Re: [Qemu-devel] [PATCH 07/10] target-s390x: enable fully implemented facilities

[Alexander Graf <agraf@suse.de>]

On 25.05.15 23:13, Aurelien Jarno wrote:
> On 2015-05-25 23:04, Alexander Graf wrote:
>>
>>
>> On 25.05.15 23:02, Aurelien Jarno wrote:
>>> On 2015-05-25 22:39, Alexander Graf wrote:
>>>>
>>>>
>>>> On 25.05.15 01:47, Aurelien Jarno wrote:
>>>>> Cc: Alexander Graf <agraf@suse.de>
>>>>> Cc: Richard Henderson <rth@twiddle.net>
>>>>> Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
>>>>
>>>> Shouldn't this get populated based on the selected -cpu type?
>>>
>>> In the long term yes, but given we only implement one CPU type (or
>>> rather none) in TCG mode, we can consider that's already the case.
>>
>> There are patches coming from IBM to at least add a list of a good
>> number of s390x cpu types. I'd really like to make use of that and have
>> actual CPU types selectable.
> 
> I guess they are for the KVM mode. Do they provide the corresponding 
> facilities list? Probably otherwise that doesn't really differentiate
> various CPUs. Please make sure of that when reviewing these patches.

I could definitely use help on review - it's probably my weakest point ;).

>> At least let's move towards that model. So the code in question should
>> take the facility capabilities from the first cpu object (or the class?)
>> for example and we bump it to the currently supported feature set in there.
> 
> Yes, that would work for STFL/STFLE, though we should have a list of
> facilities implemented by TCG so we can mask out the non-implemented
> facilities. This basically corresponds to the informations provided by
> the current patch.

Ah, so you consider the current list the "these are the features TCG
knows about" list?

> That said that won't work for actually disabling the corresponding
> instructions as we don't have a 1 to 1 mapping between the facilities
> and the group of instructions. Anyway we don't even check that right
> now.

I agree, but the TCG code annotates which facility each opcode belongs
to which means actually limiting it should become trivial. That's really
all I'm asking for - I want to see the light at the end of the tunnel ;).


Alex