Subject: Re: linux-next: KVM/s390x regression

From: Christian Borntraeger <[email-masked]>
Date: Fri, 17 Oct 2025 17:01:39 +0200

Am 17.10.25 um 16:54 schrieb David Hildenbrand:
> On 17.10.25 16:49, Christian Borntraeger wrote:
>> This patch triggers a regression for s390x kvm as qemu guests can no longer start
>>
>> error: kvm run failed Cannot allocate memory
>> PSW=mask 0000000180000000 addr 000000007fd00600
>> R00=0000000000000000 R01=0000000000000000 R02=0000000000000000 R03=0000000000000000
>> R04=0000000000000000 R05=0000000000000000 R06=0000000000000000 R07=0000000000000000
>> R08=0000000000000000 R09=0000000000000000 R10=0000000000000000 R11=0000000000000000
>> R12=0000000000000000 R13=0000000000000000 R14=0000000000000000 R15=0000000000000000
>> C00=00000000000000e0 C01=0000000000000000 C02=0000000000000000 C03=0000000000000000
>> C04=0000000000000000 C05=0000000000000000 C06=0000000000000000 C07=0000000000000000
>> C08=0000000000000000 C09=0000000000000000 C10=0000000000000000 C11=0000000000000000
>> C12=0000000000000000 C13=0000000000000000 C14=00000000c2000000 C15=0000000000000000
>>
>> KVM on s390x does not use THP so far, will investigate. Does anyone have a quick idea?
> 
> Only when running KVM guests and apart from that everything else seems to be fine?

We have other weirdness in linux-next but in different areas. Could that somehow be
related to use disabling THP for the kvm address space?