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: Avi Kivity <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index eec0412..f482100 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -540,10 +540,12 @@
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;
}
@@ -3632,7 +3634,8 @@
*/
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 */
@@ -3734,7 +3737,8 @@
| (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)