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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> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251219-pgtable_check_v18rebase-v18-10-755bc151a50b@linux.ibm.com> X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMTI3MDEyOSBTYWx0ZWRfXxChMywYP3CXN le5d6yn3Qq6MfjN6zC+Z+DQqleCzkUqKSkhMwpJSnn1Mj3zS2dO0nICsNnXEMtWsE3vyb83rzjQ 6kso4VpQ4wBoGpfXa+uDicwe3s/Tx9G27+lBkSjIdnBpBe924kovkU2wInK8zp4fCnVcBOZS31H BJ3DIi34TvoRR/5d3SQODO1mtpcggsmfvH/oLD96EUws0DAq+gksrBtgsBJS82RwOsHFmTzrNBL CNwOe0QD3sOFuH+hrRzC0HuLjsyg7NKVHQVFym8CqHd55vAIbLaoGLE/k7/e/ZOrw+hMYWVP7oQ 3uUxUrs0HYHgzU6E9dLRct4A1ePYLRq2MVcmQ4XlAiQw0ogB0VlRgK8V/qrltGoxEmwPlQvaIpZ oDSvwJEhdafxFukf2IRJrEZNbsOh1QhzlSOcS3BDkUFas4hDHNqKbsmPKpZG1pCe2JqB0joy895 KqtIgfb/A4B51Vjsq2g== X-Proofpoint-GUID: 8EJeeV34r0_XNIY9EmhfW46Wh100FMUs X-Proofpoint-ORIG-GUID: Bk5rloqyZadRkxusHYTPbD17s7SpVN9w X-Authority-Analysis: v=2.4 cv=X+Vf6WTe c=1 sm=1 tr=0 ts=6978df10 cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=kj9zAlcOel0A:10 a=vUbySO9Y5rIA:10 a=VkNPw1HP01LnGYTKEx00:22 a=cPWeadVanShsLn6B-a8A:9 a=CjuIK1q_8ugA:10 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-01-27_03,2026-01-27_03,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 suspectscore=0 impostorscore=0 lowpriorityscore=0 clxscore=1011 spamscore=0 adultscore=0 malwarescore=0 bulkscore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2601150000 definitions=main-2601270129 On Fri, Dec 19, 2025 at 04:09:42AM +1100, Andrew Donnellan wrote: Hi All, ... > Page table checking depends on architectures providing an > implementation of p{te,md,ud}_user_accessible_page. ... > +static inline bool pte_user_accessible_page(pte_t pte, unsigned long addr) > +{ > + return pte_present(pte) && !is_kernel_addr(addr); > +} 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!