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Fri, 17 Oct 2025 15:20:57 GMT Received: from smtpav07.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id EA2012004B; Fri, 17 Oct 2025 15:20:56 +0000 (GMT) Received: from smtpav07.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id B922020040; Fri, 17 Oct 2025 15:20:55 +0000 (GMT) Received: from [9.111.36.47] (unknown [9.111.36.47]) by smtpav07.fra02v.mail.ibm.com (Postfix) with ESMTP; Fri, 17 Oct 2025 15:20:55 +0000 (GMT) Message-ID: <74272098-cfb7-424b-a55e-55e94f04524e@linux.ibm.com> Date: Fri, 17 Oct 2025 17:20:55 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: linux-next: KVM/s390x regression To: David Hildenbrand , 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> <8c778cd0-5608-4852-9840-4d98828d7b33@redhat.com> Content-Language: en-US From: Christian Borntraeger In-Reply-To: <8c778cd0-5608-4852-9840-4d98828d7b33@redhat.com> Content-Type: text/plain; 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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? yes. > > I'd rule out copy_huge_pmd(), zap_huge_pmd() a well. > > > What happens if you revert the change in mm/pgtable-generic.c? That partial revert seems to fix the issue diff --git a/mm/pgtable-generic.c b/mm/pgtable-generic.c index 0c847cdf4fd3..567e2d084071 100644 --- a/mm/pgtable-generic.c +++ b/mm/pgtable-generic.c @@ -290,7 +290,7 @@ pte_t *___pte_offset_map(pmd_t *pmd, unsigned long addr, pmd_t *pmdvalp) if (pmdvalp) *pmdvalp = pmdval; - if (unlikely(pmd_none(pmdval) || !pmd_present(pmdval))) + if (unlikely(pmd_none(pmdval) || is_pmd_migration_entry(pmdval))) goto nomap; if (unlikely(pmd_trans_huge(pmdval))) goto nomap;