[PATCH] KVM: VMX: Conditionally reload debug register 6

Avi Kivity
2009-09-01T11:40:48Z

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.

Signed-off-by: Avi Kivity <avi@redhat.com>
---
arch/x86/kvm/vmx.c | 6 ++++--
1 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 05cd554..70b0c54 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3629,7 +3629,8 @@ 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 +3732,8 @@ 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