KVM: x86: respect singlestep when emulating instruction
commit 384dea1c9183880be183cfaae161d99aafd16df6 upstream. 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. Cc: stable@vger.kernel.org Signed-off-by: Felipe Franciosi <felipe@nutanix.com> Message-Id: <20200519081048.8204-1-felipe@nutanix.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@ -6833,7 +6833,7 @@ restart:
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if (!ctxt->have_exception ||
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exception_type(ctxt->exception.vector) == EXCPT_TRAP) {
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kvm_rip_write(vcpu, ctxt->eip);
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if (r && ctxt->tf)
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if (r && (ctxt->tf || (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)))
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r = kvm_vcpu_do_singlestep(vcpu);
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__kvm_set_rflags(vcpu, ctxt->eflags);
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}
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