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 1B110CAC58D for ; Thu, 11 Sep 2025 09:10:23 +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=2OQfaMO63VuoxYCGwCbKDFCxYqnQrnEU0U6YCwkAda8=; b=FJJOO2v99LYH4x9gd02Q/klf3v 3TWmGNBYRzFceaO8NOGIOiyIqle1wLQLQaLrDfzbXRD2lvmG8+fRJrJY4vT3ij+GRpg0uHCGwHOzN F51G43/nzaYCiXzZLHEaLtFAizP3e2aR56//kpycHK+3XHYZcniCTiiBDWKQlqzr64VJ7cFic3t24 nwR51QDahoUXF4OHUdgHowocpf3TevehOyXMInEynTG2bI0NeiCacX8JBIyH9xQ7RmmiddX5nC9IC WSXphwe3mZ2R+FnXWMRhbMWVfSOo2wODSr/KYHN8EpeHaPVeu3aBN5J1EC/d+FMktrXawWWPH4awl 089vAjDw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1uwdJp-000000021ZM-0SNp; Thu, 11 Sep 2025 09:10:17 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1uwdJm-000000021YD-2uTB for linux-arm-kernel@lists.infradead.org; Thu, 11 Sep 2025 09:10:16 +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 38ED9153B; Thu, 11 Sep 2025 02:10:05 -0700 (PDT) Received: from [10.57.70.14] (unknown [10.57.70.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 457633F694; Thu, 11 Sep 2025 02:10:11 -0700 (PDT) Message-ID: Date: Thu, 11 Sep 2025 11:10:09 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] arm64: mm: Move KPTI helpers to mmu.c To: Ard Biesheuvel , Anshuman Khandual Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Catalin Marinas , Kees Cook , Mark Rutland , Ryan Roberts , Suzuki K Poulose , Will Deacon , Yeoreum Yun References: <20250910104454.317067-1-kevin.brodsky@arm.com> <41f3227e-b945-4303-90b7-732affb0a101@arm.com> Content-Language: en-GB From: Kevin Brodsky In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250911_021014_857316_AC58CAD8 X-CRM114-Status: GOOD ( 15.74 ) 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 On 11/09/2025 08:24, Ard Biesheuvel wrote: > On Thu, 11 Sept 2025 at 08:18, Anshuman Khandual > wrote: >> >> >> On 11/09/25 11:38 AM, Ard Biesheuvel wrote: >>> On Thu, 11 Sept 2025 at 07:13, Anshuman Khandual >>> wrote: >>>> >>>> >>>> On 10/09/25 4:14 PM, Kevin Brodsky wrote: >>>>> create_kpti_ng_temp_pgd() is currently defined (as an alias) in >>>>> mmu.c without matching declaration in a header; instead cpufeature.c >>>>> makes its own declaration. This is clearly not pretty, and as commit >>>>> ceca927c86e6 ("arm64: mm: Fix CFI failure due to kpti_ng_pgd_alloc >>>>> function signature") showed, it also makes it very easy for the >>>>> prototypes to go out of sync. >>>>> >>>>> All this would be much simpler if kpti_install_ng_mappings() and >>>>> associated functions lived in mmu.c, where they logically belong. >>>>> This is what this patch does: >>>>> - Move kpti_install_ng_mappings() and associated functions from >>>>> cpufeature.c to mmu.c, add a declaration to >>>>> - Make create_kpti_ng_temp_pgd() a static function that simply calls >>>>> __create_pgd_mapping_locked() instead of aliasing it >>>>> - Mark all these functions __init >>>>> - Move __initdata after kpti_ng_temp_alloc (as suggested by >>>>> checkpatch) >>>>> >>>>> Signed-off-by: Kevin Brodsky >>>>> --- >>>>> Note: as things stand, create_kpti_ng_temp_pgd() could be removed, >>>>> but a separate patch [1] will make use of it to add an >>>>> assertion. >>>>> >>>>> [1] https://lore.kernel.org/all/20250813145607.1612234-3-chaitanyas.prakash@arm.com/ >>>>> --- >>>>> Cc: Anshuman Khandual >>>>> Cc: Ard Biesheuvel >>>>> Cc: Catalin Marinas >>>>> Cc: Kees Cook , >>>>> Cc: Mark Rutland >>>>> Cc: Ryan Roberts >>>>> Cc: Suzuki K Poulose >>>>> Cc: Will Deacon >>>>> Cc: Yeoreum Yun >>>>> --- >>>>> arch/arm64/include/asm/mmu.h | 6 ++ >>>>> arch/arm64/kernel/cpufeature.c | 97 ------------------------------ >>>>> arch/arm64/mm/mmu.c | 106 ++++++++++++++++++++++++++++++--- >>>>> 3 files changed, 103 insertions(+), 106 deletions(-) >>>>> >>>>> diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h >>>>> index 49f1a810df16..624edd6c4964 100644 >>>>> --- a/arch/arm64/include/asm/mmu.h >>>>> +++ b/arch/arm64/include/asm/mmu.h >>>>> @@ -104,5 +104,11 @@ static inline bool kaslr_requires_kpti(void) >>>>> return true; >>>>> } >>>>> >>>>> +#ifdef CONFIG_UNMAP_KERNEL_AT_EL0 >>>>> +void kpti_install_ng_mappings(void); >>>> Could the declarations be moved here instead ? >>> Why? >> To avoid both typedef and external instance declaration in the C >> code even though there is just a single call site in there. > But why would we want to avoid those in the first place? > > Moving these into mmu.h pollutes the global namespace with > declarations that must never be used outside of > __kpti_install_ng_mappings() to begin with. That makes sense to me - no need for these declarations to be in a header as they're implementation details of __kpti_install_ng_mappings(). What is more common is to have them at the top-level in the .c file instead of inside a function, but I think either way is fine. - Kevin