On Mon, Aug 19, 2019 at 3:01 PM Sean Christopherson <sean.j.christopherson@xxxxxxxxx> wrote: > > On Thu, Aug 15, 2019 at 05:47:12PM -0700, Andy Lutomirski wrote: > > > > > > >> On Jul 29, 2019, at 7:49 PM, Sean Christopherson <sean.j.christopherson@xxxxxxxxx> wrote: > > >> > > >> On Sat, Jul 27, 2019 at 10:38:03AM -0700, Andy Lutomirski wrote: > > >> On Fri, Jul 26, 2019 at 10:52 PM Sean Christopherson > > >> <sean.j.christopherson@xxxxxxxxx> wrote: > > >>> > > >>> Similar to the existing AMD #NPF case where emulation of the current > > >>> instruction is not possible due to lack of information, virtualization > > >>> of Intel SGX will introduce a scenario where emulation is not possible > > >>> due to the VMExit occurring in an SGX enclave. And again similar to > > >>> the AMD case, emulation can be initiated by kvm_mmu_page_fault(), i.e. > > >>> outside of the control of the vendor-specific code. > > >>> > > >>> While the cause and architecturally visible behavior of the two cases > > >>> is different, e.g. Intel SGX will inject a #UD whereas AMD #NPF is a > > >>> clean resume or complete shutdown, the impact on the common emulation > > >>> code is identical: KVM must stop emulation immediately and resume the > > >>> guest. > > >>> > > >>> Replace the exisiting need_emulation_on_page_fault() with a more generic > > >>> is_emulatable() kvm_x86_ops callback, which is called unconditionally > > >>> by x86_emulate_instruction(). > > >> > > >> Having recently noticed that emulate_ud() is broken when the guest's > > >> TF is set, I suppose I should ask: does your new code function > > >> sensibly when TF is set? > > > > > > Barring a VMX fault injection interaction I'm not thinking of, yes. The > > > SGX reaction to the #UD VM-Exit is to inject a #UD and resume the guest, > > > pending breakpoints shouldn't be affected in any way (unless some other > > > part of KVM mucks with them, e.g. when guest single-stepping is enabled). > > > > What I mean is: does the code actually do what you think it does if TF is > > set? Right now, as I understand it, the KVM emulation code has a bug in > > which some emulated faults also inject #DB despite the fact that the > > instruction faulted, and the #DB seems to take precedence over the original > > fault. This confuses the guest. > > Yes. The proposed change is to inject the #UD instead of calling into the > emulator, and by inspection I've verified that all code that injects a #DB > is either contained within the emulator or is mutually exclusive with an > intercepted #UD. It's a qualified yes because I don't have an actual > testcase to verify my literacy. I'll look into adding a test, either to > the selftest/x86/sgx or to kvm-unit-tests. I wrote one, and it fails: # ./tools/testing/selftests/x86/syscall_arg_fault_32 [RUN] SYSENTER with invalid state [OK] Seems okay [RUN] SYSCALL with invalid state [SKIP] Illegal instruction [RUN] SYSENTER with TF and invalid state [OK] Seems okay [RUN] SYSCALL with TF and invalid state [WARN] Got stuck single-stepping -- you probably have a KVM bug emulate_ud() is buggy.
