On 19/05/20 10:11, Felipe Franciosi wrote:

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@nutanix.com

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..64cb183636da 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);
  
  

Queued, thanks.

Paolo