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Wed, 29 Oct 2025 12:49:54 +0000 (GMT) Date: Wed, 29 Oct 2025 13:49:53 +0100 From: Heiko Carstens To: David Hildenbrand Cc: Luiz Capitulino , borntraeger@linux.ibm.com, joao.m.martins@oracle.com, mike.kravetz@oracle.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-s390@vger.kernel.org, gor@linux.ibm.com, gerald.schaefer@linux.ibm.com, agordeev@linux.ibm.com, osalvador@suse.de, akpm@linux-foundation.org, aneesh.kumar@kernel.org Subject: Re: [PATCH v2] s390: fix HugeTLB vmemmap optimization crash Message-ID: <20251029124953.8393Cc7-hca@linux.ibm.com> References: <20251028211533.47694-1-luizcap@redhat.com> <6bbdf4ce-10e3-429b-89fc-ef000f118fec@redhat.com> <20251029104457.8393B96-hca@linux.ibm.com> <9a8254b9-92f8-4530-88e8-fca3b7465908@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9a8254b9-92f8-4530-88e8-fca3b7465908@redhat.com> X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=ALkgKXG8 c=1 sm=1 tr=0 ts=69020d77 cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=kj9zAlcOel0A:10 a=x6icFKpwvdMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=jL9k_VB0GEcHRAsgpWwA:9 a=CjuIK1q_8ugA:10 a=cPQSjfK2_nFv0Q5t_7PE:22 X-Proofpoint-ORIG-GUID: d7fou95aMW-uoHoBvQs44vXWPA3v3hlP X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMDI4MDE2NiBTYWx0ZWRfX/oTo6Xh50MtI tyftiHDyPqefL6i4ewtPwSFaHIfzYG5hcU61cVUCmE90icNKNJPTPq2CeETrBXDHeI0rfosiAQy K6ZTRo5A7we91nVh7IppPMSZN8yrpEPNjTjmrsrK28U9Xgz4MO2dRmcScvGoQx0iHbFV8ABTarp odLOX8K8D+KdOEOSAlIm2XNTojsSqNjGYdiCQOX7+GmbYtyHz0AnRA4jiGZ5u5KBbpTBWKEcgVn Zn7Bkm78kGwYsfxNvb/77vQlYtBAgylrI//8hvqa916XjUWCSw7QwYAw+cdvxUvYX+CI5G9jgnv OK2GtuYXvZhVIT81bggT50K+vpwF85EZ8LUrZ/Dx8caprN82Fr8OnUromFPNKBb27BB6p37t/TC N3kUgCnqtPVrQ5t7cUHB4gB/Jke0Iw== X-Proofpoint-GUID: d7fou95aMW-uoHoBvQs44vXWPA3v3hlP X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2025-10-29_05,2025-10-29_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 suspectscore=0 impostorscore=0 lowpriorityscore=0 clxscore=1015 adultscore=0 bulkscore=0 malwarescore=0 phishscore=0 spamscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2510240000 definitions=main-2510280166 On Wed, Oct 29, 2025 at 01:15:44PM +0100, David Hildenbrand wrote: > BTW, I'm staring at s390x's flush_tlb() function and wonder why that one is > defined. I'm sure there is a good reason ;) Yes, I stumbled across that yesterday evening as well. I think its only purpose is that it wants to be deleted :). I just didn't do it yet since I don't want to see a merge conflict with this patch. I also need to check if the only usage of flush_tlb_page(), which is also a no-op for s390, in mm/memory.c is not indicating a problem too. > > Changing active entries without the detour over an invalid entry or using > > proper instructions like crdte or cspg is not allowed on s390. This was solved > > for other parts that change active entries of the kernel mapping in an > > architecture compliant way for s390 (see arch/s390/mm/pageattr.c). > > Good point. I recall ARM64 has similar break-before-make requirements > because they cannot tolerate two different TLB entries (small vs. large) for > the same virtual address. > > And if I rememebr correctly, that's the reason why arm64 does not enable > ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP just yet. Ok, let's wait for Gerald. Maybe there is a non-obvious reason why this works anyway.