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 C2FBC35A387; Thu, 9 Apr 2026 09:38:07 +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=1775727493; cv=none; b=Y6VpnmiAJsqoSH1WjF2zxGM6KUSwG3WhEMwJEiyVf+Qf3xg/qVOeXABk1MmuRx+OgR9hR4cwwbrRZwmIURyS2cdGZ4FJ90Km3izMtIWt3+eKL9R2I1xAPniFp3hyLjXpQoNMnT80AkKdQB01TRT3kJwts8qnQ/krN6dWb4ZtuPU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775727493; c=relaxed/simple; bh=hgmnPKQeJdguRlzqCxqX311nWdNqYCRj8dOAtXBPPzw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=BBY41CjkGm6PvsOgNkqqGRLfwxo3AD3+u6B3Tuz2yBx3YlwjdBHmUP4AWq+y2ibi5j3Lg9VxSVkXJ53EwpHRffVCFy+L4j00lnHo2rUrtb4GTqINnCVIMaOxWCiFHQJ5aT6aTlW4P/L9i4PHUQEnroWsPGpFYm06om+6gW0ErkU= 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=hC/IvXMS; 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="hC/IvXMS" 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 141813561; Thu, 9 Apr 2026 02:38:01 -0700 (PDT) Received: from [10.57.62.20] (unknown [10.57.62.20]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 63D833F641; Thu, 9 Apr 2026 02:38:05 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1775727486; bh=hgmnPKQeJdguRlzqCxqX311nWdNqYCRj8dOAtXBPPzw=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=hC/IvXMS8TJYS+ZWAlgtGthk/NXbUKaJl/BHJKb0sN78HuIrXfz5kLE6MTDTAlHLH 6CfRBzNFwh+7vksFuaerj4PNEU7FXahuGZImTHrVJl7s8vasz3GOIFGZWLxVp5dE2h ARuPsj61IbfCGD+1Z9HcmG2GwWR3rZfJp5W3Hiis= Message-ID: Date: Thu, 9 Apr 2026 10:38:03 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/3] arm64: mm: Fix rodata=full block mapping support for realm guests Content-Language: en-GB To: Catalin Marinas 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 References: <20260330161705.3349825-1-ryan.roberts@arm.com> <20260330161705.3349825-2-ryan.roberts@arm.com> <1db93bd3-cb47-445b-b8ca-6de6f04b41cc@arm.com> From: Suzuki K Poulose In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 07/04/2026 18:21, Catalin Marinas wrote: > 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 Apparently, it looks like we missed this when we demoted the RSI detection later. > 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). Yep, that's right. > > 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 It looks like this will be a common case :-( > > 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(). We will explore this route. The other option is to move the RSI detection (and the PSCI probe) earlier to be able to make better decisions early on. I will play with that a bit too. Suzuki >