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 X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1299AC433DF for ; Tue, 26 May 2020 07:41:47 +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 CFA732070A for ; Tue, 26 May 2020 07:41:46 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CFA732070A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jdUD7-0001j3-C1; Tue, 26 May 2020 07:41:17 +0000 Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jdUD6-0001iy-M7 for xen-devel@lists.xenproject.org; Tue, 26 May 2020 07:41:16 +0000 X-Inumbo-ID: 476dc06c-9f24-11ea-af7d-12813bfff9fa Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id 476dc06c-9f24-11ea-af7d-12813bfff9fa; Tue, 26 May 2020 07:41:15 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id AA006B029; Tue, 26 May 2020 07:41:17 +0000 (UTC) Subject: Re: Bug: toolstack allows too low values to be set for shadow_memory To: Hans van Kranenburg References: <37137142-1e34-0f78-c950-91bcd6543eb8@knorrie.org> From: Jan Beulich Message-ID: <304a7a55-20a6-1dfe-1f3a-dabe90d28f40@suse.com> Date: Tue, 26 May 2020 09:41:08 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <37137142-1e34-0f78-c950-91bcd6543eb8@knorrie.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: "xen-devel@lists.xenproject.org" Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" On 25.05.2020 17:51, Hans van Kranenburg wrote: > This bug report is a follow-up to the thread "Domu windows 2012 crash" > on the xen-users list. In there we found out that it is possible to set > a value for shadow_memory that is lower than a safe minimum value. > > This became apparent after XSA-304, which caused using more of this type > of memory. Having a hardcoded line like shadow_memory = 8 results in > random crashes of the guest, I don't think it is the tool stack's responsibility to override admin requested values, or at least not as far a affecting guest stability goes; host stability of course needs to be guaranteed, but that's then still the hypervisor's job, not the tool stack's. Compare this to e.g. setting too small a memory= for a guest to be able to boot at all, or setting maxmem > memory for a guest without balloon driver. Furthermore - what would the suggestion be as to a "safe minimum value"? Assuming _all_ large pages may potentially get shattered is surely a waste of memory, unless the admin really knows guests are going to behave that way. (In your report you also didn't mention what memory= values the issue was observed with. Obviously larger memory= also require bumping shadow_memory= at least from some point onwards.) Jan