From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id F20772E2665; Thu, 2 Apr 2026 20:44:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775162647; cv=none; b=O7tftvEa7Ynj6Vv8IKAZeBwFS5zAiUNPbJnUI6x9p89rvqbfSBMuWTCpYP/HRKM6bWldFtrg1mSNwCELNdIOEj+V0Gp+MDfG4BfHgs1bkajWUdbp9voA4EEsTPHAEsQW9ZTxDmq8YiUY6dPoDXcyYz5dfWYzi+rU1OSeH4VplkU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775162647; c=relaxed/simple; bh=cjEZkKQ+ODVU3DKbmEDkBuKAPPbwImPNm5BnHCLYCdA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=mvFSkT/a8h6gPW62H/uDEcF47aGO6qHf5oanUDZAADw3scAQSznEiwSyvckDy7RV6+wDBGI8ZfwHRg9CCT3kymw3eAaCimZrD9SH2RSvBxbrtZXCHXUyysqRDmAlymf9PWt3GZ+3E+rPgTcV95pDerGfOO5V4aHqyDmlnfLgrbk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=rMISpFzg; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="rMISpFzg" 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 192EA176B; Thu, 2 Apr 2026 13:43:58 -0700 (PDT) Received: from arm.com (usa-sjc-mx-foss1.foss.arm.com [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 3ED233F915; Thu, 2 Apr 2026 13:44:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1775162643; bh=cjEZkKQ+ODVU3DKbmEDkBuKAPPbwImPNm5BnHCLYCdA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=rMISpFzgJPXbGvKghDviAPSjcuME2BDYXFgSL9AnIbxA4cAcDMShJErC2ayBI5Wdz 4AXjfquKWnELfq3rw5MB99YKMgHGZNzxLt9DFqQHuEXzExkBF9z5zR0fl/jfkORk1r 1hkhnj8rf6S/kx7qKb9lbVJe0u0k8T0CUysryFhI= Date: Thu, 2 Apr 2026 21:43:59 +0100 From: Catalin Marinas To: Ryan Roberts Cc: Will Deacon , "David Hildenbrand (Arm)" , Dev Jain , Yang Shi , Suzuki K Poulose , Jinjiang Tu , Kevin Brodsky , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH v2 1/3] arm64: mm: Fix rodata=full block mapping support for realm guests Message-ID: References: <20260330161705.3349825-1-ryan.roberts@arm.com> <20260330161705.3349825-2-ryan.roberts@arm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260330161705.3349825-2-ryan.roberts@arm.com> On Mon, Mar 30, 2026 at 05:17:02PM +0100, Ryan Roberts wrote: > int split_kernel_leaf_mapping(unsigned long start, unsigned long end) > { > int ret; > > - /* > - * !BBML2_NOABORT systems should not be trying to change permissions on > - * anything that is not pte-mapped in the first place. Just return early > - * and let the permission change code raise a warning if not already > - * pte-mapped. > - */ > - if (!system_supports_bbml2_noabort()) > - return 0; > - > /* > * If the region is within a pte-mapped area, there is no need to try to > * split. Additionally, CONFIG_DEBUG_PAGEALLOC and CONFIG_KFENCE may > * change permissions from atomic context so for those cases (which are > * always pte-mapped), we must not go any further because taking the > - * mutex below may sleep. > + * mutex below may sleep. Do not call force_pte_mapping() here because > + * it could return a confusing result if called from a secondary cpu > + * prior to finalizing caps. Instead, linear_map_requires_bbml2 gives us > + * what we need. > */ > - if (force_pte_mapping() || is_kfence_address((void *)start)) > + if (!linear_map_requires_bbml2 || is_kfence_address((void *)start)) > return 0; > > + if (!system_supports_bbml2_noabort()) { > + /* > + * !BBML2_NOABORT systems should not be trying to change > + * permissions on anything that is not pte-mapped in the first > + * place. Just return early and let the permission change code > + * raise a warning if not already pte-mapped. > + */ > + if (system_capabilities_finalized()) > + return 0; > + > + /* > + * Boot-time: split_kernel_leaf_mapping_locked() allocates from > + * page allocator. Can't split until it's available. > + */ > + if (WARN_ON(!page_alloc_available)) > + return -EBUSY; > + > + /* > + * Boot-time: Started secondary cpus but don't know if they > + * support BBML2_NOABORT yet. Can't allow splitting in this > + * window in case they don't. > + */ > + if (WARN_ON(num_online_cpus() > 1)) > + return -EBUSY; > + } I think sashiko is over cautions here (https://sashiko.dev/#/patchset/20260330161705.3349825-1-ryan.roberts@arm.com) but it has a somewhat valid point from the perspective of num_online_cpus() semantics. We have have num_online_cpus() == 1 while having a secondary CPU just booted and with its MMU enabled. I don't think we can have any asynchronous tasks running at that point to trigger a spit though. Even async_init() is called after smp_init(). An option may be to attempt cpus_read_trylock() as this lock is taken by _cpu_up(). If it fails, return -EBUSY, otherwise check num_online_cpus() and unlock (and return -EBUSY if secondaries already started). Another thing I couldn't get my head around - IIUC is_realm_world() won't return true for map_mem() yet (if in a realm). Can we have realms on hardware that does not support BBML2_NOABORT? We may not have configuration with rodata_full set (it should be complementary to realm support). I'll add the patches to for-next/core to give them a bit of time in -next but let's see next week if we ignore this (with an updated comment) or we try to avoid the issue altogether. -- Catalin