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 CC733C8302F for ; Tue, 1 Jul 2025 10:34:27 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 609D28D0006; Tue, 1 Jul 2025 06:34:27 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 5BAB08D0001; Tue, 1 Jul 2025 06:34:27 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 482C98D0006; Tue, 1 Jul 2025 06:34:27 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 2EDB18D0001 for ; Tue, 1 Jul 2025 06:34:27 -0400 (EDT) Received: from smtpin01.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay02.hostedemail.com (Postfix) with ESMTP id C29AD123F9E for ; Tue, 1 Jul 2025 10:34:26 +0000 (UTC) X-FDA: 83615336532.01.5FD3F81 Received: from mail-ed1-f50.google.com (mail-ed1-f50.google.com [209.85.208.50]) by imf08.hostedemail.com (Postfix) with ESMTP id DF7D9160004 for ; Tue, 1 Jul 2025 10:34:24 +0000 (UTC) Authentication-Results: imf08.hostedemail.com; dkim=pass header.d=google.com header.s=20230601 header.b=DnEyUeLj; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf08.hostedemail.com: domain of jannh@google.com designates 209.85.208.50 as permitted sender) smtp.mailfrom=jannh@google.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1751366065; a=rsa-sha256; cv=none; b=NBUH6uHrqurDYftZvvecXTxXpKN0wcbxfla4KgxZ853mO8xEu6PLhn8IhJXeUGJIHPZyFc v8Z+/gXhlnJgyAn3eJDGZcffAU7H8oYptBcDZLY+1r4z5QxL4eeJ5PI89gUoX7KboGXs+I JlvomWClUKxbrQ6dlYz9ujwTxOA0ypc= ARC-Authentication-Results: i=1; imf08.hostedemail.com; dkim=pass header.d=google.com header.s=20230601 header.b=DnEyUeLj; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf08.hostedemail.com: domain of jannh@google.com designates 209.85.208.50 as permitted sender) smtp.mailfrom=jannh@google.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1751366065; 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=qp4bVSGoIFyW3QSZPFAFfubzk2+mLro6i9/ObDTSNoc=; b=768vZcIDqAhGIY7mrleq+oJpYsBkHj/ujSQnTQTs20YcGGp59JKS+/PAEhrtAVpto40cOw JwOslWbGviG0jstMCb+AaEiAV5DRmcenzpDVviQ3g5y0QBZywk16OjybenCFs82Q2qLjB2 mm3dzosZexCu8wQsIz9U/N4D+OsJX4Y= Received: by mail-ed1-f50.google.com with SMTP id 4fb4d7f45d1cf-5f438523d6fso6620a12.1 for ; Tue, 01 Jul 2025 03:34:24 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1751366063; x=1751970863; 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=qp4bVSGoIFyW3QSZPFAFfubzk2+mLro6i9/ObDTSNoc=; b=DnEyUeLj3tVVm/bNedfHRW8u9JQt0vxPg/239GPYKB1F05nNOKMxidvm0Lh/xP1tbK EPh8nTIW62zg1EehovCWm312R+573rK5FHncTC1Q3gmloYJYTdG4KyZWGw8O+T3D6Ggn igpULmQ7mHEvWf4fWmUGryZwylCPTYj5oNCUO67IQ07q4PNyvKoDaStGdW8tKR5FjICP WBmHeFdhPzacfozye7hki2Zk2MOQ+WEZKWMXR4bZqQIl/9On54ZSB3b7vZAYmrt44INY xTWzpOAxKzQ4NoAzKuMrAAocVDPt7cqoSOKlsxI1gUlEavmtRo/ZI1Ko7XuAEluiwa2j f8RQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1751366063; x=1751970863; 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=qp4bVSGoIFyW3QSZPFAFfubzk2+mLro6i9/ObDTSNoc=; b=AQuQWIxKvS7mx8s27upkgmwAxI5iNKVrjSj7SEDn2gnzoBcVdvQlntn9VqKnDkm5aX btnbVFgotNE67KXUZsCisrEgmXdXzWOFq6yVh5AbtFk0avhjs/vtkklEBr04bo/RplxH aciPlanbUKs/U3O7mdZx2jPGnM4SjReJfvwUeUYKUfLq1pHzSH918okOMAXZAnWfb7Ic apvdByynX+z0X6cfARZRW1rs+HzIjopV8MGi4NDhnSjX2HyvvfxsT9pHtNknvwHRLzwP VNnMUJcIJGXegkS4AoSr+4YisqXYKGi6NaoAIzbbvABxkTtwo6gtAMJy61I8hgSBMd6i oN/A== X-Forwarded-Encrypted: i=1; AJvYcCVxlhjQmViyYfWqofteR4J0s4y2xPbqTIEsqOWP5BCSmFaMJyJWeLOAnCbZwVX8NDtwmgGx8lD0Gg==@kvack.org X-Gm-Message-State: AOJu0YxL9Z0jM5RZyGi8fiLadBQp+BsCo8IWc35GWxLLNRcV1u8OQtQO togeFHdmd1CU9j3Rl0fjdkk0TshHk75uGYD7nMAMGPFAGAAuHoB7ws/pTXO0gdfwuTo6E+dWvDy i2B7j6DdtqgUTmTsWXpkDy3F7uouDdya8kZEvJfas X-Gm-Gg: ASbGncuyVABOOtYuxzbN0XwiFeF1aPmtvXg0s9O+7yVG5ef+lo+4t1TTo7V8yqIhXH1 KlB8ANwPtygTEuOzkKlNBlBSguK3+vTLrZb0IEoGa5wZYJcIvxsA81/en/KDh6cn6UDd0BGoD4T W9is+EqorRf7LizFmgtrJf+s1iMm/tux1ScpXaCTUZkdu+X99UN5QVeQM8ujwPjMz0/dd2OZQ= X-Google-Smtp-Source: AGHT+IECcsWBgg3PF6i48r44nlp9IbtTj/EJFncm5u1sICXIyrAefpX9CpH2gIQ3ueQKjUmMICOM70+9nQx4/JJS8NA= X-Received: by 2002:aa7:db87:0:b0:60c:bf83:65fd with SMTP id 4fb4d7f45d1cf-60e38aaa441mr50137a12.7.1751366062867; Tue, 01 Jul 2025 03:34:22 -0700 (PDT) MIME-Version: 1.0 References: <20250630-x86-2level-hugetlb-v1-1-077cd53d8255@google.com> <9179e1cd-d635-4e70-931e-4a85c2e6932b@intel.com> In-Reply-To: <9179e1cd-d635-4e70-931e-4a85c2e6932b@intel.com> From: Jann Horn Date: Tue, 1 Jul 2025 12:33:46 +0200 X-Gm-Features: Ac12FXxhb8kBzQck0JMDVfWECd6qOpwCqgTE5nperjslnwlAJZeksR8-H6YaZhA Message-ID: Subject: Re: [PATCH] x86/mm: Disable hugetlb page table sharing on non-PAE 32-bit To: Dave Hansen Cc: Dave Hansen , Andy Lutomirski , Peter Zijlstra , Muchun Song , Oscar Salvador , Vitaly Chikunov , linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: DF7D9160004 X-Stat-Signature: nneam38fdm6b18edc6bgcudogsjz7q3a X-Rspam-User: X-HE-Tag: 1751366064-837549 X-HE-Meta: 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 Frsdc4xg UBc1g/3kkP4ln0mcCtyWlHR0d/Scx8I5PELfw92No63G8ricUsDj0UxVolga06+je6BgA/1WKfttbc32qC5LCNwo2oKj8OcRzKanRziz2B547yRjX+kzMM/sFhJLgiXYq/gSpJh5Gn5PZ/gZdrGM5qukA0zOKYCF3a7HNnyO0RuSt9VCzr4NVqoFkR6MVzQor2yeeH/h2U8SFd7hng11P4ljQLw== 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 Mon, Jun 30, 2025 at 10:39=E2=80=AFPM Dave Hansen wrote: > On 6/30/25 12:07, Jann Horn wrote: > > --- a/arch/x86/Kconfig > > +++ b/arch/x86/Kconfig > > @@ -147,7 +147,7 @@ config X86 > > select ARCH_WANTS_DYNAMIC_TASK_STRUCT > > select ARCH_WANTS_NO_INSTR > > select ARCH_WANT_GENERAL_HUGETLB > > - select ARCH_WANT_HUGE_PMD_SHARE > > + select ARCH_WANT_HUGE_PMD_SHARE if PGTABLE_LEVELS > 2 > > select ARCH_WANT_LD_ORPHAN_WARN > > select ARCH_WANT_OPTIMIZE_DAX_VMEMMAP if X86_64 > > select ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP if X86_64 > > Does pmd sharing really even work on 32-bit? Just practically, you only > ever have 3GB of address space and thus 3 possible PGDs that can be used > for sharing (with the 3:1 split configured). You presumably need *some* > address space for the binary to even execve(). The vdso and friends go > somewhere and we normally don't let anything get mapped at 0x0. > > I think that leaves _maybe_ one slot. > > Barring something some specific and compelling actual use case, this > should probably just be: > > select ARCH_WANT_HUGE_PMD_SHARE if X86_64 Yeah, makes sense. I was also thinking that it would be more reasonable to restrict this to 64-bit only, but figured it would be less risky to make this more specific change. But now that I think about it, it's not like stuff is actually going to break from this change, worst case the kernel memory usage goes up a bunch in a very unlikely configuration... so yeah, I guess I'll resend this later with "if X86-64".