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>

1 files changed, 17 insertions, 9 deletions

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;