| Message ID | 20200519081048.8204-1-felipe@nutanix.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] KVM: x86: respect singlestep when emulating instruction | expand |
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
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);
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(-)