>> 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.
