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[2003:cb:c72a:9100:23d2:3800:cdcc:90f0]) by smtp.gmail.com with UTF8SMTPSA id ffacd0b85a97d-3997f9957efsm2174115f8f.14.2025.03.21.04.37.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 21 Mar 2025 04:37:14 -0700 (PDT) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-trace-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, David Hildenbrand , Andrew Morton , Andrii Nakryiko , Matthew Wilcox , Russell King , Masami Hiramatsu , Oleg Nesterov , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , "Liang, Kan" , Tong Tiangen Subject: [PATCH v3 0/3] kernel/events/uprobes: uprobe_write_opcode() rewrite Date: Fri, 21 Mar 2025 12:37:10 +0100 Message-ID: <20250321113713.204682-1-david@redhat.com> X-Mailer: git-send-email 2.48.1 Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: YTptHw7-DG6Co-w0cPUrbdfnhrr2KVrc2vyUelLD03A_1742557036 X-Mimecast-Originator: redhat.com content-type: text/plain; charset="US-ASCII"; x-default=true Based on mm/unstable. Currently, uprobe_write_opcode() implements COW-breaking manually, which is really far from ideal. Further, there is interest in supporting uprobes on hugetlb pages [1], and leaving at least the COW-breaking to the core will make this much easier. Also, I think the current code doesn't really handle some things properly (see patch #3) when replacing/zapping pages. Let's rewrite it, to leave COW-breaking to the fault handler, and handle registration/unregistration by temporarily unmapping the anonymous page, modifying it, and mapping it again. We still have to implement zapping of anonymous pages ourselves, unfortunately. We could look into not performing the temporary unmapping if we can perform the write atomically, which would likely also make adding hugetlb support a lot easier. But, limited (e.g., only PMD/PUD) hugetlb support could be added on top of this with some tweaking. Note that we now won't have to allocate another anonymous folio when unregistering (which will be beneficial for hugetlb as well), we can simply modify the already-mapped one from the registration (if any). When registering a uprobe, we'll first trigger a ptrace-like write fault to break COW, to then modify the already-mapped page. Briefly sanity tested with perf probes and with the bpf uprobes selftest. v2 -> v3: * Fix missing folio_put() v1 -> v2: * "kernel/events/uprobes: uprobe_write_opcode() rewrite" -> hold GUP reference longer so we can see if the page is still mapped when performing the folio_walk -> Move anon-folio check -> Reshuffle / cleanup some related things RFC -> v1: * Use folio_walk and simplify the logic Cc: Andrew Morton Cc: Andrii Nakryiko Cc: Matthew Wilcox Cc: Russell King Cc: Masami Hiramatsu Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Ingo Molnar Cc: Arnaldo Carvalho de Melo Cc: Namhyung Kim Cc: Mark Rutland Cc: Alexander Shishkin Cc: Jiri Olsa Cc: Ian Rogers Cc: Adrian Hunter Cc: "Liang, Kan" Cc: Tong Tiangen [1] https://lkml.kernel.org/r/ZiK50qob9yl5e0Xz@bender.morinfr.org David Hildenbrand (3): kernel/events/uprobes: pass VMA instead of MM to remove_breakpoint() kernel/events/uprobes: pass VMA to set_swbp(), set_orig_insn() and uprobe_write_opcode() kernel/events/uprobes: uprobe_write_opcode() rewrite arch/arm/probes/uprobes/core.c | 4 +- include/linux/uprobes.h | 6 +- kernel/events/uprobes.c | 357 +++++++++++++++++---------------- 3 files changed, 187 insertions(+), 180 deletions(-) base-commit: a150906197a12c7b0f3f5efd844443bf98453efa Acked-by: Peter Zijlstra (Intel)