Re: [PATCH v3] s390/kvm: fix diag318 propagation and reset functionality

[Collin Walling]

On 11/24/20 11:51 AM, Thomas Huth wrote:
> On 24/11/2020 17.26, Collin Walling wrote:
>> On 11/24/20 8:04 AM, Christian Borntraeger wrote:
>>>
>>> On 24.11.20 13:48, Christian Borntraeger wrote:
>>>> Now that we have this - fully implemented in QEMU - shouldnt
>>>> we add els and diag318 also to the default CPU models?
>>>
>>> At least the extended SCCB should be fine to be enabled all the 
>>> time.
>>>
>>
>> Yeah ELS should be fine to default-enable since it's handled entirely
>> via QEMU. If the kernel can support it, great. If not, then the kernel
>> will simply provide the original 4K SCCB.
>>
>> DIAG318 requires KVM support, so I do not think we should default-enable
>> that one :)
> 
> Ok, but does ELS have any advantages as long as you don't use diag318? If we
> do not enable diag318 by default, what sense does it make to enable ELS by
> default?
> 
>  Thomas
> 
> 

One immediate benefit is that it would make configuring a guest to
enable diag318 require one less step. Right now, the VM must explicitly
enable both ELS *and* diag318 in order to use the latter feature. With
ELS default-enabled, the user would only have to explicitly enable
diag318 if they want it.

-- 
Regards,
Collin

Stay safe and stay healthy