KVM: VMX: Clean up DR6 emulation

As we trap all debug register accesses, we do not need to switch real
DR6 at all. Clean up update_exception_bitmap at this chance, too.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 6 insertions, 17 deletions

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index c7b99e1f8aae..b7e812e9c299 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -579,17 +579,12 @@ static void update_exception_bitmap(struct kvm_vcpu *vcpu)
 {
         u32 eb;
 
-        eb = (1u << PF_VECTOR) | (1u << UD_VECTOR) | (1u << MC_VECTOR)
-                | (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_USE_SW_BP)
-                        eb |= 1u << BP_VECTOR;
-        }
+        eb = (1u << PF_VECTOR) | (1u << UD_VECTOR) | (1u << MC_VECTOR) |
+             (1u << NM_VECTOR) | (1u << DB_VECTOR);
+        if ((vcpu->guest_debug &
+             (KVM_GUESTDBG_ENABLE | KVM_GUESTDBG_USE_SW_BP)) ==
+            (KVM_GUESTDBG_ENABLE | KVM_GUESTDBG_USE_SW_BP))
+                eb |= 1u << BP_VECTOR;
         if (to_vmx(vcpu)->rmode.vm86_active)
                 eb = ~0;
         if (enable_ept)
@@ -3777,9 +3772,6 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
          */
         vmcs_writel(HOST_CR0, read_cr0());
 
-        if (vcpu->arch.switch_db_regs)
-                set_debugreg(vcpu->arch.dr6, 6);
-
         asm(
                 /* Store host registers */
                 "push %%"R"dx; push %%"R"bp;"
@@ -3880,9 +3872,6 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
                                   | (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);
         if (vmx->rmode.irq.pending)
                 fixup_rmode_irq(vmx);