Re: [PATCH] KVM: s390: vsie: retry SIE instruction on host intercepts

[Christian Borntraeger <borntraeger@linux.ibm.com>]

Am 04.03.24 um 09:35 schrieb David Hildenbrand:
> On 01.03.24 21:43, Eric Farman wrote:
>> It's possible that SIE exits for work that the host needs to perform
>> rather than something that is intended for the guest.
>>
>> A Linux guest will ignore this intercept code since there is nothing
>> for it to do, but a more robust solution would rewind the PSW back to
>> the SIE instruction. This will transparently resume the guest once
>> the host completes its work, without the guest needing to process
>> what is effectively a NOP and re-issue SIE itself.
> 
> I recall that 0-intercepts are valid by the architecture. Further, I recall that there were some rather tricky corner cases where avoiding 0-intercepts would not be that easy.
> 
> Now, it's been a while ago, and maybe I misremember. SoI'm trusting people with access to documentation can review this.

Yes, 0-intercepts are allowed, and this also happens when LPAR has an exit.
So this patch is not necessary, the question is if this would be an valuable optimization?