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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D5DB3C433F5 for ; Wed, 10 Nov 2021 20:56:27 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 8F583611F2 for ; Wed, 10 Nov 2021 20:56:27 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 8F583611F2 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=lists.xenproject.org Received: from list by lists.xenproject.org with outflank-mailman.224461.387739 (Exim 4.92) (envelope-from ) id 1mkudW-0004Qd-Tu; Wed, 10 Nov 2021 20:56:02 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 224461.387739; Wed, 10 Nov 2021 20:56:02 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1mkudW-0004QW-Qn; Wed, 10 Nov 2021 20:56:02 +0000 Received: by outflank-mailman (input) for mailman id 224461; Wed, 10 Nov 2021 20:56:01 +0000 Received: from se1-gles-sth1-in.inumbo.com ([159.253.27.254] helo=se1-gles-sth1.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1mkudV-0004QQ-J3 for xen-devel@lists.xenproject.org; Wed, 10 Nov 2021 20:56:01 +0000 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by se1-gles-sth1.inumbo.com (Halon) with ESMTPS id 9abed4ea-4268-11ec-9787-a32c541c8605; Wed, 10 Nov 2021 21:55:59 +0100 (CET) Received: by mail.kernel.org (Postfix) with ESMTPSA id 7722660F9E; Wed, 10 Nov 2021 20:55:57 +0000 (UTC) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: 9abed4ea-4268-11ec-9787-a32c541c8605 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1636577757; bh=QG21js8um63uDNzMq78czGQSSHxcpPkPxozWL0pwq90=; h=From:To:Cc:Subject:Date:From; b=TnHG4meTexFAOJHdh86b/sUsOz2BF863LPizP6RLwgQ4I8EAcLWv9jh02UTQOPvR9 eURfL92JfpRp8sjqV9bEMDGrUxlKZSUL7sS9BuCGk0V2OWOeJagBqOh7DpamhjJNiT UGjqoWAnmLGJXh1QeCKS/xYNVxzi1pv4LheNUv56UILFivQPoxMwRPu5+2Z6BGqJrs 7NIsOiUJgXZCwv2ZqZv9n57vtoEC67bcF/e0MHTzABEzGzkz5QnNpe9yrCkRpgqIih cLnuSoXUJR3AG9iifwjWGeAXrjSensElStK3O3jjX8lAo+C35kfmhG/eMVZhR/mf3b 5G8/RrapmWOMg== From: Stefano Stabellini To: julien@xen.org Cc: sstabellini@kernel.org, xen-devel@lists.xenproject.org, oleksandr_tyshchenko@epam.com, iwj@xenproject.org, Bertrand.Marquis@arm.com, Volodymyr_Babchuk@epam.com, Stefano Stabellini Subject: [PATCH v2 for-4.16] xen/arm: allocate_bank_memory: don't create memory banks of size zero Date: Wed, 10 Nov 2021 12:55:55 -0800 Message-Id: <20211110205555.945026-1-sstabellini@kernel.org> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Stefano Stabellini allocate_bank_memory can be called with a tot_size of zero, as an example see the implementation of allocate_memory which can call allocate_bank_memory with a tot_size of zero for the second memory bank. If tot_size == 0, don't create an empty memory bank, just return immediately without error. Otherwise a zero-size memory bank will be added to the domain device tree. Note that Linux is known to be able to cope with zero-size memory banks, and Xen more recently gained the ability to do so as well (5a37207df520 "xen/arm: bootfdt: Ignore empty memory bank"). However, there might be other non-Linux OSes that are not able to cope with empty memory banks as well as Linux (and now Xen). It would be more robust to avoid zero-size memory banks unless required. Moreover, the code to find empty address regions in make_hypervisor_node in Xen is not able to cope with empty memory banks today and would result in a Xen crash. This is only a latent bug because make_hypervisor_node is only called for Dom0 at present and allocate_memory is only called for DomU at the moment. (But if make_hypervisor_node was to be called for a DomU, then the Xen crash would become manifest.) Fixes: f2931b4233ec ("xen/arm: introduce allocate_memory") Signed-off-by: Stefano Stabellini --- Changes in v2: - improve commit message - add in-code comment In regards to inclusion in 4.16. If we don't fix this issue in 4.16, default usage of Xen+Linux won't be affected. However: - Non-Linux OSes that cannot cope with zero-size memory banks could error out. I am not aware of any but there are so many out there in embedded it is impossible to tell. - downstream Xen calling make_hypervisor_node for DomUs will crash - future Xen calling make_hypervisor_node for DomUs will have to make sure to fix this anyway If we commit the patch in 4.16, we fix these issue. This patch is only 2 lines of code and very easy to review. The risk is extremely low. Difficult to say what mistakes could have been made in analysis and preparation because it is a trivial if-zero-return patch, which is likely to fix latent bugs rather than introducing instability. --- xen/arch/arm/domain_build.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c index 9e92b640cd..fe38a7c73c 100644 --- a/xen/arch/arm/domain_build.c +++ b/xen/arch/arm/domain_build.c @@ -395,6 +395,14 @@ static bool __init allocate_bank_memory(struct domain *d, struct membank *bank; unsigned int max_order = ~0; + /* + * allocate_bank_memory can be called with a tot_size of zero for + * the second memory bank. It is not an error and we can safely + * avoid creating a zero-size memory bank. + */ + if ( tot_size == 0 ) + return true; + bank = &kinfo->mem.bank[kinfo->mem.nr_banks]; bank->start = gfn_to_gaddr(sgfn); bank->size = tot_size; -- 2.25.1