[PATCH 03/10] KVM: x86: Make kvm_x86_ops' {g,s}et_dr6() hooks optional

[Sean Christopherson]

Make get_dr6() and set_dr6() optional and drop the VMX implementations,
which are for all intents and purposes nops.  This avoids a retpoline on
VMX when reading/writing DR6, at minimal cost (~1 uop) to SVM.

Signed-off-by: Sean Christopherson <sean.j.christopher...@intel.com>
---
 arch/x86/kvm/vmx/vmx.c | 11 -----------
 arch/x86/kvm/x86.c     |  6 ++++--
 2 files changed, 4 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index de18cd386bb1..e157bdc218ea 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -5008,15 +5008,6 @@ 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);
@@ -7799,8 +7790,6 @@ 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..eccbfcb6a4e5 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);
 }
 
@@ -1148,7 +1149,8 @@ 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)
+               if ((vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP) ||
+                   !kvm_x86_ops.get_dr6)
                        *val = vcpu->arch.dr6;
                else
                        *val = kvm_x86_ops.get_dr6(vcpu);
-- 
2.26.0