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Thu, 27 Aug 2026 08:11:58 +0000 (GMT) Received: from osiris (unknown [9.87.85.9]) by smtpav05.fra02v.mail.ibm.com (Postfix) with ESMTPS; Thu, 27 Aug 2026 08:11:57 +0000 (GMT) Date: Thu, 27 Aug 2026 10:11:56 +0200 From: Heiko Carstens To: Alexander Gordeev Cc: Gerald Schaefer , Christian Borntraeger , Vasily Gorbik , Claudio Imbrenda , Andrey Ryabinin , linux-s390@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com Subject: Re: [PATCH v7 2/4] s390/mm: Batch PTE updates in lazy MMU mode Message-ID: <20260827081156.3869103Abc-hca@linux.ibm.com> References: <20260824104048.11040Cdc-hca@linux.ibm.com> <73a0a916-b39f-4ebe-bffe-448928b13bef-agordeev@linux.ibm.com> <20260826130257.21444B1a-hca@linux.ibm.com> <87a3147f-e993-4629-b0dd-a54aefbf20b1-agordeev@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-s390@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: <87a3147f-e993-4629-b0dd-a54aefbf20b1-agordeev@linux.ibm.com> X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-ORIG-GUID: RMz3UEJ-r8qieNoHL4ycj93WaDCZbMla X-Proofpoint-Spam-Info: AW1haW4tMjYwODI3MDA2NSBTYWx0ZWRfXxDOK4nNPsJ0x N8pNfaJzpB9X32TcR8mWrpXp/Px3HuuZuYx1BsQm6Zy8KPzmK6dtck4yDmQygbewzt1gzBQnROc 0IQgPcFHarz21BoDZ01g3zdkD7F6sPk= X-Proofpoint-GUID: jmFqgWxCJxbuJbgYxAqSnoMOcsSUPEsa X-Authority-Analysis: v=2.4 cv=JZyMa0KV c=1 sm=1 tr=0 ts=6a8ff153 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=kj9zAlcOel0A:10 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=tYSU0nxKdXOZT8UyD_gA:9 a=CjuIK1q_8ugA:10 a=zZCYzV9kfG8A:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODI3MDA2NSBTYWx0ZWRfXzOMYH3+JQgpk SERRZa/ETk+hqzm3M4JrFS+PKizommTCwb8ejt4dfPqJ9knc/mfyRBhYVQtGnYz+Q83ta4aeJ68 XefgdioHOI8gqY8HC3xA//2gLsQ18py6CAWYAwMQ7KBsmfDuS2qNt6NhZmDgARLfqN7YlGXgPS8 IXo9YUgXe8QjEpsxJAxaKye32U0Ljn6NeQK3lHmH4kaYhkq03wZUDw/QuGqLxn3UAuoJwEdX7sO UUkO3aHlHKZvm//sNZauHXP96H6yIwQqKoyZiV8zPGTm31RiCLxtzXdO9OpUCtlgA+hIsJMqevQ Dexqa8W5PlrVQjJOZizISywylE3D7PhTIHL4QdkMxbhPehw5DVwANokoAV0IJ7gvbcATviLqv/3 xFwhu8doL4RX7BoGC+nF2BWNwi7URtJvcolHpHf/IFSapfpCzBAHhsqijbOvXmFB949LWPM3FTl O25+Hqzwf/gsZunLkqw== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-08-27_03,2026-08-26_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 clxscore=1015 adultscore=0 priorityscore=1501 impostorscore=0 malwarescore=0 bulkscore=0 lowpriorityscore=0 suspectscore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608270065 On Wed, Aug 26, 2026 at 04:34:25PM +0200, Alexander Gordeev wrote: > On Wed, Aug 26, 2026 at 03:02:57PM +0200, Heiko Carstens wrote: > > Would be nice if we could avoid the not so obvious local_bh_disable() > > and local_bh_enable() pairs. > > Calling ptep_get() from BH context was certainly unexpected, but the way > local_bh_enable|disable() pairs are used is actually straightforward. > This is a slow path anyway, so I would think the simplicity prevails in > this case. > > But again, I will try to avoid that. I do agree that ptep_get() being called from BH context is not what I would have expected too. But then again, nothing prevents people from doing that from irq context too, no matter if that is sane or not. Imho the "final" version should either be implemented that it can go without disabling bottom halves, or, if that is not worth the effort, even disable interrupts, just to avoid other surprises. Plus a comment why it is needed, please.