From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1FCA5D6552F for ; Tue, 26 Nov 2024 17:15:34 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 69B986B0085; Tue, 26 Nov 2024 12:15:33 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 64BD16B0088; Tue, 26 Nov 2024 12:15:33 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4EBBA6B008C; Tue, 26 Nov 2024 12:15:33 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 301FF6B0085 for ; Tue, 26 Nov 2024 12:15:33 -0500 (EST) Received: from smtpin03.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id D3ACCC0AD7 for ; Tue, 26 Nov 2024 17:15:32 +0000 (UTC) X-FDA: 82828897494.03.312270D Received: from mail-ed1-f44.google.com (mail-ed1-f44.google.com [209.85.208.44]) by imf15.hostedemail.com (Postfix) with ESMTP id 23325A0033 for ; Tue, 26 Nov 2024 17:15:25 +0000 (UTC) Authentication-Results: imf15.hostedemail.com; dkim=pass header.d=google.com header.s=20230601 header.b=kBsLl9zi; spf=pass (imf15.hostedemail.com: domain of jannh@google.com designates 209.85.208.44 as permitted sender) smtp.mailfrom=jannh@google.com; dmarc=pass (policy=reject) header.from=google.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1732641326; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=dqK5DtYfTpwNTtQIv9zMAjmqjKBcmKak3zeZPF/XA5E=; b=vneHxIkEPzLM3Ad9TsFsQl3MEUOxeudJAzsM5xAB9VM3Pu1tazAz1IPT9aT3XXSE4ypI4L W13XnNfu7iBIDGY2cAHUl42Gzsny7Vwh5mq70PCTS2Pds9T7njev/Gh6aMA+UE0KIaVhkm 5tAGjZu51dVkm7hjPagOWTr7vOrZWuY= ARC-Authentication-Results: i=1; imf15.hostedemail.com; dkim=pass header.d=google.com header.s=20230601 header.b=kBsLl9zi; spf=pass (imf15.hostedemail.com: domain of jannh@google.com designates 209.85.208.44 as permitted sender) smtp.mailfrom=jannh@google.com; dmarc=pass (policy=reject) header.from=google.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1732641326; a=rsa-sha256; cv=none; b=i59rnkr6XKXJYezHTUoj1AyUwzB7ZMINYQzRFTWQxkZ0vHNiAO92yQGfpHUJPMbrQq+bs4 7Mu3tWccnqdtIl5Jyyn9gW26Fv8D64gUG6tKGu3FWN4Iw7+KtJkyDSKUC8bNDxxPWLzbIx wIqdsNcCWmwHUijcUdDzuVUI1Yx0Z+s= Received: by mail-ed1-f44.google.com with SMTP id 4fb4d7f45d1cf-5d027dc53ccso11527a12.1 for ; Tue, 26 Nov 2024 09:15:30 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1732641329; x=1733246129; darn=kvack.org; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:from:to:cc:subject:date :message-id:reply-to; bh=dqK5DtYfTpwNTtQIv9zMAjmqjKBcmKak3zeZPF/XA5E=; b=kBsLl9ziZ6JoNyacScoHnd5vDx/5zmgJo5Dy2Lnm8ekBoNYGkD0/x0GSTxhf50ji+P DUbCNXU5HpzP/hEocrmkjJ3ESlBgoZPkJ4FYz/ZdjIeIbHJ9CR8/QxePKF8PMdZIh/rV OjMGqz4GaY0O46cn4J3AxarGKVNq4TNwv+aFH4s1fOvF/6t9RQTtB9b1eCEaKS/tERHK bbPiVZ9kZf+emCfyN2iXsS/Vb7aDuWZ/lFoWRFsft53sNsiHyjFYVKnrWWpJmORUIsjO sf/PyeQzJObkYHPqCg9cFUrmV1EGGEfTebtXd5aX90Q/hGDcbaIdlimBHlmiO99/6ITc Yb0w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1732641329; x=1733246129; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=dqK5DtYfTpwNTtQIv9zMAjmqjKBcmKak3zeZPF/XA5E=; b=PZCkKXLBgSru6SdPzGuVbu3Erktddr7mftrMVXuuSM03nO1ktoF9nft4F0pi7sYRwl hFQqdt187oFpegdYLxRbx8ZqW/VQoQ3Db+0o9e8M5meU+Cn4N9wbMACMDsz8L1bV0h0Z UzMdwmKnODWx0GokhGuBHCHBX2gIiDMGNk4zpd3sZCufmvyPEIcPy2SQI5NbmDMv5EyO j37B5ApwHXFjDxXwqtFW6q1rA98k60Wh5nzDWE8p6OAkpnB77QOvDcFPl/IuxsD7iyCK RYVukMmND9fS1TlYcJc+lPSZOtH9f1KKyI3R3QqZGCesTDJoKobiC2Z1kJVCQ4j/Xhhl v1Aw== X-Forwarded-Encrypted: i=1; AJvYcCV46rGWB/2Mx76IkNJNHYCl5MNMTn70+ktaIONgF8lw93WiVJsilhJnpHHrrUYv9X4OJDsHMSX93A==@kvack.org X-Gm-Message-State: AOJu0Yz7eqn6xmbwHaCop0JBD/LWuBC577wqCMpfF86nIn+2fz2THJdB F/ZCShekET1FfAWAGmpeknuor46B9TcG56TzZhBkLn4SxdlWYR1W3pbZTcHkbaG/Z6lfJwWbGPv aM+BYIaDQamo3KnwK3zt0srexnq+O4zcVxA+c X-Gm-Gg: ASbGncvW+PkQzXOzt01zRXxiJ3s1EB0qFFz0tpHL+LTeb+2xVRWeOM547irbK4BDVco gv1IMpWFxzVbD0YYYvElscPisXv5hgIjt6/C65OcS+0AcbJQEzZoksIyynms= X-Google-Smtp-Source: AGHT+IGZRocPcPSEtcuNErKj4DIDiJvXUShdMqtpfNV3ra7ee2dGktWA2YG43z+yQQWKUgLsr0A6/dsgXytzrSe8JgI= X-Received: by 2002:a05:6402:282:b0:5d0:6bc0:7706 with SMTP id 4fb4d7f45d1cf-5d06c91da98mr93597a12.6.1732641329016; Tue, 26 Nov 2024 09:15:29 -0800 (PST) MIME-Version: 1.0 References: <20241122-vma-v9-0-7127bfcdd54e@google.com> <20241122-vma-v9-8-7127bfcdd54e@google.com> In-Reply-To: <20241122-vma-v9-8-7127bfcdd54e@google.com> From: Jann Horn Date: Tue, 26 Nov 2024 18:14:52 +0100 Message-ID: Subject: Re: [PATCH v9 8/8] task: rust: rework how current is accessed To: Alice Ryhl Cc: Miguel Ojeda , Matthew Wilcox , Lorenzo Stoakes , Vlastimil Babka , John Hubbard , "Liam R. Howlett" , Andrew Morton , Greg Kroah-Hartman , Arnd Bergmann , Christian Brauner , Suren Baghdasaryan , Alex Gaynor , Boqun Feng , Gary Guo , =?UTF-8?Q?Bj=C3=B6rn_Roy_Baron?= , Benno Lossin , linux-kernel@vger.kernel.org, linux-mm@kvack.org, rust-for-linux@vger.kernel.org, Andreas Hindborg Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 23325A0033 X-Stat-Signature: fwm1bdm977cgjy1c68phzmb3udd8hdur X-Rspam-User: X-HE-Tag: 1732641325-194572 X-HE-Meta: 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 j5gd/0Ov x0xfZANI0cET7GtkWpyybm0N6KsSm+P7eNogzy9LxJG4FgnPpvfqu6bkwi8c1vOukXUh/JqirlqFX/+mngJdT8Fz/nZEO7f7yrU+l+aRRfcYo18ggezY2tqbcWxI1k+n97dk8mAkVAM0FyJBXSAmtx24zFV+9M7ve6OLmWUr+9FqA2Jkww0W70dsQn3N5FJodCmYLzLJBruPbRmndPu6iVOdnDCEf1j3MDmcEaBS0hGSGDpHJItINfct5kRREWJmZmt+TuydlU6AS8Go/5thPJZXHS9C5jP3Iuwgh X-Bogosity: Ham, tests=bogofilter, spamicity=0.000063, 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 Fri, Nov 22, 2024 at 4:41=E2=80=AFPM Alice Ryhl w= rote: > +impl CurrentTask { > + /// Access the address space of this task. > + /// > + /// To increment the refcount of the referenced `mm`, you can use `A= Ref::from`. > + #[inline] > + pub fn mm(&self) -> Option<&MmWithUser> { > + let mm =3D unsafe { (*self.as_ptr()).mm }; > + > + if mm.is_null() { > + None > + } else { > + // SAFETY: If `current->mm` is non-null, then it references = a valid mm with a non-zero > + // value of `mm_users`. The returned `&MmWithUser` borrows f= rom `CurrentTask`, so the > + // `&MmWithUser` cannot escape the current task, meaning `mm= _users` can't reach zero > + // while the reference is still live. > + Some(unsafe { MmWithUser::from_raw(mm) }) Maybe also add safety comments for these nitpicky details: kthreads can use kthread_use_mm()/kthread_unuse_mm() to change current->mm (which allows kthreads to access arbitrary userspace address spaces with copy_from_user/copy_to_user), but as long as you can't call into kthread_use_mm()/kthread_unuse_mm() from Rust code, this should be correct. If you do want to allow calls into kthread_use_mm()/kthread_unuse_mm() later on, you might have to gate this on a check for PF_KTHREAD, or something like that. Binary formats' .load_binary implementations can change current->mm by calling begin_new_exec(), but that's not an issue as long as no binary format loaders are implemented in Rust. > + } > + } > +} > + > // SAFETY: The type invariants guarantee that `Task` is always refcounte= d. > unsafe impl crate::types::AlwaysRefCounted for Task { > fn inc_ref(&self) { > > -- > 2.47.0.371.ga323438b13-goog >