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SubjectRe: [PATCH v5 2/2] KVM: X86: Add Force Emulation Prefix for "emulate the next instruction"
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> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 1eb495e..a55ecef 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -146,6 +146,9 @@ bool __read_mostly enable_vmware_backdoor = false;
> module_param(enable_vmware_backdoor, bool, S_IRUGO);
> EXPORT_SYMBOL_GPL(enable_vmware_backdoor);
>
> +static bool __read_mostly force_emulation_prefix = false;
> +module_param(force_emulation_prefix, bool, S_IRUGO);
> +
> #define KVM_NR_SHARED_MSRS 16
>
> struct kvm_shared_msrs_global {
> @@ -4844,6 +4847,21 @@ int handle_ud(struct kvm_vcpu *vcpu)
> {
> enum emulation_result er;
>
> + if (force_emulation_prefix) {
> + char sig[5]; /* ud2; .ascii "kvm" */
> + struct x86_exception e;
> +
> + if (kvm_read_guest_virt(&vcpu->arch.emulate_ctxt,
> + kvm_get_linear_rip(vcpu), sig, sizeof(sig), &e))
> + goto emulate_ud;
> +
> + if (memcmp(sig, "\xf\xbkvm", sizeof(sig)) == 0) {
> + kvm_rip_write(vcpu, kvm_rip_read(vcpu) + sizeof(sig));
> + return emulate_instruction(vcpu, 0) == EMULATE_DONE;

What if we would have an invalid instruction here? Shouldn't you handle
the emulate_instruction() like below?
(e.g. keep a variable with the emulation type (0 vs EMULTYPE_TRAP_UD)
and reuse emulate_ud below)

> + }
> + }
> +
> +emulate_ud:
> er = emulate_instruction(vcpu, EMULTYPE_TRAP_UD);
> if (er == EMULATE_USER_EXIT)
> return 0;
>


--

Thanks,

David / dhildenb

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