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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 513FAC44501 for ; Thu, 16 Jul 2026 10:24:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=z7+pM5jkby4cO7IPGdPKP6foy3cGOmL3+UYyFsVki3w=; b=Ha1BM5EndhfwPAiivdvlb9BkmO QX5lM4CqBReRq/ePcdze2CUR/6AngTOrw7hMoyKZRr8GOEbPOGSzbBnShQQK1F80Gs5ZLVMLENmHW QL3loWUFvnXSOpWhYPITUlfr/cR5F+la+aNBZofv8c8uTFiLaWs7mVwdiaMrXhLJRAMwf3BkA44P5 uj4M1gLd7DhRlgxRmHm3pNQyaJJw8jC/xLWr7i9rNfMPohtUOSpKFav8jLEO5cHyGyOmqntXD6Ruf dj8i2SjRZOyWRsCFSAKXvRIs+r3WYEGl1Y15AMXNgfe5ObYCl2zvVp1BouGzC5XfSfj5DBN74AHNf 4DiU1MEQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wkJGd-0000000H0Ju-2oFu; Thu, 16 Jul 2026 10:24:35 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wkJGb-0000000H0J8-0Tf6; Thu, 16 Jul 2026 10:24:34 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id DEA931477; Thu, 16 Jul 2026 03:24:27 -0700 (PDT) Received: from [10.57.83.230] (unknown [10.57.83.230]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 182553F7B4; Thu, 16 Jul 2026 03:24:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1784197472; bh=khk7OVdasrmWElu7v+he5pwEjEyq3lY0VQWweIBUcxo=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=SWDF44sfS9ouTQyhsoNdjcWghv45qcZdrZRpeHggINaskI2QpA6EEqdwPjW+Vmzil Oyq849N1iPFY3DmI3306OC+qsEo5JxlkY3KFxgqlm9GhUkNprXodnPXqeKyEOXySIf HsuDVJWHrNHvd1lWMUDXxIJ2DVjDYvMciJe7gb58= Message-ID: Date: Thu, 16 Jul 2026 12:24:18 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 17/22] mm: pagewalk: drop redundant address check for kernel mm walks To: linux-mm@kvack.org Cc: Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Pasha Tatashin , Russell King , Catalin Marinas , Will Deacon , Ryan Roberts , linux-arm-kernel@lists.infradead.org, Huacai Chen , loongarch@lists.linux.dev, "James E.J. Bottomley" , Helge Deller , linux-parisc@vger.kernel.org, Madhavan Srinivasan , Michael Ellerman , linuxppc-dev@lists.ozlabs.org, Paul Walmsley , Palmer Dabbelt , Albert Ou , linux-riscv@lists.infradead.org, Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Gerald Schaefer , linux-s390@vger.kernel.org, "David S. Miller" , Andreas Larsson , sparclinux@vger.kernel.org, Richard Weinberger , Anton Ivanov , Johannes Berg , linux-um@lists.infradead.org, Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Andy Lutomirski , Peter Zijlstra , Ning Sun , x86@kernel.org, tboot-devel@lists.sourceforge.net, Ard Biesheuvel , Ilias Apalodimas , linux-efi@vger.kernel.org, Vishal Moola , Alistair Popple , "Matthew Wilcox (Oracle)" , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org References: <20260714-remove_pgtable_cdtor-v1-0-44be8a7685d7@arm.com> <20260714-remove_pgtable_cdtor-v1-17-44be8a7685d7@arm.com> From: Kevin Brodsky Content-Language: en-GB In-Reply-To: <20260714-remove_pgtable_cdtor-v1-17-44be8a7685d7@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260716_032433_239917_962FF997 X-CRM114-Status: GOOD ( 23.32 ) X-BeenThere: linux-um@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-um" Errors-To: linux-um-bounces+linux-um=archiver.kernel.org@lists.infradead.org On 14/07/2026 16:04, Kevin Brodsky wrote: > Commit 8b1cb4a2e819 ("mm/pagewalk: fix EFI_PGT_DUMP of > espfix area") made no-VMA page table walks use > pte_offset_kernel() for any address above TASK_SIZE. This avoided > pte_offset_map() validation on EFI page table dumps, where efi_mm > could walk x86 espfix PMDs that intentionally look bad to pmd_bad(). Sashiko rightly doesn't like this patch. Turns out 8b1cb4a2e819's commit message and the comment it added are narrower than what the problem really is: on x86, due to things like /sys/kernel/debug/page_tables/current_kernel, we may be walking kernel page tables even when walk->mm is a regular user mm. Just checking the mm is therefore not sufficient. Will replace this patch with a rewording of the comment to avoid suggesting the issue is specific to efi_mm. - Kevin > efi_mm is now marked with MMF_KERNEL, and no-VMA walks use > mm_is_kernel() to select pte_offset_kernel() for kernel mm's. As a > result we no longer need to handle the EFI_PGT_DUMP case explicitly.The > address check is therefore redundant for EFI_PGT_DUMP and makes the > condition harder to reason about. > > Remove the address check and associated comment; mm_is_kernel() > should be sufficient on its own. > > Tested by booting x86 QEMU with CONFIG_EFI_PGT_DUMP=y and reading > /sys/kernel/debug/page_tables/efi. > > Assisted-by: Codex:GPT-5.5 > Signed-off-by: Kevin Brodsky > --- > mm/pagewalk.c | 7 ++----- > 1 file changed, 2 insertions(+), 5 deletions(-) > > diff --git a/mm/pagewalk.c b/mm/pagewalk.c > index a3f47d1de3c5..0dd9d4ad9b68 100644 > --- a/mm/pagewalk.c > +++ b/mm/pagewalk.c > @@ -68,17 +68,14 @@ static int walk_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end, > if (walk->no_vma) { > /* > * pte_offset_map() might apply user-specific validation. > - * Indeed, on x86_64 the pmd entries set up by init_espfix_ap() > - * fit its pmd_bad() check (_PAGE_NX set and _PAGE_RW clear), > - * and CONFIG_EFI_PGT_DUMP efi_mm goes so far as to walk them. > */ > - if (mm_is_kernel(walk->mm) || addr >= TASK_SIZE) > + if (mm_is_kernel(walk->mm)) > pte = pte_offset_kernel(pmd, addr); > else > pte = pte_offset_map(pmd, addr); > if (pte) { > err = walk_pte_range_inner(pte, addr, end, walk); > - if (!mm_is_kernel(walk->mm) && addr < TASK_SIZE) > + if (!mm_is_kernel(walk->mm)) > pte_unmap(pte); > } > } else { >