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[209.132.180.67]) by mx.google.com with ESMTP id d128-v6si207656pfc.211.2018.09.04.16.37.26; Tue, 04 Sep 2018 16:37:43 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725900AbeIEEDi (ORCPT + 99 others); Wed, 5 Sep 2018 00:03:38 -0400 Received: from smtp.eu.citrix.com ([185.25.65.24]:12315 "EHLO SMTP.EU.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725726AbeIEEDh (ORCPT ); Wed, 5 Sep 2018 00:03:37 -0400 X-IronPort-AV: E=Sophos;i="5.53,330,1531785600"; d="scan'208";a="78551621" Subject: Re: [Xen-devel] [PATCH] xen-swiotlb: use actually allocated size on check physical contiguous To: Dongli Zhang , "xen-devel@lists.xenproject.org" CC: John Sobecki , Joe Jin , "linux-kernel@vger.kernel.org" , References: From: Andrew Cooper Openpgp: preference=signencrypt Autocrypt: addr=andrew.cooper3@citrix.com; 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Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit Content-Language: en-GB X-ClientProxiedBy: AMSPEX02CAS02.citrite.net (10.69.22.113) To AMSPEX02CL02.citrite.net (10.69.22.126) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/09/18 00:14, Dongli Zhang wrote: > Below module would help people reproduce the issue to understand the symptom: > > https://github.com/finallyjustice/patchset/blob/master/xen-swiotlb-panic.c > > In addition, on the xen hypervisor side, the memory_exchange() in xen hypervisor > does not check if the the pfn of input mfn belong to the same extent are > continuous in guest domain. As a result, the wrong page is stolen from guest domain. > > Can we assume it is fine to not check if pfn of mfn are continuous in xen > hypervisor? The purpose of the memory_exchange hypercall is to exchange any arbitrary set of guest frames with an equivalently sized set frames with different properties. The practical use is for PV guests to be able to create a DMA buffer which is physically continuous.  Xen does not, and indeed should not, care about the properties of the input frame list. ~Andrew