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 F2782CFA45C for ; Wed, 23 Oct 2024 18:34:01 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 669BF6B0088; Wed, 23 Oct 2024 14:34:01 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 619FE6B008C; Wed, 23 Oct 2024 14:34:01 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4E1AD6B0093; Wed, 23 Oct 2024 14:34:01 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 2C7306B0088 for ; Wed, 23 Oct 2024 14:34:01 -0400 (EDT) Received: from smtpin24.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id EFF4CAC603 for ; Wed, 23 Oct 2024 18:33:25 +0000 (UTC) X-FDA: 82705715736.24.CEF1F92 Received: from mail-oo1-f45.google.com (mail-oo1-f45.google.com [209.85.161.45]) by imf20.hostedemail.com (Postfix) with ESMTP id 9C53A1C001F for ; Wed, 23 Oct 2024 18:33:37 +0000 (UTC) Authentication-Results: imf20.hostedemail.com; dkim=pass header.d=chromium.org header.s=google header.b="i7g8BON/"; dmarc=pass (policy=none) header.from=chromium.org; spf=pass (imf20.hostedemail.com: domain of jeffxu@chromium.org designates 209.85.161.45 as permitted sender) smtp.mailfrom=jeffxu@chromium.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1729708315; a=rsa-sha256; cv=none; b=pPp4e5yYC8WR0to6gO8cqNggdiguR5ulI2OPn78WjF4KMN9GmTi8X93S3i+W2u50EdwJLf x3L0x6Ba+CTMHHT6CtSdOXZbeHRwu52wBrJxnPS7bBKly0cY5oAAPIEzhUbQlJWFpS3jnn RH2idJLI+qlPv2Bxxu9rwkeDK2CMCRI= ARC-Authentication-Results: i=1; imf20.hostedemail.com; dkim=pass header.d=chromium.org header.s=google header.b="i7g8BON/"; dmarc=pass (policy=none) header.from=chromium.org; spf=pass (imf20.hostedemail.com: domain of jeffxu@chromium.org designates 209.85.161.45 as permitted sender) smtp.mailfrom=jeffxu@chromium.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1729708315; 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=TVm15+JO2o8mM+w0yinyleN/ZVNf1YYgHDbnm3S0yro=; b=IfXnk2KkPQafF2+lSbQzyLNGEEMLpZC1YAM76fM8V8rUz8JIRLj0l9vw/Le0NtihWIWsFO Gxsfyn0tf957Vqgb61PfWuKPLaE9URCogwCwVTSxGEo/hXxQ9EYlNYq0zoNlEs2ZQEVbd3 iTLs4UIYtOzZUbuoqQyb1g8BnpSlyYU= Received: by mail-oo1-f45.google.com with SMTP id 006d021491bc7-5ebeca94c87so1147eaf.2 for ; Wed, 23 Oct 2024 11:33:58 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; t=1729708438; x=1730313238; 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=TVm15+JO2o8mM+w0yinyleN/ZVNf1YYgHDbnm3S0yro=; b=i7g8BON/ISKrzc8PTWL7jzXDXoPw9JDO0R9JsG4mXCDKuqA4Rqjmar1f8JBriKwR3k LrGs9jC5Zv0emmRSbvnLVOJtlZCmrNlVYL1yDOK3HCO/nS3xBqmGkIRjcrkooJXTRS2W mbAIsyNbz2+9mvwOUE/u3QDVX8n6qT/mA/9Y8= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1729708438; x=1730313238; 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=TVm15+JO2o8mM+w0yinyleN/ZVNf1YYgHDbnm3S0yro=; b=ro71MQ1hc61dbIqX4Jk/MnPQJCk/rsRIgqtIxNaYlL7hyejkOVcy18tkZV52GV3auK 86EvNKUG9r8WuEtMlMkwu7oJPwPrtzSmrzIb2tQSgbYv0Pf+FLDwYD2uWGsosaZMz9/y aChu8nR/hokV88rrsFqgtq6LS+clNeGhFF7/9ZL7R1rl3A+XXbpTzP+uJ7YfRj0cPTze tFxkuxQIHuoPkusueYkUHG9wPkZVnHD2O1Fn8jRtjF2uNo3qaKhsCnl2mlo7hwvTOhz3 WS9Lomw7xsd44GTddRxLgKGYYUBBVNgvyUPNZMqSyme2xMG/Y/ZHzMZfXnXWEnh8GeMc PSkA== X-Forwarded-Encrypted: i=1; AJvYcCWejo8e1N2XCGeWtRIwcCtqFG3uNVgCzBPvqh32rcz+n55MXExB+UOH7qErJCQ7PW5ZonOksWIrtw==@kvack.org X-Gm-Message-State: AOJu0YzbdODLaulCkJFDJvxgmBW8n60Dni1SDfPfm0yylFeNvEY35LD1 nwbT8EBaoeIdthwYdwGef+uMY/l5q01/InzDP6ZDMHnPJ/4fhYOE5gkGUpwfzxtuMVhUb0DN4jI aJ8VoQGIBB5mBWqJ0ovwCsheNPduSqXfxFP8X X-Google-Smtp-Source: AGHT+IHLGbkE5Oo4IYlY3tWegFIJ6lm7Wf/IIJ6qevixwoPKrt15CKBR9bfEkXM+gXkwnZyxMgOtkG3lSgqMgDT/5dQ= X-Received: by 2002:a05:6870:5590:b0:27b:b2e0:6af with SMTP id 586e51a60fabf-28ccb40e51emr1031801fac.2.1729708438196; Wed, 23 Oct 2024 11:33:58 -0700 (PDT) MIME-Version: 1.0 References: <20241017005105.3047458-1-jeffxu@chromium.org> <20241017005105.3047458-2-jeffxu@chromium.org> <5svaztlptf4gs4sp6zyzycwjm2fnpd2xw3oirsls67sq7gq7wv@pwcktbixrzdo> <8f68ad82-2f60-49f8-b150-0cf183c9cc71@suse.cz> In-Reply-To: <8f68ad82-2f60-49f8-b150-0cf183c9cc71@suse.cz> From: Jeff Xu Date: Wed, 23 Oct 2024 11:33:46 -0700 Message-ID: Subject: Re: [PATCH v1 1/2] mseal: Two fixes for madvise(MADV_DONTNEED) when sealed To: Vlastimil Babka Cc: Pedro Falcato , akpm@linux-foundation.org, keescook@chromium.org, torvalds@linux-foundation.org, usama.anjum@collabora.com, corbet@lwn.net, Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com, jeffxu@google.com, jorgelo@chromium.org, groeck@chromium.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, jannh@google.com, sroettger@google.com, linux-hardening@vger.kernel.org, willy@infradead.org, gregkh@linuxfoundation.org, deraadt@openbsd.org, surenb@google.com, merimus@google.com, rdunlap@infradead.org, stable@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 9C53A1C001F X-Stat-Signature: t991ogebz639b1zik3fj8ths57qn5zcn X-Rspam-User: X-HE-Tag: 1729708417-302843 X-HE-Meta: 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 kSdP29+d XSXpbIRQw/5CqfT9g2MTiCvHTIHoaVIN8bLmBpLwCcQvQTN3yZHX9Bd5YacqOdur4kY68+0MfnOqRfpHd8VWrqQGm31S/zaSinXbXyf46+kav3DJ7aIXFqz1dBZy/bbwaHc4P0nYa9TmytteucgIk/N/G/AbNpJc8fYipDvpEkFjp6dPH9keWJGHo3qInuNX9Ya/P1msL+ADtFbvf9fMAod6FnHCGDeT0/ZsAqKRLaQF+ZC24sihjqyH271Qf0+EV+x70ZG1qgrIHzlonRpLlvTQ7uv5Y7oojWfoxaGzxjscgnPqXsPD4QCjBLjYY9peGqiLVToatP3hKL6QKfyZZCGyBoA== 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: Hi Vlastimil On Tue, Oct 22, 2024 at 8:55=E2=80=AFAM Vlastimil Babka wr= ote: > > On 10/17/24 22:57, Jeff Xu wrote: > > On Thu, Oct 17, 2024 at 1:49=E2=80=AFPM Pedro Falcato wrote: > >> > > >> > > > For file-backed, private, read-only memory mappings, we previous= ly did > >> > > > not block the madvise(MADV_DONTNEED). This was based on > >> > > > the assumption that the memory's content, being file-backed, cou= ld be > >> > > > retrieved from the file if accessed again. However, this assumpt= ion > >> > > > failed to consider scenarios where a mapping is initially create= d as > >> > > > read-write, modified, and subsequently changed to read-only. The= newly > >> > > > introduced VM_WASWRITE flag addresses this oversight. > >> > > > >> > > We *do not* need this. It's sufficient to just block discard opera= tions on read-only > >> > > private mappings. > >> > I think you meant blocking madvise(MADV_DONTNEED) on all read-only > >> > private file-backed mappings. > >> > > >> > I considered that option, but there is a use case for madvise on tho= se > >> > mappings that never get modified. > >> > > >> > Apps can use that to free up RAM. e.g. Considering read-only .text > >> > section, which never gets modified, madvise( MADV_DONTNEED) can free > >> > up RAM when memory is in-stress, memory will be reclaimed from a > >> > backed-file on next read access. Therefore we can't just block all > >> > read-only private file-backed mapping, only those that really need t= o, > >> > such as mapping changed from rw=3D>r (what you described) > >> > >> Does anyone actually do this? If so, why? WHYYYY? > >> > > This is a legit use case, I can't argue that it isn't. > > Could the same effect be simply achieved with MADV_COLD/MADV_PAGEOUT? Tha= t > should be able to reclaim the pages as well if they are indeed not used, = but > it's non-destructive and you don't want to allow destructive madvise anyw= ay > (i.e. no throwing away data that would be replaced by zeroes or original > file content on the next touch) so it seems overall a better fit for seal= ed > areas? > Thanks for the suggestion. This opens a new way to solve this, I need to do some research and testing to verify the solutions work for us. I will respond after I'm done with those. Best regards, -Jeff