuid_cache.features_ebx &
 			HV_ACCESS_VP_REGISTERS;
+	case HVCALL_START_VP:
+	case HVCALL_GET_VP_ID_FROM_APIC_ID:
+		return hv_vcpu->cpuid_cache.features_ebx &
+			HV_START_VIRTUAL_PROCESSOR;
 	case HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST_EX:
 	case HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE_EX:
 		if (!(hv_vcpu->cpuid_cache.enlightenments_eax &
@@ -2743,6 +2747,8 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
 	case HVCALL_GET_VP_REGISTERS:
 	case HVCALL_SET_VP_REGISTERS:
 	case HVCALL_TRANSLATE_VIRTUAL_ADDRESS:
+	case HVCALL_START_VP:
+	case HVCALL_GET_VP_ID_FROM_APIC_ID:
 		goto hypercall_userspace_exit;
 	default:
 		ret = HV_STATUS_INVALID_HYPERCALL_CODE;
@@ -2916,6 +2922,7 @@ int kvm_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid,
 			ent->ebx |= HV_SIGNAL_EVENTS;
 			ent->ebx |= HV_ENABLE_EXTENDED_HYPERCALLS;
 			ent->ebx |= HV_ACCESS_VP_REGISTERS;
+			ent->ebx |= HV_START_VIRTUAL_PROCESSOR;
 
 			ent->edx |= HV_X64_HYPERCALL_XMM_INPUT_AVAILABLE;
 			ent->edx |= HV_X64_HYPERCALL_XMM_OUTPUT_AVAILABLE;
diff --git a/include/asm-generic/hyperv-tlfs.h b/include/asm-generic/hyperv-tlfs.h
index 57c791c555861..e24b88ec4ec00 100644
--- a/include/asm-generic/hyperv-tlfs.h
+++ b/include/asm-generic/hyperv-tlfs.h
@@ -92,6 +92,7 @@
 #define HV_ACCESS_VSM				BIT(16)
 #define HV_ACCESS_VP_REGISTERS			BIT(17)
 #define HV_ENABLE_EXTENDED_HYPERCALLS		BIT(20)
+#define HV_START_VIRTUAL_PROCESSOR		BIT(21)
 #define HV_ISOLATION				BIT(22)
 
 /*
-- 
2.40.1