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 7360733B6C6; Tue, 7 Apr 2026 17:21:58 +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=1775582521; cv=none; b=OJfKOaIllWNTwVW9oH5kqpqa+Hz6RTPBMFSyLYCH7gjq8vo4ZjVoQxnxCQ/a7k//h0Ek2OQTJ3ubJrkVthtcw69g/JOPqJ5FdVd5cFi/+zhPTNfYnciJA8UCHy6nb/WcuqdVMg5HeLwI5bj0K9gBlHX+NJ+bTTjug8RUNwiqGbk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775582521; c=relaxed/simple; bh=vE/AzNTfxAsg7nwOsnitaQKhZsQBUYcc/ffth8fx+bc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ArT1+4PKMbMhbXRonlblFtip57hrYQ0UEHM2LJMbK2szv1zMJxZPeeMjDfHQ1RRoKNqmlJXRQvvBh6jqiqJ5qPd9YfQnQLS1sFHn0DLqJenPdqBUF+79cC22rShLegE34KV8OgkgDKE/O3UQB3hgqYBnmS7YK1fdpctSH43g2dQ= 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=h7Z3X3BK; 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="h7Z3X3BK" 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 216B032E3; Tue, 7 Apr 2026 10:21:46 -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 1D52E3F7D8; Tue, 7 Apr 2026 10:21:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1775582511; bh=vE/AzNTfxAsg7nwOsnitaQKhZsQBUYcc/ffth8fx+bc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=h7Z3X3BK/362O7Vz9OIZI86q27eRa/LA1xc0dXRnrXZUnIpaHf0rKSF7N80DEBhWO AGzbcJ48pRiJUqTA+qqJHR05e1ozCHdLAuAUdJ4i+s13fq0yXHT+eAP1EhBD2Wd1vh 31Ycs7Bp/OQ/017uELGc0nViD+mDktdsld9TwgKM= Date: Tue, 7 Apr 2026 18:21:47 +0100 From: Catalin Marinas To: Suzuki K Poulose Cc: Ryan Roberts , Will Deacon , "David Hildenbrand (Arm)" , Dev Jain , Yang Shi , 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> <1db93bd3-cb47-445b-b8ca-6de6f04b41cc@arm.com> Precedence: bulk X-Mailing-List: stable@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: <1db93bd3-cb47-445b-b8ca-6de6f04b41cc@arm.com> On Tue, Apr 07, 2026 at 10:57:35AM +0100, Suzuki K Poulose wrote: > On 02/04/2026 21:43, Catalin Marinas wrote: > > 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). > > That is correct. map_mem() comes from paginig_init(), which gets called > before arm64_rsi_init(). Realm check was delayed until psci_xx_init(). > We had a version which parsed the DT for PSCI conduit early enough > to be able to make the SMC calls to detect the Realm. But there > were concerns around it. Ah, yes, I remember. Does it mean that commit 42be24a4178f ("arm64: Enable memory encrypt for Realms") was broken without rodata=full w.r.t. the linear map? Commit a166563e7ec3 ("arm64: mm: support large block mapping when rodata=full") introduced force_pte_mapping() but it just copied the logic in the existing can_set_direct_map(). Looking at the linear_map_requires_bbml2 assignment, we get (!is_realm_world() && is_realm_world()) and it cancels out, no effect on it but we don't get pte mappings either (even if we don't have BBML2). I think we need at least some safety checks: 1. BBML2_NOABORT support on the boot CPU - continue with the existing logic (as per Ryan's series) 2. !system_supports_bbml2_noabort() - split in linear_map_maybe_split_to_ptes(). This does not currently happen because linear_map_requires_bbml2 may be false in the absence of rodata=full. Not sure how to fix this without some variable telling us how the linear map was mapped. The requires_bbml2 flag doesn't 3. Panic in arm64_rsi_init() if !BBML2_NOABORT on the boot CPU _and_ we have block mappings already. People can avoid it with rodata=full 4. If (3) is a common case, a better alternative is to rewrite the linear map sometime after arm64_rsi_init() but before we call split_kernel_leaf_mapping(). -- Catalin