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 021C42ED141; Tue, 7 Apr 2026 09:57:38 +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=1775555860; cv=none; b=TOSuyPrX/o+eFkrxhctuLUbJeJk6QWJDjzve0o/w86stP6fccyg90ND/KoB1lZthSXFixx4g7fsL9M4m3lWY/mZvrC9kGYmZ/lKG8ib2uRcx7eE3I9Mmn1Lp1ESzHwHqS94SuHy2v+hVOfYFWiO8VSTzIK6vz/4z+98HqFu0Ro0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775555860; c=relaxed/simple; bh=GDEYdp9RtUTCRAaXXYD6KpDKVf+j1vyiOvYCN2p8fxE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=BvD2aTQFQ1QAAD6LyqsfTMcfzGKfEjaRUeCMjA4TW37G1cnEQRdMX1Px5JC4pUaPrySO7tolhAqTqI0NFoTeX5D7iuXJ0CDkyO6q4wai+3CrbEjzZDsdOepaJvSPFzvLlDKpt7lSxuM/vifXPKNJxn3vO0KBHBRtr+CahpCOBnM= 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=XU+r8HEd; 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="XU+r8HEd" 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 A354D1BB2; Tue, 7 Apr 2026 02:57:32 -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 C21E03F7D8; Tue, 7 Apr 2026 02:57:36 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1775555858; bh=GDEYdp9RtUTCRAaXXYD6KpDKVf+j1vyiOvYCN2p8fxE=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=XU+r8HEdffWkHWIz9LDQmKaOh8jWEiuN53Vb72TAtJ3qBPJmaTUn5V/Ts74qgohF5 ZiYUKRdqLa89HvI499eDJOJgZprE6LBFrCyNrR87yMTQ0mZowKa7ZQWUaQGHnF5TLK fEsXI26cKPemRpcd0cCuCQ3rXNI/1DUSJahoD9vY= Message-ID: <1db93bd3-cb47-445b-b8ca-6de6f04b41cc@arm.com> Date: Tue, 7 Apr 2026 10:57:35 +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 , Ryan Roberts Cc: 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> From: Suzuki K Poulose In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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. > Can we have realms on hardware that does not support BBML2_NOABORT? I can get this checked. I expect that they all will have BBML2 (v8.4 extension). But NOABORT is something that may need to be checked. 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. > Thanks Suzuki