linux-kernel - Re: [PATCH v2] s390: fix HugeTLB vmemmap optimization crash

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Message-Id: <20251028145334.5a97211e0e46ca42fe2fa0d0@linux-foundation.org>
Date: Tue, 28 Oct 2025 14:53:34 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Luiz Capitulino <luizcap@...hat.com>
Cc: hca@...ux.ibm.com, borntraeger@...ux.ibm.com, joao.m.martins@...cle.com,
 mike.kravetz@...cle.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 linux-s390@...r.kernel.org, gor@...ux.ibm.com,
 gerald.schaefer@...ux.ibm.com, agordeev@...ux.ibm.com, osalvador@...e.de,
 david@...hat.com, aneesh.kumar@...nel.org
Subject: Re: [PATCH v2] s390: fix HugeTLB vmemmap optimization crash

On Tue, 28 Oct 2025 17:15:33 -0400 Luiz Capitulino <luizcap@...hat.com> wrote:

> A reproducible crash occurs when enabling HugeTLB vmemmap optimization (HVO)
> on s390. The crash and the proposed fix were worked on an s390 KVM guest
> running on an older hypervisor, as I don't have access to an LPAR. However,
> the same issue should occur on bare-metal.
> 
> Reproducer (it may take a few runs to trigger):
> 
>  # sysctl vm.hugetlb_optimize_vmemmap=1
>  # echo 1 > /proc/sys/vm/nr_hugepages
>  # echo 0 > /proc/sys/vm/nr_hugepages
> 
> ...
> 
> This commit fixes this by implementing flush_tlb_all() on s390 as an
> alias to __tlb_flush_global(). This should cause a flush on all TLB
> entries on all CPUs as expected by the flush_tlb_all() semantics.
> 
> ...
>
>  arch/s390/include/asm/tlbflush.h | 6 +++++-

Thanks, I'll add this to mm.git.  If s390 people prefer to merge it
(or nack it!) then please do so and I'll drop the mm.git copy.