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

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Message-ID: <20251020110444.18981271@p-imbrenda>
Date: Mon, 20 Oct 2025 11:04:44 +0200
From: Claudio Imbrenda <imbrenda@...ux.ibm.com>
To: David Hildenbrand <david@...hat.com>
Cc: Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Balbir Singh
 <balbirs@...dia.com>, Liam.Howlett@...cle.com,
        airlied@...il.com, akpm@...ux-foundation.org, apopple@...dia.com,
        baohua@...nel.org, baolin.wang@...ux.alibaba.com, byungchul@...com,
        dakr@...nel.org, dev.jain@....com, dri-devel@...ts.freedesktop.org,
        francois.dugast@...el.com, gourry@...rry.net, joshua.hahnjy@...il.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        lorenzo.stoakes@...cle.com, lyude@...hat.com, matthew.brost@...el.com,
        mpenttil@...hat.com, npache@...hat.com, osalvador@...e.de,
        rakie.kim@...com, rcampbell@...dia.com, ryan.roberts@....com,
        simona@...ll.ch, ying.huang@...ux.alibaba.com, ziy@...dia.com,
        kvm@...r.kernel.org, linux-s390@...r.kernel.org,
        linux-next@...r.kernel.org
Subject: Re: linux-next: KVM/s390x regression

On Mon, 20 Oct 2025 10:41:28 +0200
David Hildenbrand <david@...hat.com> 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 

I'm looking into that

> gmap code (which is getting redesigned either way) to only take the page 

unfortunately the rework won't make it in 6.18, so I'll have to quickly
cobble together a fix

> lock.
> 
> In the end, we'll want here later a single
> 
> if (!pmd_present(pmdval))
> 	goto nomap;
>