[PATCH 08/18] KVM: x86: hyper-v: Exit on StartVirtualProcessor and GetVpIndexFromApicId hcalls

Nicolas Saenz Julienne
2024-06-09T15:55:27Z

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