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Fri, 1 May 2026 06:41:35 -0400 (EDT) Date: Fri, 1 May 2026 11:41:30 +0100 From: Kiryl Shutsemau To: akpm@linux-foundation.org, rppt@kernel.org, peterx@redhat.com, david@kernel.org Cc: ljs@kernel.org, surenb@google.com, vbabka@kernel.org, Liam.Howlett@oracle.com, ziy@nvidia.com, corbet@lwn.net, skhan@linuxfoundation.org, seanjc@google.com, pbonzini@redhat.com, jthoughton@google.com, aarcange@redhat.com, sj@kernel.org, usama.arif@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, kvm@vger.kernel.org, kernel-team@meta.com Subject: Re: [PATCH 10/14] mm/pagemap: add PAGE_IS_ACCESSED for RWP tracking Message-ID: References: <20260427114607.4068647-1-kas@kernel.org> <20260427114607.4068647-11-kas@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260427114607.4068647-11-kas@kernel.org> X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 1DA8B140004 X-Stat-Signature: bz41939f1nnxi3xt3z1b3pbhxijrkceo X-Rspam-User: X-HE-Tag: 1777632099-877518 X-HE-Meta: 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 QY0bE8xz 8N3Uz3100kfvaAF31nvmpI1vdd90SbiX+vB7tTQTdyjsA557LtMvvw1jhCZI+om+wtQYJujRLXWCA/jMP+wOMPko7ZIxyveeNuVjKEKGMprGFtWVaQZvsJoaoHguW5pueDnhf+TQprDJssVDpuG7RGInGqf95pK0/kcanZmwAaANrfGbZ65Tf/ngMVyv51tCq7UyhIT6pv4SPvYQ50torb8h6arAUu5zFVs9GK1wJOGZaOdt1d7D+2z2BILO5P0S5oaAQVpbdrqzascwpS+igYQpcN5w3BtYV+gcIBeEabqupne2F9zj84cT7vQnHQJf61bco1+cq1XfBTRdwBBZbZiwX4XnD8YVlxztARr4lxiSuTUD2Eg0WXG8rWhwlUl9+mXcRcVmxeqf79JUTgP15ofVSf76KTZbv9o0M Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: sashiko.dev -- https://sashiko.dev/#/patchset/20260427114607.4068647-1-kas@kernel.org -- wrote: > commit 6d6b8f986b2959f8ae0932deccc5afa4ec485813 > Author: Kiryl Shutsemau (Meta) > Subject: mm/pagemap: add PAGE_IS_ACCESSED for RWP tracking [ ... ] > Does this new PAGE_IS_ACCESSED tracking correctly support the atomic > read-and-reset workflow (PM_SCAN_WP_MATCHING) for RWP VMAs? [ ... ] > Since WP and RWP are mutually exclusive per VMA, userfaultfd_wp_async() and > userfaultfd_wp_use_markers() will return false for RWP VMAs, causing > pagemap_scan_test_walk() to return 1 and skip the VMA. [ ... ] > Because these loops hardcode a check against PAGE_IS_WRITTEN, and RWP VMAs > now populate PAGE_IS_ACCESSED instead, this check will always evaluate to > true for RWP. As a result, it looks like make_uffd_wp_pte() and > make_uffd_wp_pmd() will be silently skipped, preventing the atomic > reset of the tracking bits. > Would it make sense to update both the wp_allowed check and the hardcoded > PAGE_IS_WRITTEN checks to accommodate PAGE_IS_ACCESSED for RWP VMAs? PM_SCAN_WP_MATCHING is the atomic read-and-reset flavour and is implemented for the WP marker only. The silent-skip on PM_SCAN_WP_MATCHING + RWP VMA is not intended Will fold this fixup if (userfaultfd_rwp(vma) && (p->arg.flags & PM_SCAN_WP_MATCHING)) return -EINVAL; We can add similar operation for RWP later if there's a use-case. -- Kiryl Shutsemau / Kirill A. Shutemov