Re: [PATCH 1/2] KVM: x86: Add emulation support for #GP triggered by VM instructions

[Paolo Bonzini]

On 15/01/21 08:00, Wei Huang wrote:
> If the whole body inside if-statement is moved out, do you expect the
> interface of x86_emulate_decoded_instruction to be something like:
>
> int x86_emulate_decoded_instruction(struct kvm_vcpu *vcpu,
>                                      gpa_t cr2_or_gpa,
>                                      int emulation_type, void *insn,
>                                      int insn_len,
>                                      bool write_fault_to_spt)

An idea is to making the body of the new function just

        init_emulate_ctxt(vcpu);

        /*
         * We will reenter on the same instruction since
         * we do not set complete_userspace_io.  This does not
         * handle watchpoints yet, those would be handled in
         * the emulate_ops.
         */
        if (!(emulation_type & EMULTYPE_SKIP) &&
            kvm_vcpu_check_breakpoint(vcpu, &r))
                return r;

        ctxt->interruptibility = 0;
        ctxt->have_exception = false;
        ctxt->exception.vector = -1;
        ctxt->exception.error_code_valid = false;

        ctxt->perm_ok = false;

        ctxt->ud = emulation_type & EMULTYPE_TRAP_UD;

        r = x86_decode_insn(ctxt, insn, insn_len);

        trace_kvm_emulate_insn_start(vcpu);
        ++vcpu->stat.insn_emulation;
        return r;

because for the new caller, on EMULATION_FAILED you can just re-enter 
the guest.

> And if so, what is the emulation type to use when calling this function
> from svm.c? EMULTYPE_VMWARE_GP?

Just 0 I think.

Paolo