Re: [Xen-devel] [PATCH for-4.5 2/2] x86/hvm: Improve "Emulation failed @" error messages

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 26/09/14 13:41, Tim Deegan wrote:
> At 13:09 +0100 on 26 Sep (1411733364), Andrew Cooper wrote:
>> On 26/09/14 13:05, Tim Deegan wrote:
>>> At 11:10 +0100 on 26 Sep (1411726207), Andrew Cooper wrote:
>>>> +static const char *guest_x86_mode_to_str(int mode)
>>>> +{
>>>> +    switch ( mode )
>>>> +    {
>>>> +    case 0:
>>>> +        return "Real";
>>>> +    case 1:
>>>> +        return "v8086";
>>>> +    case 2:
>>> return "16bit"?  
>>>
>>> Otherwise, Reviewed-by: Tim Deegan <tim@xxxxxxx>
>>>
>>> While you're respinning, could you also shorten all of these strings
>>> (e.g. to real/vm86/16b/32b/64b), and trim the rest of the line,
>>> something like:
>>>
>>> (d1) MMIO emulation failed: d1v0 64b @ 0008:ffff82d080102fea: 48 63 8d 40 
>>> ff ff ff
>>>
>>> You can keep the reviewed-by regardless of whatever cosmetic changes.
>>>
>>> Cheers,
>>>
>>> Tim.
>> As identified in the other thread, "16bit" is misleading as the
>> instruction bytes are actually 32bit code in a 16bit segment.
>>
>> I am not sure what the best solution here is.  Perhaps we can trust
>> anyone capable of interpreting this error to know that "16b" != "Real"
>> or "v86" when it comes to decoding the instruction.
> Hmm.  I can see that 16bit is a bit misleading if you don't
> know/remember that vm86 and real mode would be reported as such.  OTOH
> that is infomration that's needed for decoding -- the instruction will
> have 16bit operands and addresses even though it uses 32bit registers
> and protected segments.
>
> Maybe we should report it as '16bit protected' or similar?

How about following the convention at http://sandpile.org/x86/mode.htm ?

Currently, we can distinguish between RM16, VM16, (P/C)M{16,32} and
PM64, which is good enough for decoding the bytes correctly.

Alternatively, we could extend {vmx,svm}_guest_x86_mode() to provide a
rather more complete enum of processor modes and cover the other cases?

~Andrew

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