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Sun, 02 Nov 2025 21:24:04 -0800 (PST) Received: from dw-tp ([171.76.85.117]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-7a7db86f0fesm9646002b3a.60.2025.11.02.21.24.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 02 Nov 2025 21:24:04 -0800 (PST) From: Ritesh Harjani (IBM) To: Heiko Carstens , Luiz Capitulino , Gerald Schaefer , Alexander Gordeev , Vasily Gorbik , Christian Borntraeger Cc: Joao Martins , David Hildenbrand , osalvador@suse.de, aneesh.kumar@kernel.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-s390@vger.kernel.org Subject: Re: [PATCH] s390: Disable ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP In-Reply-To: <20251030145505.2764038-1-hca@linux.ibm.com> Date: Mon, 03 Nov 2025 10:29:29 +0530 Message-ID: <87zf934spa.ritesh.list@gmail.com> References: <20251030145505.2764038-1-hca@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Heiko Carstens writes: > 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 > Closes: https://lore.kernel.org/all/20251028153930.37107-1-luizcap@redhat.com/ > Fixes: 00a34d5a99c0 ("s390: select ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP") > Cc: stable@vger.kernel.org > Signed-off-by: Heiko Carstens > --- > arch/s390/Kconfig | 1 - > 1 file changed, 1 deletion(-) Yup architectures like aarch64 and PPC64 keep it disable for the same reason. However patch [1] allows for enabling similar optimization for DAX vmemmap "ARCH_WANT_OPTIMIZE_DAX_VMEMMAP", if DAX is supported. I see in 6.18-1 pull request s390 had "Add DAX support for DCSS memory block devices". [1]: https://lore.kernel.org/all/20230724190759.483013-8-aneesh.kumar@linux.ibm.com/T/#u -ritesh > > diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig > index c4145672ca34..df22b10d9141 100644 > --- a/arch/s390/Kconfig > +++ b/arch/s390/Kconfig > @@ -158,7 +158,6 @@ config S390 > select ARCH_WANT_IRQS_OFF_ACTIVATE_MM > select ARCH_WANT_KERNEL_PMD_MKWRITE > select ARCH_WANT_LD_ORPHAN_WARN > - select ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP > select ARCH_WANTS_THP_SWAP > select BUILDTIME_TABLE_SORT > select CLONE_BACKWARDS2 > -- > 2.48.1