Re: [PATCH RFC V7 1/5] xen: Emulate with no writes

[Razvan Cojocaru <rcojocaru@bitdefender.com>]

On 08/26/2014 04:56 PM, Jan Beulich wrote:
>>>> On 13.08.14 at 17:28, <rcojocaru@bitdefender.com> wrote:
>> +void hvm_emulate_one_full(bool_t nowrite, unsigned int trapnr,
>> +    unsigned int errcode)
>> +{
>> +    struct hvm_emulate_ctxt ctx = {{ 0 }};
>> +    int rc;
>> +
>> +    hvm_emulate_prepare(&ctx, guest_cpu_user_regs());
>> +
>> +    if ( nowrite )
>> +        rc = hvm_emulate_one_no_write(&ctx);
>> +    else
>> +        rc = hvm_emulate_one(&ctx);
>> +
>> +    switch ( rc )
>> +    {
>> +    case X86EMUL_UNHANDLEABLE:
>> +        gdprintk(XENLOG_DEBUG, "Emulation failed @ %04x:%lx: "
>> +               "%02x %02x %02x %02x %02x %02x %02x %02x %02x %02x\n",
>> +               hvmemul_get_seg_reg(x86_seg_cs, &ctx)->sel,
>> +               ctx.insn_buf_eip,
>> +               ctx.insn_buf[0], ctx.insn_buf[1],
>> +               ctx.insn_buf[2], ctx.insn_buf[3],
>> +               ctx.insn_buf[4], ctx.insn_buf[5],
>> +               ctx.insn_buf[6], ctx.insn_buf[7],
>> +               ctx.insn_buf[8], ctx.insn_buf[9]);
>> +        hvm_inject_hw_exception(trapnr, errcode);
>> +        break;
>> +    case X86EMUL_EXCEPTION:
>> +        if ( ctx.exn_pending )
>> +            hvm_inject_hw_exception(ctx.exn_vector, ctx.exn_error_code);
>> +        break;
> 
> Shouldn't you act on X86EMUL_RETRY here? Or at least not fall through
> to the writeback below?

Thanks for the review, I did initially loop around hvm_emulate_one()
until rc != X86EMUL_RETRY, but I've been told that that might block
against time calibration rendezvous points.

I'll avoid the fallthrough in the next version of the series.


Thanks,
Razvan Cojocaru