When userspace configures KVM_GUESTDBG_SINGLESTEP, KVM will manage the
presence of X86_EFLAGS_TF via kvm_set/get_rflags on vcpus. The actual
rflag bit is therefore hidden from callers.
That includes init_emulate_ctxt() which uses the value returned from
kvm_get_flags() to set ctxt->tf. As a result, x86_emulate_instruction()
will skip a single step, leaving singlestep_rip stale and not returning
to userspace.
This resolves the issue by observing the vcpu guest_debug configuration
alongside ctxt->tf in x86_emulate_instruction(), performing the single
step if set.
Signed-off-by: Felipe Franciosi <felipe@xxxxxxxxxxx>
---
arch/x86/kvm/x86.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c17e6eb9ad43..78463f01c606 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6919,7 +6919,7 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
if (!ctxt->have_exception ||
exception_type(ctxt->exception.vector) == EXCPT_TRAP) {
kvm_rip_write(vcpu, ctxt->eip);
- if (r && ctxt->tf)
+ if ((r && ctxt->tf) || (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP))
r = kvm_vcpu_do_singlestep(vcpu);
if (kvm_x86_ops.update_emulated_instruction)
kvm_x86_ops.update_emulated_instruction(vcpu);
--
2.20.1
