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[2003:d8:2f0c:c200:fa4a:c4ff:1b32:21ce]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-47114428dbfsm85439735e9.5.2025.10.17.08.07.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 17 Oct 2025 08:07:54 -0700 (PDT) Message-ID: <8c778cd0-5608-4852-9840-4d98828d7b33@redhat.com> Date: Fri, 17 Oct 2025 17:07:53 +0200 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: linux-next: KVM/s390x regression To: Christian Borntraeger , balbirs@nvidia.com Cc: Liam.Howlett@oracle.com, airlied@gmail.com, akpm@linux-foundation.org, apopple@nvidia.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, byungchul@sk.com, dakr@kernel.org, dev.jain@arm.com, dri-devel@lists.freedesktop.org, francois.dugast@intel.com, gourry@gourry.net, joshua.hahnjy@gmail.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, lorenzo.stoakes@oracle.com, lyude@redhat.com, matthew.brost@intel.com, mpenttil@redhat.com, npache@redhat.com, osalvador@suse.de, rakie.kim@sk.com, rcampbell@nvidia.com, ryan.roberts@arm.com, simona@ffwll.ch, ying.huang@linux.alibaba.com, ziy@nvidia.com, kvm@vger.kernel.org, linux-s390@vger.kernel.org, linux-next@vger.kernel.org References: <20251001065707.920170-4-balbirs@nvidia.com> <20251017144924.10034-1-borntraeger@linux.ibm.com> <9beff9d6-47c7-4a65-b320-43efd1e12687@redhat.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 17.10.25 17:01, Christian Borntraeger wrote: > 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? Not sure ... it's a bit weird. I mean, when KVM disables THPs we essentially just remap everything to be mapped by PTEs. So there shouldn't be any PMDs in that whole process. Remapping a file THP (shmem) implies zapping the THP completely. I assume in your kernel config has CONFIG_ZONE_DEVICE and CONFIG_ARCH_ENABLE_THP_MIGRATION set, right? I'd rule out copy_huge_pmd(), zap_huge_pmd() a well. What happens if you revert the change in mm/pgtable-generic.c? But the whole -ENOMEM error is a weird symptom. -- Cheers David / dhildenb