[PATCH 5/5] KVM: x86: BSP in MSR_IA32_APICBASE is writable

[Nadav Amit <namit@cs.technion.ac.il>]

After reset, the CPU can change the BSP, which will be used upon INIT.  Reset
should return the BSP which QEMU asked for, and therefore handled accordingly.

To quote: "If the MP protocol has completed and a BSP is chosen, subsequent
INITs (either to a specific processor or system wide) do not cause the MP
protocol to be repeated."
[Intel SDM 8.4.2: MP Initialization Protocol Requirements and Restrictions]

Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
---
 arch/x86/kvm/lapic.c     | 2 --
 arch/x86/kvm/svm.c       | 2 +-
 arch/x86/kvm/vmx.c       | 2 +-
 include/linux/kvm_host.h | 7 ++++++-
 4 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 17da6fc..b0dbf68 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1498,8 +1498,6 @@ void kvm_lapic_set_base(struct kvm_vcpu *vcpu, u64 value)
 		return;
 	}
 
-	if (!kvm_vcpu_is_bsp(apic->vcpu))
-		value &= ~MSR_IA32_APICBASE_BSP;
 	vcpu->arch.apic_base = value;
 
 	/* update jump label if enable bit changes */
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 1ef4c0d..ef5bf21 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1261,7 +1261,7 @@ static struct kvm_vcpu *svm_create_vcpu(struct kvm *kvm, unsigned int id)
 
 	svm->vcpu.arch.apic_base = APIC_DEFAULT_PHYS_BASE |
 				   MSR_IA32_APICBASE_ENABLE;
-	if (kvm_vcpu_is_bsp(&svm->vcpu))
+	if (kvm_vcpu_is_reset_bsp(&svm->vcpu))
 		svm->vcpu.arch.apic_base |= MSR_IA32_APICBASE_BSP;
 
 	svm_init_osvw(&svm->vcpu);
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 8aee6db..7e370b2 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -4709,7 +4709,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 	if (!init_event) {
 		apic_base_msr.data = APIC_DEFAULT_PHYS_BASE |
 				     MSR_IA32_APICBASE_ENABLE;
-		if (kvm_vcpu_is_bsp(&vmx->vcpu))
+		if (kvm_vcpu_is_reset_bsp(&vmx->vcpu))
 			apic_base_msr.data |= MSR_IA32_APICBASE_BSP;
 		apic_base_msr.host_initiated = true;
 		kvm_set_apic_base(&vmx->vcpu, &apic_base_msr);
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 0f574eb..8365cae 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -968,11 +968,16 @@ static inline int kvm_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args)
 #endif /* CONFIG_HAVE_KVM_EVENTFD */
 
 #ifdef CONFIG_KVM_APIC_ARCHITECTURE
-static inline bool kvm_vcpu_is_bsp(struct kvm_vcpu *vcpu)
+static inline bool kvm_vcpu_is_reset_bsp(struct kvm_vcpu *vcpu)
 {
 	return vcpu->kvm->bsp_vcpu_id == vcpu->vcpu_id;
 }
 
+static inline bool kvm_vcpu_is_bsp(struct kvm_vcpu *vcpu)
+{
+	return (vcpu->arch.apic_base & MSR_IA32_APICBASE_BSP) != 0;
+}
+
 bool kvm_vcpu_compatible(struct kvm_vcpu *vcpu);
 
 #else
-- 
1.9.1