x86/apic: KVM: Use cpu_physical_id() to get APIC ID of running vCPU for AVIC

098e32cb · Sean Christopherson <[email protected]> · 2026-06-12 11:54:59 -07:00

Use cpu_physical_id() instead of default_cpu_present_to_apicid() when
getting the APIC ID of the pCPU on which a vCPU is running/loaded, as the
kernel has gone way off the rails if a vCPU is loaded on a pCPU that has
been physically removed from the system.  Even if the impossible were to
happen, the absolutely worst case scenario is that hardware will ring the
AIVC doorbell on the wrong pCPU, i.e. a severely broken system will
experience mild performance issues.

Kill off KVM's superfluous kvm_cpu_get_apicid() wrapper along with the
for-KVM export of default_cpu_present_to_apicid(), as they existed purely
for the wonky AVIC usage.

Cc: Kai Huang <[email protected]>
Cc: Yosry Ahmed <[email protected]>
Signed-off-by: Sean Christopherson <[email protected]>
Acked-by: Naveen N Rao (AMD) <[email protected]>
Reviewed-by: Kai Huang <[email protected]>
Reviewed-by: Yosry Ahmed <[email protected]>
Message-ID: <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>

Commit: 098e32cba334da0f3fa8cfd4e022ae7c72341400
Parents: 02953418

Changes

3 files changed · +3 −14

File	Status	Add	Del	Content
arch/x86/include/asm/kvm_host.h	modified	+0	−10	View file
arch/x86/kernel/apic/apic_common.c	modified	+0	−1	View file
arch/x86/kvm/svm/avic.c	modified	+3	−3	View file

arch/x86/include/asm/kvm_host.h

View file

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 9347c2b..5f6c1ce 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -2525,16 +2525,6 @@ static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu)
 	kvm_x86_call(vcpu_unblocking)(vcpu);
 }
 
-static inline int kvm_cpu_get_apicid(int mps_cpu)
-{
-#ifdef CONFIG_X86_LOCAL_APIC
-	return default_cpu_present_to_apicid(mps_cpu);
-#else
-	WARN_ON_ONCE(1);
-	return BAD_APICID;
-#endif
-}
-
 int memslot_rmap_alloc(struct kvm_memory_slot *slot, unsigned long npages);
 
 #define KVM_CLOCK_VALID_FLAGS						\

arch/x86/kernel/apic/apic_common.c

View file

diff --git a/arch/x86/kernel/apic/apic_common.c b/arch/x86/kernel/apic/apic_common.c
index 2ed3b5c..45e6b81 100644
--- a/arch/x86/kernel/apic/apic_common.c
+++ b/arch/x86/kernel/apic/apic_common.c
@@ -26,7 +26,6 @@ u32 default_cpu_present_to_apicid(int mps_cpu)
 	else
 		return BAD_APICID;
 }
-EXPORT_SYMBOL_FOR_KVM(default_cpu_present_to_apicid);
 
 /*
  * Set up the logical destination ID when the APIC operates in logical

arch/x86/kvm/svm/avic.c

View file

diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index 0726f88..58e493a 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -460,8 +460,8 @@ void avic_ring_doorbell(struct kvm_vcpu *vcpu)
 	int cpu = READ_ONCE(vcpu->cpu);
 
 	if (cpu != get_cpu()) {
-		wrmsrq(MSR_AMD64_SVM_AVIC_DOORBELL, kvm_cpu_get_apicid(cpu));
-		trace_kvm_avic_doorbell(vcpu->vcpu_id, kvm_cpu_get_apicid(cpu));
+		wrmsrq(MSR_AMD64_SVM_AVIC_DOORBELL, cpu_physical_id(cpu));
+		trace_kvm_avic_doorbell(vcpu->vcpu_id, cpu_physical_id(cpu));
 	}
 	put_cpu();
 }
@@ -1013,7 +1013,7 @@ static void __avic_vcpu_load(struct kvm_vcpu *vcpu, int cpu,
 			     enum avic_vcpu_action action)
 {
 	struct kvm_svm *kvm_svm = to_kvm_svm(vcpu->kvm);
-	int h_physical_id = kvm_cpu_get_apicid(cpu);
+	int h_physical_id = cpu_physical_id(cpu);
 	struct vcpu_svm *svm = to_svm(vcpu);
 	unsigned long flags;
 	u64 entry;