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: Avi Kivity <avi@xxxxxxxxxx> --- v2: trap #DB so we maintain the TF related bits of DR7. arch/x86/kvm/vmx.c | 14 +++++++++----- 1 files changed, 9 insertions(+), 5 deletions(-) diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index 05cd554..d4be978 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -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; + /* + * 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_SINGLESTEP | KVM_GUESTDBG_USE_HW_BP)) - eb |= 1u << DB_VECTOR; if (vcpu->guest_debug & KVM_GUESTDBG_USE_SW_BP) eb |= 1u << BP_VECTOR; } @@ -3629,7 +3631,8 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu) */ vmcs_writel(HOST_CR0, read_cr0()); - set_debugreg(vcpu->arch.dr6, 6); + if (vcpu->arch.switch_db_regs) + set_debugreg(vcpu->arch.dr6, 6); asm( /* Store host registers */ @@ -3731,7 +3734,8 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu) | (1 << VCPU_EXREG_PDPTR)); vcpu->arch.regs_dirty = 0; - get_debugreg(vcpu->arch.dr6, 6); + if (vcpu->arch.switch_db_regs) + get_debugreg(vcpu->arch.dr6, 6); vmx->idt_vectoring_info = vmcs_read32(IDT_VECTORING_INFO_FIELD); if (vmx->rmode.irq.pending) -- 1.6.4.1 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html