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 B4E5B3CC310 for ; Thu, 11 Jun 2026 11:14:37 +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=1781176479; cv=none; b=Z78rlsG+S7g0zOJU+Py3ep87siHhWtKmZAARLjvv1UMBTIT40R6nxonpo4Z1ObfBz/9MA/reWTQmjYJE59wxQyvualJSXyMAJR/+LHCBZHvCS4HBKCc1akxMynPUgy0nUJGoDnBlHSr575NDIaFuzqpsFLXWb3DdZBK6SZcW3Tk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781176479; c=relaxed/simple; bh=jqEfeaKy1cws55DOS6rs5gSZGwNp6LsQg+WD+PXBkJs=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=j8YcvlU/2Y3Zr4FK8rUdsaVY6EHDnZGffZH0nRrbV9vCayeYLELIz5GIUS+LPoUDHlU1nHpxnmIlqPARtQRLROWE96Kn7Pt7hAeCoOzkOfKZ5CdWpSbAN1DTEoLoBvqkSuJH+6NurC5511SaTTcmU/HCWtPiQgOptKZEVFzFAf4= 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=TQeQ+fOf; 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="TQeQ+fOf" 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 1480B1E2F; Thu, 11 Jun 2026 04:14:32 -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 57C703F99C; Thu, 11 Jun 2026 04:14:35 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1781176476; bh=jqEfeaKy1cws55DOS6rs5gSZGwNp6LsQg+WD+PXBkJs=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=TQeQ+fOfyqgZQB8FuaD041IjUolkuGWu3iBJY2dW8RjzzTTQYETBuku+5y6qBaCe4 S5zJtY3owR7uMiZOyQS/A0wTKqNvRDNbBIln9itzMah2vhtdwfdXmCWhIQTaZAmf7l 0fByKbyr+wSnvjWxWSLys/p9EqCD4HlCM7YPwUnA= Date: Thu, 11 Jun 2026 12:14:28 +0100 From: Catalin Marinas To: Suzuki K Poulose Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, will@kernel.org, ardb@kernel.org, lpieralisi@kernel.org, mark.rutland@arm.com, steven.price@arm.com, aneesh.kumar@kernel.org, sudeep.holla@arm.com, robh@kernel.org, maz@kernel.org Subject: Re: [RFC PATCH v2 0/4] arm64: realm: Support for probing RSI earlier Message-ID: References: <20260505155742.623287-1-suzuki.poulose@arm.com> <470678cb-b8b0-4b09-bf32-97fb037ed849@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: <470678cb-b8b0-4b09-bf32-97fb037ed849@arm.com> On Fri, May 29, 2026 at 01:27:01PM +0100, Suzuki K Poulose wrote: > On 28/05/2026 17:06, Catalin Marinas wrote: > > On Tue, May 05, 2026 at 04:57:38PM +0100, Suzuki K Poulose wrote: > > > This is an updated series, addressing the review comments from AI agent on > > > the version 1 [0] of the series, (some of which were documented as short comings). > > > See below for the changes. > > > > > > The Realm Guest linux support is broken without rodata=full (fortunately default > > > for arm64), as we detect the RSI support after we have created the Linear map > > > with Block/Contiguous mappings. If the boot CPU doesn't support BBML2_NOABORT > > > (there are CPUs out there with FEAT_RME and no - useable - BBML2_NOABORT) > > > we are then not able to split the page tables down to PTE level if the system > > > as such doesn't support BBML2. > > > > > > See the following link for the discussion. > > > > > > https://lore.kernel.org/all/20260330161705.3349825-2-ryan.roberts@arm.com/ > > > > > > The available options are : > > > 1. Start with PTE level mappings at paging_init() and then "FOLD" the page tables > > > to Block/Cont mappings after we have the full picture available. Looking at the > > > future (with BBML3), this might mean "additional work" for most of the systems > > > at boot. But not bad as splitting them ? > > > 2. Hold the secondary CPUs in busy loop with MMU disabled and split the mappings > > > by the boot CPU with MMU off (if Boot CPU can't support BBML2). This is tricky > > > with the page allocations required to add the page-tables. > > > 3. Move the detection of Realm support earlier to make a better decision for > > > paging_init(), with an added bonus of earlycon support for Realms without > > > the user having to work out the "top bit" for the Realm. > > > > > > This series is an attempt to implement (3) (without the earlycon support). We try > > > to probe the PSCI conduit early from the DT/ACPI. DT is not flattened at this time. [...] > > Could we instead add a more informative message in arm64_rsi_init() if > > !force_pte_mappings() && !cpu_supports_bbml2_noabort() (before > > is_realm_world() becomes true)? Well, it may not print anything if the > > early console is not set up yet. > > That is true, but with some expertise you may be able to enable earlycon > and may be we could get some new mechanism for "earlycon" for Realms. > > The other way to look at is: > > When the system doesn't support BBML2 Abort: > > Creating block/Cont mappings to start with and then splitting it to PTE > is quite difficult as we : > 1. Need to allocate pages for leaf level tables > 2. Hold the other CPUs in tight loop Agree, that's not easily possible at runtime. > Instead, creating the block/CONT levels from a fully "page level" > mappings are easier, as we can: > > 1. Can easily fold the tables to Block mapping with reclaiming the leaf > level pagetables. > > 2. Avoid the secondary CPUs dance, as they all support BBML2_NOABORT. > > This shouldn't be that bad as the opposite ? I don't think it solves our problem. Aren't we concerned with the rodata=off && !BBML2_NOABORT && is_realm_world() case? I don't think your second point stands. Currently we have: rodata=full && BBML2_NOABORT => block mappings irrespective of realms rodata=off && BBML2_NOABORT => block mappings first, can be split later if is_realm_world() rodata=off && !BBML2_NOABORT => block mappings first, serious problem if is_realm_world() It's the last case we need to fix. Starting with page mappings does avoid the in-realm failure but the !is_realm_world() case folding to block mappings still requires proper BBM. -- Catalin