linux-kernel - Re: [PATCH] s390: Disable ARCH_WANT_OPTIMIZE_HUGETLB

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Message-ID: <20251030163433.1b178a40@thinkpad-T15>
Date: Thu, 30 Oct 2025 16:34:33 +0100
From: Gerald Schaefer <gerald.schaefer@...ux.ibm.com>
To: Heiko Carstens <hca@...ux.ibm.com>
Cc: Luiz Capitulino <luizcap@...hat.com>,
        Alexander Gordeev
 <agordeev@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian
 Borntraeger <borntraeger@...ux.ibm.com>,
        Joao Martins
 <joao.m.martins@...cle.com>,
        David Hildenbrand <david@...hat.com>, osalvador@...e.de,
        aneesh.kumar@...nel.org, akpm@...ux-foundation.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-s390@...r.kernel.org
Subject: Re: [PATCH] s390: Disable ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP

On Thu, 30 Oct 2025 15:55:05 +0100
Heiko Carstens <hca@...ux.ibm.com> wrote:

> As reported by Luiz Capitulino enabling HVO on s390 leads to reproducible
> crashes. The problem is that kernel page tables are modified without
> flushing corresponding TLB entries.
> 
> Even if it looks like the empty flush_tlb_all() implementation on s390 is
> the problem, it is actually a different problem: on s390 it is not allowed
> to replace an active/valid page table entry with another valid page table
> entry without the detour over an invalid entry. A direct replacement may
> lead to random crashes and/or data corruption.
> 
> In order to invalidate an entry special instructions have to be used
> (e.g. ipte or idte). Alternatively there are also special instructions
> available which allow to replace a valid entry with a different valid
> entry (e.g. crdte or cspg).
> 
> Given that the HVO code currently does not provide the hooks to allow for
> an implementation which is compliant with the s390 architecture
> requirements, disable ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP again, which is
> basically a revert of the original patch which enabled it.
> 
> Reported-by: Luiz Capitulino <luizcap@...hat.com>
> Closes: https://lore.kernel.org/all/20251028153930.37107-1-luizcap@redhat.com/
> Fixes: 00a34d5a99c0 ("s390: select ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP")
> Cc: stable@...r.kernel.org
> Signed-off-by: Heiko Carstens <hca@...ux.ibm.com>
> ---
>  arch/s390/Kconfig | 1 -
>  1 file changed, 1 deletion(-)

Thanks!

Reviewed-by: Gerald Schaefer <gerald.schaefer@...ux.ibm.com>