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SubjectRe: [RFC PATCH 08/21] KVM: x86: Add kvm_x86_ops hook to short circuit emulation
On Fri, Jul 26, 2019 at 10:52 PM Sean Christopherson
<sean.j.christopherson@intel.com> 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?

Also, anyone want to fix that emulate_ud() bug? The test case is merged now:

# ./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

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