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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3E8C0C433EF for ; Thu, 9 Dec 2021 10:15:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233907AbhLIKTX (ORCPT ); Thu, 9 Dec 2021 05:19:23 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59312 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232856AbhLIKTW (ORCPT ); Thu, 9 Dec 2021 05:19:22 -0500 Received: from mail-pg1-x52e.google.com (mail-pg1-x52e.google.com [IPv6:2607:f8b0:4864:20::52e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 600ECC061746 for ; Thu, 9 Dec 2021 02:15:49 -0800 (PST) Received: by mail-pg1-x52e.google.com with SMTP id a23so67046pgm.4 for ; Thu, 09 Dec 2021 02:15:49 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=date:from:subject:to:cc:references:in-reply-to:mime-version :message-id:content-transfer-encoding; bh=uTtDFl4ylvWzOUxVw5Eo9EBEL+buH4qtkFmI+A3VVv0=; b=NQ9+kg5KOv5dp8pVp2G3I8lUbNXVG0gGlaVKBRUDptLxHDT3j6LoR5hi005x1rifX+ uA6bfveQG0dx3f3Pz+tdXHOtl8NoklpAuoTEXZUr+NSdbKoqLQlXdLMULNoJ0k9Rq6ZK SSEUIuBrDVN8GOsU/W4YMnlWzJypWUzwT+skDvkedX8UYzrYQHgnOiqAMWnKd0cRvd41 LM6mLgEdHygyZ72GDyz21c7VxxOdNMpIHcsRXabxpb4b5XhinlJaD+deOAZAo8o4HKKs KW2NnFS0VCtV+d/d3qC19MUMo6+woIuBgTEGVoOt7F/LCFRfUQLYO+GyaCpWHXIB2qEu Gbtw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:subject:to:cc:references:in-reply-to :mime-version:message-id:content-transfer-encoding; bh=uTtDFl4ylvWzOUxVw5Eo9EBEL+buH4qtkFmI+A3VVv0=; b=nFjplfrV4k/jnNt/Wz0vaFwBd9PKue+z3fOfqEmwKCqT3XtBY2Me1ykrwGRu/g5KIo FeeKD3u/6cFxRgfm+R5NYJ8THH437Y26YvMr6IVMnHZSGzxMlkk3L3cZJF5c/g245Rp/ Law9IJvWJ8nGSqZy4so1EHq8Kve5asPRuTJfEPilcL8UWT7kb5CTDIeKOirW/KC3vqyg D/NppjaN3q/a8utnbv3Cc4Q0hiz8sm/KxZnU2WU7yMMsllwYtlDgvH05jf8qLjF14D1C WJlwPjv39HkD3WC1usHmQwB+Jv7nd+ELg3L1+Ey6zZFpUor/+gMw/V+2ewiCMwObgPq/ KNEA== X-Gm-Message-State: AOAM532r4+q39L9EWdi4b1xyqMOjQQyEOZ5yCdWHNMVUw7eCufRjYfav sE1qqj+QYP9YTtDeQ/37Tg4= X-Google-Smtp-Source: ABdhPJwjI9kxYeG3xjcWudWWgMKJYeADbcpgkvYJNmVIASIiiFf9HmZhYN59I+Cd0HwMP0j9lYkm/w== X-Received: by 2002:a63:69c6:: with SMTP id e189mr32529626pgc.237.1639044949008; Thu, 09 Dec 2021 02:15:49 -0800 (PST) Received: from localhost (203-219-139-206.static.tpgi.com.au. [203.219.139.206]) by smtp.gmail.com with ESMTPSA id n6sm6227193pfa.28.2021.12.09.02.15.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 09 Dec 2021 02:15:48 -0800 (PST) Date: Thu, 09 Dec 2021 20:15:42 +1000 From: Nicholas Piggin Subject: Re: [PATCH v4 09/10] powerpc/mm: Convert to default topdown mmap layout To: "alex@ghiti.fr" , Benjamin Herrenschmidt , Christophe Leroy , Michael Ellerman , Paul Mackerras Cc: "akpm@linux-foundation.org" , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "linuxppc-dev@lists.ozlabs.org" References: In-Reply-To: MIME-Version: 1.0 Message-Id: <1639044621.jeow25j0pr.astroid@bobo.none> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Excerpts from Christophe Leroy's message of December 9, 2021 3:18 am: > Select CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT and > remove arch/powerpc/mm/mmap.c >=20 > This change provides standard randomisation of mmaps. >=20 > See commit 8b8addf891de ("x86/mm/32: Enable full randomization on i386 > and X86_32") for all the benefits of mmap randomisation. The justification seems pretty reasonable. >=20 > Comparison between powerpc implementation and the generic one: > - mmap_is_legacy() is identical. > - arch_mmap_rnd() does exactly the same allthough it's written > slightly differently. > - MIN_GAP and MAX_GAP are identical. > - mmap_base() does the same but uses STACK_RND_MASK which provides > the same values as stack_maxrandom_size(). > - arch_pick_mmap_layout() is almost identical. The only difference > is that it also adds the random factor to mm->mmap_base in legacy mode. >=20 > That last point is what provides the standard randomisation of mmaps. Thanks for describing it. Could you add random_factor to mmap_base for the legacy path for powerpc as a 2-line change that adds the legacy randomisation. And then this bigger patch would be closer to a no-op. Thanks, Nick