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Tue, 27 Jan 2026 15:51:38 GMT Received: from smtpav01.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 4FDCE20040; Tue, 27 Jan 2026 15:51:38 +0000 (GMT) Received: from smtpav01.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 1F2062004B; Tue, 27 Jan 2026 15:51:38 +0000 (GMT) Received: from tuxmaker.boeblingen.de.ibm.com (unknown [9.87.85.9]) by smtpav01.fra02v.mail.ibm.com (Postfix) with ESMTPS; Tue, 27 Jan 2026 15:51:38 +0000 (GMT) Date: Tue, 27 Jan 2026 16:51:36 +0100 From: Alexander Gordeev To: Andrew Donnellan Cc: linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, Pasha Tatashin , Andrew Morton , Madhavan Srinivasan , Nicholas Piggin , Rohan McLure , Christophe Leroy , Alexandre Ghiti , x86@kernel.org, Nicholas Miehlbradt , Sweet Tea Dorminy , Andrew Donnellan , Srish Srinivasan , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org Subject: Re: [PATCH v18 10/12] powerpc/mm: Implement *_user_accessible_page() for ptes Message-ID: <20260127155136.2808076Add-agordeev@linux.ibm.com> References: <20251219-pgtable_check_v18rebase-v18-0-755bc151a50b@linux.ibm.com> <20251219-pgtable_check_v18rebase-v18-10-755bc151a50b@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; 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> +} We looked into implementing this for s390 and for us the only possible user vs kernel entry attribute is comparing mm to init_mm. The generic code already does that, but I am not sure whether such check alone is enough. But it occured to me that we could implement e.g. ARCH_SUPPORTS_PTC_USER_PAGE that adds an extra field to struct page_table_check: struct page_table_check { atomic_t anon_map_count; atomic_t file_map_count; #ifdef CONFIG_ARCH_SUPPORTS_PTC_USER_PAGE bool user_page; #endif }; Page Table Extensions already used by PTC, so that would fit pretty natural. Once a page is mapped into a user process it would be marked as user_page, while p{te,md,ud}_user_accessible_page() could go generic: static inline bool pte_user_accessible_page(pte_t pte, unsigned long addr) { return pte_present(pte) && page_table_check_is_user_page(pte); } ... I guess, many architectures without viable p.._user() support could benefit from that. But I am not sure whether is it doable, so opinions are very welcomed! Thanks!