From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 12120D6AB13 for ; Thu, 2 Apr 2026 20:44:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=XtVsTEkrUECjJRD7aGi/0e7Hl5IiiR2QyYRJQgcmHRU=; b=QXgHqtKXrY1dIGkw71GsKFIFw9 gr1ieReLlReMWBuzRhVyzf62XVxXTfcCceGJFaazvfDCbzFagcGkYTH07OzEuuTU2rEIGzkKDe84z vxboQjV6aXfdqTEFueEcdYOhxVabPldg2gb7CMSgd0M7JWly3REsQaWexAVJJzkzdqu41R9exEO4I q783yxU3m3OJt3QR05b+Gc3awLOppEOFdxczR0qeFpjUhlwEkIsqe/ilCI5ZhU1Pq/gxmbIdg0Adb ZfGeEDomBmlHx2uQQ0wHkTft+6z2aA3+EBs8cCt0mBSlGjQfYtzWKO8nlaGPY1h0FxSF3HF8AxBaH Sg38EvsQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1w8Otf-00000000lTb-0ssP; Thu, 02 Apr 2026 20:44:11 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1w8Otb-00000000lT9-3oL3 for linux-arm-kernel@lists.infradead.org; Thu, 02 Apr 2026 20:44:09 +0000 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260330161705.3349825-2-ryan.roberts@arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260402_134408_159950_97FEBD1E X-CRM114-Status: GOOD ( 27.76 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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