KVM: x86: Fix guest debug across vcpu INIT reset

If we reset a vcpu on INIT, we so far overwrote dr7 as provided by
KVM_SET_GUEST_DEBUG, and we also cleared switch_db_regs unconditionally.

Fix this by saving the dr7 used for guest debugging and calculating the
effective register value as well as switch_db_regs on any potential
change. This will change to focus of the set_guest_debug vendor op to
update_dp_bp_intercept.

Found while trying to stop on start_secondary.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

3 files changed, 22 insertions, 41 deletions

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 818fceb3091e..d017df3899ef 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1146,7 +1146,6 @@ static void init_vmcb(struct vcpu_svm *svm)
 
         svm_set_efer(&svm->vcpu, 0);
         save->dr6 = 0xffff0ff0;
-        save->dr7 = 0x400;
         kvm_set_rflags(&svm->vcpu, 2);
         save->rip = 0x0000fff0;
         svm->vcpu.arch.regs[VCPU_REGS_RIP] = save->rip;
@@ -1643,7 +1642,7 @@ static void svm_set_segment(struct kvm_vcpu *vcpu,
         mark_dirty(svm->vmcb, VMCB_SEG);
 }
 
-static void update_db_intercept(struct kvm_vcpu *vcpu)
+static void update_db_bp_intercept(struct kvm_vcpu *vcpu)
 {
         struct vcpu_svm *svm = to_svm(vcpu);
 
@@ -1663,20 +1662,6 @@ static void update_db_intercept(struct kvm_vcpu *vcpu)
                 vcpu->guest_debug = 0;
 }
 
-static void svm_guest_debug(struct kvm_vcpu *vcpu, struct kvm_guest_debug *dbg)
-{
-        struct vcpu_svm *svm = to_svm(vcpu);
-
-        if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP)
-                svm->vmcb->save.dr7 = dbg->arch.debugreg[7];
-        else
-                svm->vmcb->save.dr7 = vcpu->arch.dr7;
-
-        mark_dirty(svm->vmcb, VMCB_DR);
-
-        update_db_intercept(vcpu);
-}
-
 static void new_asid(struct vcpu_svm *svm, struct svm_cpu_data *sd)
 {
         if (sd->next_asid > sd->max_asid) {
@@ -1748,7 +1733,7 @@ static int db_interception(struct vcpu_svm *svm)
                 if (!(svm->vcpu.guest_debug & KVM_GUESTDBG_SINGLESTEP))
                         svm->vmcb->save.rflags &=
                                 ~(X86_EFLAGS_TF | X86_EFLAGS_RF);
-                update_db_intercept(&svm->vcpu);
+                update_db_bp_intercept(&svm->vcpu);
         }
 
         if (svm->vcpu.guest_debug &
@@ -3659,7 +3644,7 @@ static void enable_nmi_window(struct kvm_vcpu *vcpu)
          */
         svm->nmi_singlestep = true;
         svm->vmcb->save.rflags |= (X86_EFLAGS_TF | X86_EFLAGS_RF);
-        update_db_intercept(vcpu);
+        update_db_bp_intercept(vcpu);
 }
 
 static int svm_set_tss_addr(struct kvm *kvm, unsigned int addr)
@@ -4253,7 +4238,7 @@ static struct kvm_x86_ops svm_x86_ops = {
         .vcpu_load = svm_vcpu_load,
         .vcpu_put = svm_vcpu_put,
 
-        .set_guest_debug = svm_guest_debug,
+        .update_db_bp_intercept = update_db_bp_intercept,
         .get_msr = svm_get_msr,
         .set_msr = svm_set_msr,
         .get_segment_base = svm_get_segment_base,
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 30bcb953afee..5d46c905e06f 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2288,16 +2288,6 @@ static void vmx_cache_reg(struct kvm_vcpu *vcpu, enum kvm_reg reg)
         }
 }
 
-static void set_guest_debug(struct kvm_vcpu *vcpu, struct kvm_guest_debug *dbg)
-{
-        if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP)
-                vmcs_writel(GUEST_DR7, dbg->arch.debugreg[7]);
-        else
-                vmcs_writel(GUEST_DR7, vcpu->arch.dr7);
-
-        update_exception_bitmap(vcpu);
-}
-
 static __init int cpu_has_kvm_support(void)
 {
         return cpu_has_vmx();
@@ -3960,8 +3950,6 @@ static int vmx_vcpu_reset(struct kvm_vcpu *vcpu)
                 kvm_rip_write(vcpu, 0);
         kvm_register_write(vcpu, VCPU_REGS_RSP, 0);
 
-        vmcs_writel(GUEST_DR7, 0x400);
-
         vmcs_writel(GUEST_GDTR_BASE, 0);
         vmcs_write32(GUEST_GDTR_LIMIT, 0xffff);
 
@@ -7237,7 +7225,7 @@ static struct kvm_x86_ops vmx_x86_ops = {
         .vcpu_load = vmx_vcpu_load,
         .vcpu_put = vmx_vcpu_put,
 
-        .set_guest_debug = set_guest_debug,
+        .update_db_bp_intercept = update_exception_bitmap,
         .get_msr = vmx_get_msr,
         .set_msr = vmx_set_msr,
         .get_segment_base = vmx_get_segment_base,
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 7d44204c6041..b16d4a5bfa41 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -692,6 +692,18 @@ unsigned long kvm_get_cr8(struct kvm_vcpu *vcpu)
 }
 EXPORT_SYMBOL_GPL(kvm_get_cr8);
 
+static void kvm_update_dr7(struct kvm_vcpu *vcpu)
+{
+        unsigned long dr7;
+
+        if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP)
+                dr7 = vcpu->arch.guest_debug_dr7;
+        else
+                dr7 = vcpu->arch.dr7;
+        kvm_x86_ops->set_dr7(vcpu, dr7);
+        vcpu->arch.switch_db_regs = (dr7 & DR7_BP_EN_MASK);
+}
+
 static int __kvm_set_dr(struct kvm_vcpu *vcpu, int dr, unsigned long val)
 {
         switch (dr) {
@@ -717,10 +729,7 @@ static int __kvm_set_dr(struct kvm_vcpu *vcpu, int dr, unsigned long val)
                 if (val & 0xffffffff00000000ULL)
                         return -1; /* #GP */
                 vcpu->arch.dr7 = (val & DR7_VOLATILE) | DR7_FIXED_1;
-                if (!(vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP)) {
-                        kvm_x86_ops->set_dr7(vcpu, vcpu->arch.dr7);
-                        vcpu->arch.switch_db_regs = (val & DR7_BP_EN_MASK);
-                }
+                kvm_update_dr7(vcpu);
                 break;
         }
 
@@ -5851,13 +5860,12 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
         if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP) {
                 for (i = 0; i < KVM_NR_DB_REGS; ++i)
                         vcpu->arch.eff_db[i] = dbg->arch.debugreg[i];
-                vcpu->arch.switch_db_regs =
-                        (dbg->arch.debugreg[7] & DR7_BP_EN_MASK);
+                vcpu->arch.guest_debug_dr7 = dbg->arch.debugreg[7];
         } else {
                 for (i = 0; i < KVM_NR_DB_REGS; i++)
                         vcpu->arch.eff_db[i] = vcpu->arch.db[i];
-                vcpu->arch.switch_db_regs = (vcpu->arch.dr7 & DR7_BP_EN_MASK);
         }
+        kvm_update_dr7(vcpu);
 
         if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)
                 vcpu->arch.singlestep_rip = kvm_rip_read(vcpu) +
@@ -5869,7 +5877,7 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
          */
         kvm_set_rflags(vcpu, rflags);
 
-        kvm_x86_ops->set_guest_debug(vcpu, dbg);
+        kvm_x86_ops->update_db_bp_intercept(vcpu);
 
         r = 0;
 
@@ -6045,10 +6053,10 @@ int kvm_arch_vcpu_reset(struct kvm_vcpu *vcpu)
         vcpu->arch.nmi_pending = 0;
         vcpu->arch.nmi_injected = false;
 
-        vcpu->arch.switch_db_regs = 0;
         memset(vcpu->arch.db, 0, sizeof(vcpu->arch.db));
         vcpu->arch.dr6 = DR6_FIXED_1;
         vcpu->arch.dr7 = DR7_FIXED_1;
+        kvm_update_dr7(vcpu);
 
         kvm_make_request(KVM_REQ_EVENT, vcpu);
         vcpu->arch.apf.msr_val = 0;