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Mon, 10 Mar 2025 13:04:08 -0400 X-MC-Unique: qcA6nO9WNJ6cidPgFWXLFQ-1 X-Mimecast-MFC-AGG-ID: qcA6nO9WNJ6cidPgFWXLFQ_1741626245 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 3444E1800349; Mon, 10 Mar 2025 17:04:03 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.45.224.34]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with SMTP id 310AD1956094; Mon, 10 Mar 2025 17:03:53 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Mon, 10 Mar 2025 18:03:32 +0100 (CET) Date: Mon, 10 Mar 2025 18:03:21 +0100 From: Oleg Nesterov To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-trace-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, Andrew Morton , Matthew Wilcox , Russell King , Masami Hiramatsu , 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: Re: [PATCH -next v1 3/3] kernel/events/uprobes: uprobe_write_opcode() rewrite Message-ID: <20250310170320.GC26382@redhat.com> References: <20250304154846.1937958-1-david@redhat.com> <20250304154846.1937958-4-david@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250304154846.1937958-4-david@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 X-Stat-Signature: e985cf19kgk1i7b6dwaufbnwrmdrx1hk X-Rspamd-Server: rspam05 X-Rspam-User: X-Rspamd-Queue-Id: D4FD140011 X-HE-Tag: 1741626251-853434 X-HE-Meta: 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 8hNw7vZp BQAI7Ec770/FcT3yZ3Unk3l9GXHqE3BsddH60Awzi2uZzmDRJDnStWQjrwQ7/OPDYm+3A+yjby5oKsVBPlkONx9YZOArD4s0C+6CPv35LM9Gcte/J3yp7X7lXUjtEpYBNwf3Fn0804CncFjD1oloyUbQlWpENbel7uYG2EsMC4RulYgn1fcCHuPAWZn02bK+U426OdmrgbH6MbSwclMroHefkMfY6XgyVJcgxzGvbcK2gtU0P/T/9+e8pacATKC5RoZ541BNs9s5NAszyI6M3zIfM4ucIfWrEnUpQejzikCJt8M4KScPvGme3bAiPKqKP4oIoIL8TegQPBrbXlVs3A2qZ7pRbBhIQ0+YG+PsGF4t46yk= 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 03/04, David Hildenbrand wrote: > > uprobe_write_opcode() does some pretty low-level things that really, it > shouldn't be doing: Agreed. Thanks again for doing this. David, as I said, I can't review. I don't understand this mm/folio magic with or without your changes. However. With your changes the code looks "better" and more understandable to me. So I'd vote for your patches even if I can't ack them. But I'd like to ask some stupid (no, really) questions. __uprobe_write_opcode() does: /* We're done if we don't find an anonymous folio when unregistering. */ if (!folio_test_anon(folio)) return is_register ? -EFAULT : 0; Yes, but we do not expect !folio_test_anon() if register == true, right? See also below. /* Verify that the page content is still as expected. */ if (verify_opcode(fw->page, opcode_vaddr, &opcode) <= 0) { set_pte_at(vma->vm_mm, vaddr, fw->ptep, fw->pte); return -EAGAIN; } The caller, uprobe_write_opcode(), has already called verify_opcode(), why do we need to re-check? But whatever reason we have. Can we change uprobe_write_opcode() to "delay" put_page() and instead of /* Walk the page tables again, to perform the actual update. */ folio = folio_walk_start(&fw, vma, vaddr, 0); if (folio) { ret = __uprobe_write_opcode(vma, &fw, folio, opcode_vaddr, opcode); folio_walk_end(&fw, vma); } else { ret = -EAGAIN; } do something like /* Walk the page tables again, to perform the actual update. */ ret = -EAGAIN; folio = folio_walk_start(&fw, vma, vaddr, 0); if (folio) { if (fw.page == page) { WARN_ON(is_register && !folio_test_anon(folio)); ret = __uprobe_write_opcode(vma, &fw, folio, opcode_vaddr, opcode); } folio_walk_end(&fw, vma); } ? Once again, I am not trying to review. I am trying to understand the basics of your code. Thanks, Oleg.