[PATCH] KVM: x86: Fix guest debug across vcpu INIT reset

[Jan Kiszka <jan.kiszka@siemens.com>]

If we reset a vcpu on INIT, make sure to not touch dr7 as stored in the
VMCS/VMCB and also switch_db_regs if guest debugging is using hardware
breakpoints. Otherwise, the vcpu will not trigger hardware breakpoints
until userspace issues another KVM_SET_GUEST_DEBUG IOCTL for it.

Found while trying to stop on start_secondary.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---

Nice to have for stable as well.

 arch/x86/kvm/svm.c |    3 ++-
 arch/x86/kvm/vmx.c |    3 ++-
 arch/x86/kvm/x86.c |    3 ++-
 3 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 611c728..4163ce2 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1146,7 +1146,8 @@ static void init_vmcb(struct vcpu_svm *svm)
 
 	svm_set_efer(&svm->vcpu, 0);
 	save->dr6 = 0xffff0ff0;
-	save->dr7 = 0x400;
+	if (!(svm->vcpu.guest_debug & KVM_GUESTDBG_USE_HW_BP))
+		save->dr7 = 0x400;
 	kvm_set_rflags(&svm->vcpu, 2);
 	save->rip = 0x0000fff0;
 	svm->vcpu.arch.regs[VCPU_REGS_RIP] = save->rip;
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index d62b413..37f68f7 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3959,7 +3959,8 @@ 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);
+	if (!(vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP))
+		vmcs_writel(GUEST_DR7, 0x400);
 
 	vmcs_writel(GUEST_GDTR_BASE, 0);
 	vmcs_write32(GUEST_GDTR_LIMIT, 0xffff);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c4d451e..7c8c2b8 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6043,7 +6043,8 @@ 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;
+	if (!(vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP))
+		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;
-- 
1.7.3.4