[PATCH 2/2] KVM: x86: Preserve guest single-stepping on register

[Jan Kiszka <jan.kiszka@web.de>]

Give user space more flexibility /wrt its IOCTL order. So far updating
the rflags via KVM_SET_REGS ignored potentially set single-step flags.
Now they will be kept.

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

 arch/x86/kvm/x86.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index aa5d574..9fbb4c8 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3853,6 +3853,8 @@ int kvm_arch_vcpu_ioctl_get_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
 
 int kvm_arch_vcpu_ioctl_set_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
 {
+	unsigned long rflags;
+
 	vcpu_load(vcpu);
 
 	kvm_register_write(vcpu, VCPU_REGS_RAX, regs->rax);
@@ -3876,8 +3878,11 @@ int kvm_arch_vcpu_ioctl_set_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
 #endif
 
 	kvm_rip_write(vcpu, regs->rip);
-	kvm_x86_ops->set_rflags(vcpu, regs->rflags);
 
+	rflags = regs->rflags;
+	if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)
+		rflags |= X86_EFLAGS_TF | X86_EFLAGS_RF;
+	kvm_x86_ops->set_rflags(vcpu, rflags);
 
 	vcpu->arch.exception.pending = false;