Commit e8a48342 authored by Avi Kivity's avatar Avi Kivity
Browse files

KVM: VMX: Conditionally reload debug register 6 



Only reload debug register 6 if we're running with the guest's
debug registers.  Saves around 150 cycles from the guest lightweight
exit path.

dr6 contains a couple of bits that are updated on #DB, so intercept
that unconditionally and update those bits then.

Signed-off-by: default avatarAvi Kivity <avi@redhat.com>
Signed-off-by: default avatarMarcelo Tosatti <mtosatti@redhat.com>
parent 3d53c27d

arch/x86/kvm/vmx.c

+9 −5
Original line number Diff line number Diff line
@@ -540,10 +540,12 @@ static void update_exception_bitmap(struct kvm_vcpu *vcpu) 
	eb = (1u << PF_VECTOR) | (1u << UD_VECTOR) | (1u << MC_VECTOR);

	if (!vcpu->fpu_active)

		eb |= 1u << NM_VECTOR;

	if (vcpu->guest_debug & KVM_GUESTDBG_ENABLE) {

		if (vcpu->guest_debug &

		    (KVM_GUESTDBG_SINGLESTEP | KVM_GUESTDBG_USE_HW_BP))

	/*

	 * Unconditionally intercept #DB so we can maintain dr6 without

	 * reading it every exit.

	 */

	eb |= 1u << DB_VECTOR;

	if (vcpu->guest_debug & KVM_GUESTDBG_ENABLE) {

		if (vcpu->guest_debug & KVM_GUESTDBG_USE_SW_BP)

			eb |= 1u << BP_VECTOR;

	}
@@ -3632,6 +3634,7 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run) 
	 */

	vmcs_writel(HOST_CR0, read_cr0());



	if (vcpu->arch.switch_db_regs)

		set_debugreg(vcpu->arch.dr6, 6);



	asm(
@@ -3734,6 +3737,7 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run) 
				  | (1 << VCPU_EXREG_PDPTR));

	vcpu->arch.regs_dirty = 0;



	if (vcpu->arch.switch_db_regs)

		get_debugreg(vcpu->arch.dr6, 6);



	vmx->idt_vectoring_info = vmcs_read32(IDT_VECTORING_INFO_FIELD);

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