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Fri, 5 Sep 2025 09:46:26 GMT Received: from smtpav04.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id BCE5220040; Fri, 5 Sep 2025 09:46:26 +0000 (GMT) Received: from smtpav04.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id AF00220063; Fri, 5 Sep 2025 09:46:24 +0000 (GMT) Received: from li-008a6a4c-3549-11b2-a85c-c5cc2836eea2.ibm.com (unknown [9.111.88.103]) by smtpav04.fra02v.mail.ibm.com (Postfix) with ESMTPS; Fri, 5 Sep 2025 09:46:24 +0000 (GMT) Date: Fri, 5 Sep 2025 11:46:23 +0200 From: Alexander Gordeev To: Kevin Brodsky Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andreas Larsson , Andrew Morton , Boris Ostrovsky , Borislav Petkov , Catalin Marinas , Christophe Leroy , Dave Hansen , David Hildenbrand , "David S. Miller" , "H. Peter Anvin" , Ingo Molnar , Jann Horn , Juergen Gross , "Liam R. Howlett" , Lorenzo Stoakes , Madhavan Srinivasan , Michael Ellerman , Michal Hocko , Mike Rapoport , Nicholas Piggin , Peter Zijlstra , Ryan Roberts , Suren Baghdasaryan , Thomas Gleixner , Vlastimil Babka , Will Deacon , linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, sparclinux@vger.kernel.org, xen-devel@lists.xenproject.org Subject: Re: [PATCH 0/7] Nesting support for lazy MMU mode Message-ID: <9fd076c7-f163-4b92-8201-d8a259a338c1-agordeev@linux.ibm.com> References: <20250904125736.3918646-1-kevin.brodsky@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250904125736.3918646-1-kevin.brodsky@arm.com> X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwODMwMDAzMCBTYWx0ZWRfX0b7vKa9wIqUd 15JIKVxY/eFyoNy0/rx0rVDv/Yc4PB6ogniG6U5JZlC8qyn8Y0NgFv6oYYbeCaWjZF7P/Etub/q /XnEYzafYNkoOrYQMbqj6nFHYpYxymufPYjcGAjaRnVt2jxUzS3zPb6lpNjC6s5Oxrs0WYMRvbR dBvy+J/7pMy+teTA+x9T/E6ggkXyizQGe//4AxcBxcrhCKNqzem6rRKcxJLTefmrfU0CU2VW6uC 5x2JqlOAMSNtXM1AfGSytrxIFOr2S3XPEdTEP1QyOTNlKzTtGtrjaWkIbxQVZc7XyWa9Ggbdnl8 wkgYg373aI71Rh0ZOzmEr1tWX4M68Yz9HwoQbCiqMpeXkMBa3EZ9mW+HowhL506x5+1yPvl4rLU 90pIQxaV X-Proofpoint-GUID: NmMecPGQNEFV5Z6yet56qjNF4vqqAdRy X-Proofpoint-ORIG-GUID: 1xCeVzb0bz4EbY7yd5ySncyf5nvF03Hn X-Authority-Analysis: v=2.4 cv=Ao/u3P9P c=1 sm=1 tr=0 ts=68bab177 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=kj9zAlcOel0A:10 a=yJojWOMRYYMA:10 a=VwQbUJbxAAAA:8 a=7CQSdrXTAAAA:8 a=PE-dCK3ueRk4C2obWmcA:9 a=CjuIK1q_8ugA:10 a=a-qgeE7W1pNrGK8U0ZQC:22 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1117,Hydra:6.1.9,FMLib:17.12.80.40 definitions=2025-09-05_02,2025-09-04_01,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1011 phishscore=0 impostorscore=0 priorityscore=1501 spamscore=0 suspectscore=0 bulkscore=0 adultscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2507300000 definitions=main-2508300030 X-Rspamd-Queue-Id: 90DA3180003 X-Rspamd-Server: rspam04 X-Rspam-User: X-Stat-Signature: 56tuzaq4ngcexp4bahgxhsedzn5j7idq X-HE-Tag: 1757065618-998141 X-HE-Meta: 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 PrDW5Gcj jyFImAAMp+0WUTsxZsI/GZUIa+hnMSbQ/vejBgj6PR/IumdN/S+vmCIBleFqCJu0GE82lU3vDY0C8INzV2VW84MYYon88KZEvkL5QPPux/CF0uOfv/ICWM8ft9CqNdW78rTyq1cxd0+bZHlonxLQ9l3oNVZeTW7I6Y2GHep37q5+yipvl2E+uWpZir576Ff1035x6t8TbS3iZXf3iRTqaZyiTTmgcamngbeP0GD1auLUY0krGIYEnsfUKlzCzewabcT1Oq9uwATmBNzJEA4JQGqapHfuxZ56KBYj7csY5v5aaDeeFCooD66yvg5WBjYhsADj6BGJhQsJSVebhF0UxwHLbxzbedl6hEaPYIbQ0NTkVz+lAWUbzzk4oq034XjbismGDGpjzxe/clPc= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Sep 04, 2025 at 01:57:29PM +0100, Kevin Brodsky wrote: Hi Kevin, > When the lazy MMU mode was introduced eons ago, it wasn't made clear > whether such a sequence was legal: > > arch_enter_lazy_mmu_mode() > ... > arch_enter_lazy_mmu_mode() > ... > arch_leave_lazy_mmu_mode() > ... > arch_leave_lazy_mmu_mode() I did not take too deep - sorry if you already answered this. Quick question - whether a concern Ryan expressed is addressed in general case? https://lore.kernel.org/all/3cad01ea-b704-4156-807e-7a83643917a8@arm.com/ enter_lazy_mmu for_each_pte { read/modify-write pte alloc_page enter_lazy_mmu make page valid exit_lazy_mmu write_to_page } exit_lazy_mmu This example only works because lazy_mmu doesn't support nesting. The "make page valid" operation is completed by the time of the inner exit_lazy_mmu so that the page can be accessed in write_to_page. If nesting was supported, the inner exit_lazy_mmu would become a nop and write_to_page would explode. ... Thanks!