diff mbox series

[v2,1/9] KVM: x86: Short-circuit all kvm_lapic_set_base() if MSR value isn't changing

Message ID 20241101183555.1794700-2-seanjc@google.com (mailing list archive)
State New
Headers show
Series KVM: x86: Clean up MSR_IA32_APICBASE_BASE code | expand

Commit Message

Sean Christopherson Nov. 1, 2024, 6:35 p.m. UTC 
Do nothing in kvm_lapic_set_base() if the APIC base MSR value is the same
as the current value.  All flows except the handling of the base address
explicitly take effect if and only if relevant bits are changing.

For the base address, invoking kvm_lapic_set_base() before KVM initializes
the base to APIC_DEFAULT_PHYS_BASE during vCPU RESET would be a KVM bug,
i.e. KVM _must_ initialize apic->base_address before exposing the vCPU (to
userspace or KVM at-large).

Note, the inhibit is intended to be set if the base address is _changed_
from the default, i.e. is also covered by the RESET behavior.

Reviewed-by: Kai Huang <kai.huang@intel.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Link: https://lore.kernel.org/r/20241009181742.1128779-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/lapic.c | 3 +++
 1 file changed, 3 insertions(+)
diff mbox series

Patch

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 65412640cfc7..8fe63f719254 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2582,6 +2582,9 @@  void kvm_lapic_set_base(struct kvm_vcpu *vcpu, u64 value)
 	u64 old_value = vcpu->arch.apic_base;
 	struct kvm_lapic *apic = vcpu->arch.apic;
 
+	if (old_value == value)
+		return;
+
 	vcpu->arch.apic_base = value;
 
 	if ((old_value ^ value) & MSR_IA32_APICBASE_ENABLE)