On Mon, Sep 17, 2018 at 12:07 PM, Jim Mattson <jmattson@xxxxxxxxxx> wrote:
> When L0 enumerates support for an instruction not supported by the
> physical CPU, it must emulate that instruction for L2 as well as for
> L1. Take MOVBE, for example. If hardware reports that
> CPUID.1:ECX.MOVBE[bit 22] is clear, but L0 sets the bit when emulating
> CPUID for L1, then L0 is obligated to intercept #UD and emulate the
> MOVBE instruction for L1. Furthermore, L0 is also obligated to
> intercept #UD and emulate the MOVBE instruction for L2. Even if L1
> chooses to intercept #UD, L0 must be prepared to decode the
> instruction and emulate MOVBE before deciding to reflect the #UD
> VM-exit to L1.
>
> Rewriting the wrong hypercall instruction with the correct hypercall
> instruction is not as clear-cut. One could argue that this is a
> property of a kvm virtual CPU, and that L0 should always do
> it. However, to avoid surprises, I've preserved the existing behavior
> (right or wrong).
>
> Signed-off-by: Jim Mattson <jmattson@xxxxxxxxxx>
> ---
> arch/x86/kvm/vmx.c | 2 ++
> arch/x86/kvm/x86.c | 6 ++++++
> 2 files changed, 8 insertions(+)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 533a327372c8..c9d8ab3ce56e 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -9649,6 +9649,8 @@ static bool nested_vmx_exit_reflected(struct kvm_vcpu *vcpu, u32 exit_reason)
> else if (is_breakpoint(intr_info) &&
> vcpu->guest_debug & KVM_GUESTDBG_USE_SW_BP)
> return false;
> + else if (is_invalid_opcode(intr_info))
> + return false;
> return vmcs12->exception_bitmap &
> (1u << (intr_info & INTR_INFO_VECTOR_MASK));
> case EXIT_REASON_EXTERNAL_INTERRUPT:
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 542f6315444d..212067531050 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6876,6 +6876,12 @@ static int emulator_fix_hypercall(struct x86_emulate_ctxt *ctxt)
> char instruction[3];
> unsigned long rip = kvm_rip_read(vcpu);
>
> + if (is_guest_mode(vcpu)) {
> + ctxt->exception.vector = UD_VECTOR;
> + ctxt->exception.error_code_valid = false;
> + return X86EMUL_PROPAGATE_FAULT;
> + }
> +
> kvm_x86_ops->patch_hypercall(vcpu, instruction);
>
> return emulator_write_emulated(ctxt, rip, instruction, 3,
> --
> 2.19.0.397.gdd90340f6a-goog
>
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