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[2003:d8:2f3f:4b00:ee13:8c22:5cc5:d169]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-475dd489e6dsm144533855e9.6.2025.10.27.09.59.57 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 27 Oct 2025 09:59:59 -0700 (PDT) Message-ID: Date: Mon, 27 Oct 2025 17:59:57 +0100 Precedence: bulk X-Mailing-List: linux-next@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: Claudio Imbrenda Cc: Christian Borntraeger , Balbir Singh , 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> <74272098-cfb7-424b-a55e-55e94f04524e@linux.ibm.com> <84349344-b127-41f6-99f1-10f907c2bd07@redhat.com> <748cdc18-e32d-41bd-90d1-a102b1c51e06@redhat.com> <20251027174726.5d8fcce7@p-imbrenda> 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 27.10.25 17:47, Claudio Imbrenda wrote: > On Mon, 20 Oct 2025 10:41:28 +0200 > David Hildenbrand wrote: > >> On 20.10.25 09:00, Christian Borntraeger wrote: >>> Am 17.10.25 um 23:56 schrieb Balbir Singh: >>> >>>> In the meanwhile, does this fix/workaround work? >>>> >>>> diff --git a/mm/pgtable-generic.c b/mm/pgtable-generic.c >>>> index 0c847cdf4fd3..31c1754d5bd4 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_non_present_folio_entry(pmdval))) >>>> goto nomap; >>>> if (unlikely(pmd_trans_huge(pmdval))) >>>> goto nomap; >>>> >>> >>> Yes, this seems to work. >> >> Right, but that's not what we will want here. We'll have to adjust s390x >> gmap code (which is getting redesigned either way) to only take the page >> lock. >> >> In the end, we'll want here later a single >> >> if (!pmd_present(pmdval)) >> goto nomap; >> > > this seems to do the trick: > > diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c > index 8ff6bba107e8..22c448b32340 100644 > --- a/arch/s390/mm/gmap.c > +++ b/arch/s390/mm/gmap.c > @@ -599,8 +599,9 @@ int __gmap_link(struct gmap *gmap, unsigned long > gaddr, unsigned long vmaddr) | _SEGMENT_ENTRY_GMAP_UC > | _SEGMENT_ENTRY; > } else > - *table = pmd_val(*pmd) & > - _SEGMENT_ENTRY_HARDWARE_BITS; > + *table = (pmd_val(*pmd) & > + _SEGMENT_ENTRY_HARDWARE_BITS) > + | _SEGMENT_ENTRY; Probably worth adding a comment. I remember we don't reuse this bit as a SW bit in gmap code, right? > } > } else if (*table & _SEGMENT_ENTRY_PROTECT && > !(pmd_val(*pmd) & _SEGMENT_ENTRY_PROTECT)) { > > > > it marks non-leaf gmap segment (pmd) entries as present, just as normal > pmds would be. Yeah, I looked into hand-coding the PTL lookup but it just gets nasty real quick. > > I think it's a good enough fix for now, pending the rewrite, which I > hope to get in the next merge window Agreed. -- Cheers David / dhildenb