KVM: SVM: Fix reading of DR6

In contrast to VMX, SVM dose not automatically transfer DR6 into the
VCPU's arch.dr6. So if we face a DR6 read, we must consult a new vendor
hook to obtain the current value. And as SVM now picks the DR6 state
from its VMCB, we also need a set callback in order to write updates of
DR6 back.

Fixes a regression of 020df0794f.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

4 files changed, 45 insertions, 2 deletions

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 33fef0738a29..fdf83afbb7d9 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -700,6 +700,8 @@ 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 (*set_dr7)(struct kvm_vcpu *vcpu, unsigned long value);
         void (*cache_reg)(struct kvm_vcpu *vcpu, enum kvm_reg reg);
         unsigned long (*get_rflags)(struct kvm_vcpu *vcpu);
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index c7168a5cff1b..e81df8fce027 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1671,6 +1671,19 @@ 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 to_svm(vcpu)->vmcb->save.dr6;
+}
+
+static void svm_set_dr6(struct kvm_vcpu *vcpu, unsigned long value)
+{
+        struct vcpu_svm *svm = to_svm(vcpu);
+
+        svm->vmcb->save.dr6 = value;
+        mark_dirty(svm->vmcb, VMCB_DR);
+}
+
 static void svm_set_dr7(struct kvm_vcpu *vcpu, unsigned long value)
 {
         struct vcpu_svm *svm = to_svm(vcpu);
@@ -4286,6 +4299,8 @@ static struct kvm_x86_ops svm_x86_ops = {
         .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,
         .cache_reg = svm_cache_reg,
         .get_rflags = svm_get_rflags,
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 7661eb171936..79b360e4fed1 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -5149,6 +5149,15 @@ static int handle_dr(struct kvm_vcpu *vcpu)
         return 1;
 }
 
+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_set_dr7(struct kvm_vcpu *vcpu, unsigned long val)
 {
         vmcs_writel(GUEST_DR7, val);
@@ -8556,6 +8565,8 @@ static struct kvm_x86_ops vmx_x86_ops = {
         .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,
         .cache_reg = vmx_cache_reg,
         .get_rflags = vmx_get_rflags,
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 59907c9a9d05..59b95b1a04dc 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -722,6 +722,12 @@ unsigned long kvm_get_cr8(struct kvm_vcpu *vcpu)
 }
 EXPORT_SYMBOL_GPL(kvm_get_cr8);
 
+static void kvm_update_dr6(struct kvm_vcpu *vcpu)
+{
+        if (!(vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP))
+                kvm_x86_ops->set_dr6(vcpu, vcpu->arch.dr6);
+}
+
 static void kvm_update_dr7(struct kvm_vcpu *vcpu)
 {
         unsigned long dr7;
@@ -750,6 +756,7 @@ static int __kvm_set_dr(struct kvm_vcpu *vcpu, int dr, unsigned long val)
                 if (val & 0xffffffff00000000ULL)
                         return -1; /* #GP */
                 vcpu->arch.dr6 = (val & DR6_VOLATILE) | DR6_FIXED_1;
+                kvm_update_dr6(vcpu);
                 break;
         case 5:
                 if (kvm_read_cr4_bits(vcpu, X86_CR4_DE))
@@ -791,7 +798,10 @@ static int _kvm_get_dr(struct kvm_vcpu *vcpu, int dr, unsigned long *val)
                         return 1;
                 /* fall through */
         case 6:
-                *val = vcpu->arch.dr6;
+                if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP)
+                        *val = vcpu->arch.dr6;
+                else
+                        *val = kvm_x86_ops->get_dr6(vcpu);
                 break;
         case 5:
                 if (kvm_read_cr4_bits(vcpu, X86_CR4_DE))
@@ -2960,8 +2970,11 @@ static int kvm_vcpu_ioctl_x86_set_vcpu_events(struct kvm_vcpu *vcpu,
 static void kvm_vcpu_ioctl_x86_get_debugregs(struct kvm_vcpu *vcpu,
                                              struct kvm_debugregs *dbgregs)
 {
+        unsigned long val;
+
         memcpy(dbgregs->db, vcpu->arch.db, sizeof(vcpu->arch.db));
-        dbgregs->dr6 = vcpu->arch.dr6;
+        _kvm_get_dr(vcpu, 6, &val);
+        dbgregs->dr6 = val;
         dbgregs->dr7 = vcpu->arch.dr7;
         dbgregs->flags = 0;
         memset(&dbgregs->reserved, 0, sizeof(dbgregs->reserved));
@@ -2975,6 +2988,7 @@ static int kvm_vcpu_ioctl_x86_set_debugregs(struct kvm_vcpu *vcpu,
 
         memcpy(vcpu->arch.db, dbgregs->db, sizeof(vcpu->arch.db));
         vcpu->arch.dr6 = dbgregs->dr6;
+        kvm_update_dr6(vcpu);
         vcpu->arch.dr7 = dbgregs->dr7;
         kvm_update_dr7(vcpu);
 
@@ -6749,6 +6763,7 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu)
 
         memset(vcpu->arch.db, 0, sizeof(vcpu->arch.db));
         vcpu->arch.dr6 = DR6_FIXED_1;
+        kvm_update_dr6(vcpu);
         vcpu->arch.dr7 = DR7_FIXED_1;
         kvm_update_dr7(vcpu);