From: Zhenzhong Duan zhenzhong.duan@intel.com
[ Upstream commit f66af9f222f08d5b11ea41c1bd6c07a0f12daa07 ]
In emulation of writing to cr8, one of the lowest four bits in TPR[3:0] is kept.
According to Intel SDM 10.8.6.1(baremetal scenario): "APIC.TPR[bits 7:4] = CR8[bits 3:0], APIC.TPR[bits 3:0] = 0";
and SDM 28.3(use TPR shadow): "MOV to CR8. The instruction stores bits 3:0 of its source operand into bits 7:4 of VTPR; the remainder of VTPR (bits 3:0 and bits 31:8) are cleared.";
and AMD's APM 16.6.4: "Task Priority Sub-class (TPS)-Bits 3 : 0. The TPS field indicates the current sub-priority to be used when arbitrating lowest-priority messages. This field is written with zero when TPR is written using the architectural CR8 register.";
so in KVM emulated scenario, clear TPR[3:0] to make a consistent behavior as in other scenarios.
This doesn't impact evaluation and delivery of pending virtual interrupts because processor does not use the processor-priority sub-class to determine which interrupts to delivery and which to inhibit.
Sub-class is used by hardware to arbitrate lowest priority interrupts, but KVM just does a round-robin style delivery.
Fixes: b93463aa59d6 ("KVM: Accelerated apic support") Signed-off-by: Zhenzhong Duan zhenzhong.duan@intel.com Reviewed-by: Sean Christopherson seanjc@google.com Message-Id: 20220210094506.20181-1-zhenzhong.duan@intel.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/kvm/lapic.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-)
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index bfed29a4c2ce..e5f92488c3cd 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -1767,10 +1767,7 @@ void kvm_set_lapic_tscdeadline_msr(struct kvm_vcpu *vcpu, u64 data)
void kvm_lapic_set_tpr(struct kvm_vcpu *vcpu, unsigned long cr8) { - struct kvm_lapic *apic = vcpu->arch.apic; - - apic_set_tpr(apic, ((cr8 & 0x0f) << 4) - | (kvm_lapic_get_reg(apic, APIC_TASKPRI) & 4)); + apic_set_tpr(vcpu->arch.apic, (cr8 & 0x0f) << 4); }
u64 kvm_lapic_get_cr8(struct kvm_vcpu *vcpu)