[PATCH 3/3] KVM: x86: simplify dr6 accessors in kvm_x86_ops

[Paolo Bonzini]

kvm_x86_ops.set_dr6 is only ever called with vcpu->arch.dr6 as the
second argument, and for both SVM and VMX the VMCB value is kept
synchronized with vcpu->arch.dr6 on #DB; we can therefore remove the
read accessor.

For the write accessor we can avoid the retpoline penalty on Intel
by accepting a NULL value and just skipping the call in that case.

Suggested-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
 arch/x86/include/asm/kvm_host.h |  1 -
 arch/x86/kvm/svm/svm.c          |  6 ------
 arch/x86/kvm/vmx/vmx.c          | 11 -----------
 arch/x86/kvm/x86.c              |  8 +++-----
 4 files changed, 3 insertions(+), 23 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 90840593cd6c..e218d907ba46 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1100,7 +1100,6 @@ struct kvm_x86_ops {
 	void (*set_idt)(struct kvm_vcpu *vcpu, struct desc_ptr *dt);
 	void (*get_gdt)(struct kvm_vcpu *vcpu, struct desc_ptr *dt);
 	void (*set_gdt)(struct kvm_vcpu *vcpu, struct desc_ptr *dt);
-	u64 (*get_dr6)(struct kvm_vcpu *vcpu);
 	void (*set_dr6)(struct kvm_vcpu *vcpu, unsigned long value);
 	void (*sync_dirty_debug_regs)(struct kvm_vcpu *vcpu);
 	void (*set_dr7)(struct kvm_vcpu *vcpu, unsigned long value);
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 6b65c75b6816..d8bc1b78a3c6 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1652,11 +1652,6 @@ static void new_asid(struct vcpu_svm *svm, struct svm_cpu_data *sd)
 	mark_dirty(svm->vmcb, VMCB_ASID);
 }
 
-static u64 svm_get_dr6(struct kvm_vcpu *vcpu)
-{
-	return vcpu->arch.dr6;
-}
-
 static void svm_set_dr6(struct kvm_vcpu *vcpu, unsigned long value)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
@@ -3996,7 +3991,6 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {
 	.set_idt = svm_set_idt,
 	.get_gdt = svm_get_gdt,
 	.set_gdt = svm_set_gdt,
-	.get_dr6 = svm_get_dr6,
 	.set_dr6 = svm_set_dr6,
 	.set_dr7 = svm_set_dr7,
 	.sync_dirty_debug_regs = svm_sync_dirty_debug_regs,
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index fce11f2c4c55..82042b7028a9 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -5023,15 +5023,6 @@ static int handle_dr(struct kvm_vcpu *vcpu)
 	return kvm_skip_emulated_instruction(vcpu);
 }
 
-static u64 vmx_get_dr6(struct kvm_vcpu *vcpu)
-{
-	return vcpu->arch.dr6;
-}
-
-static void vmx_set_dr6(struct kvm_vcpu *vcpu, unsigned long val)
-{
-}
-
 static void vmx_sync_dirty_debug_regs(struct kvm_vcpu *vcpu)
 {
 	get_debugreg(vcpu->arch.db[0], 0);
@@ -7812,8 +7803,6 @@ static struct kvm_x86_ops vmx_x86_ops __initdata = {
 	.set_idt = vmx_set_idt,
 	.get_gdt = vmx_get_gdt,
 	.set_gdt = vmx_set_gdt,
-	.get_dr6 = vmx_get_dr6,
-	.set_dr6 = vmx_set_dr6,
 	.set_dr7 = vmx_set_dr7,
 	.sync_dirty_debug_regs = vmx_sync_dirty_debug_regs,
 	.cache_reg = vmx_cache_reg,
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8ec356ac1e6e..0ba83748cd53 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1069,7 +1069,8 @@ static void kvm_update_dr0123(struct kvm_vcpu *vcpu)
 
 static void kvm_update_dr6(struct kvm_vcpu *vcpu)
 {
-	if (!(vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP))
+	if (!(vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP) &&
+	    kvm_x86_ops.set_dr6)
 		kvm_x86_ops.set_dr6(vcpu, vcpu->arch.dr6);
 }
 
@@ -1148,10 +1149,7 @@ int kvm_get_dr(struct kvm_vcpu *vcpu, int dr, unsigned long *val)
 	case 4:
 		/* fall through */
 	case 6:
-		if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP)
-			*val = vcpu->arch.dr6;
-		else
-			*val = kvm_x86_ops.get_dr6(vcpu);
+		*val = vcpu->arch.dr6;
 		break;
 	case 5:
 		/* fall through */
-- 
2.18.2