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 59463F4198E for ; Wed, 15 Apr 2026 10:35:23 +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=am9Vfb1Aq580mnQo1cyYfFVKDwtcUwL0M+34cRZgLu0=; b=htxPEPS+DTg3AUhibB90lpkXdJ Pz5C9g/lekarGCxS4puO+WS+H88zDAIqj2F1eZ4fqw+p0aMSrP/QYU42MrXOXAnRn6PcbimjzCQJF rk+rvSi8A74PoeBbMXfpLgCcs0c2jHZ7+zSBzc6ucPSFhErxGK+SfEgo79CyHPal50j1+ANDds1Dm 8i+rp7bW5/pZVEgX79Q8hAoeyZpI+3iaayf2Up+iyZDIKgZDG+cafg4dpiepKuGrgd228A2z07neF TYq9SZWiKo4sZBC6anGS5v3xleY8dmdG+R3rV2nJTzvGwLQ14W7wENLfExJ8pT5ZTWstVqqhfVbWc 00kZX3KA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1wCxaX-00000000yYY-0kUT; Wed, 15 Apr 2026 10:35:17 +0000 Received: from sea.source.kernel.org ([2600:3c0a:e001:78e:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1wCxaV-00000000yYD-12Dq for linux-arm-kernel@lists.infradead.org; Wed, 15 Apr 2026 10:35:16 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id 66C1F44491; Wed, 15 Apr 2026 10:35:14 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EECF4C2BCB3; Wed, 15 Apr 2026 10:35:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776249314; bh=bpHgcNl4FYMb3tMxE2yHLnHeP4ny/KqKAE26kXtowaQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=c0X1iM/loYQV+lM9Y7nboPQ5AI057tcs4b3NzAj+4Ek9Mgu7fDkzUIT4bbM9KSX2G XVawRbC0AKM05vBRWJMZWLNgk2qDYdhQdB5GpVQBGYgZpWu66sjDgz6f9RrRnbqgWJ m6ays8iGIBJ6yqow4uNHPsK5Lix/zhsvs7/q/qc8015Ki9N9YyYJvj0b7V6NOr0qoY s3r1xNWSe24u7FGHpMdykAN7BkR8hh/cp8OsqbQTRE7zVd9kToPNuXO6Tgo+OurmpY 2ZFjTof4Gzk32YdqX13IeddI/nNkWhEVd0oKNBs9/95fiT5m/8uBmxrRoQWk1jpgq9 U7ZE/jfalFfIg== Message-ID: Date: Wed, 15 Apr 2026 12:35:07 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC V1 07/16] arm64/mm: Convert READ_ONCE() as p4dp_get() while accessing P4D To: Anshuman Khandual , linux-arm-kernel@lists.infradead.org Cc: Catalin Marinas , Will Deacon , Ryan Roberts , Mark Rutland , Lorenzo Stoakes , Andrew Morton , Mike Rapoport , Linu Cherian , linux-kernel@vger.kernel.org, linux-mm@kvack.org, kasan-dev@googlegroups.com References: <20260224051153.3150613-1-anshuman.khandual@arm.com> <20260224051153.3150613-8-anshuman.khandual@arm.com> <238ab437-06b1-43ef-86bb-9341c02040b1@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260415_033515_354226_148A8D21 X-CRM114-Status: GOOD ( 10.39 ) X-BeenThere: linux-arm-kernel@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-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org >>> >>> @@ -2258,4 +2258,21 @@ int pmdp_test_and_clear_young(struct vm_area_struct *vma, >>> } >>> #endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG */ >>> >>> +#if CONFIG_PGTABLE_LEVELS > 3 >>> +phys_addr_t pud_offset_phys(p4d_t *p4dp, unsigned long addr) >>> +{ >>> + p4d_t p4d = p4dp_get(p4dp); >>> + >>> + BUG_ON(!pgtable_l4_enabled()); >> >> Heh, while at it, convert that to a VM_WARN_ON_ONCE() or anything else >> that is not a BUG. >> >> I strongly assume CONFIG_DEBUG_VM checks are sufficient. > > There are multiple similar BUG_ON() instances > > arch/arm64/include/asm/pgtable.h: BUG_ON(!pgtable_l4_enabled()); > arch/arm64/include/asm/pgtable.h: BUG_ON(!pgtable_l5_enabled()); > > arch/arm64/mm/mmu.c: BUG_ON(pmd_val(old_pmd) != 0 && > arch/arm64/mm/mmu.c: BUG_ON(pud_val(old_pud) != 0 && > arch/arm64/mm/mmu.c: BUG_ON(p4d_val(old_p4d) != 0 && > > Shall we convert all of them as VM_WARN_ON_ONCE() in a separate patch > as a pre-requisite ? In MM at least, we fix them up when touching the code, and only sometimes convert entire files. As documented in Documentation/process/coding-style.rst, there might be some exceptions where BUG_ON makes sense (severe data corruption possible), and some cases would want to use WARN_ON_ONCE() + recovery code. All of these cases here sound like VM_WARN_ON_ONCE() is more than sufficient though, so feel free to convert them all in one shot. -- Cheers, David