From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e23smtp07.au.ibm.com (e23smtp07.au.ibm.com [202.81.31.140]) (using TLSv1.2 with cipher CAMELLIA256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3qQlS10N5VzDq6T for ; Thu, 17 Mar 2016 21:47:45 +1100 (AEDT) Received: from localhost by e23smtp07.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 17 Mar 2016 20:47:43 +1000 Received: from d23relay10.au.ibm.com (d23relay10.au.ibm.com [9.190.26.77]) by d23dlp02.au.ibm.com (Postfix) with ESMTP id 6F36B2BB0054 for ; Thu, 17 Mar 2016 21:47:34 +1100 (EST) Received: from d23av04.au.ibm.com (d23av04.au.ibm.com [9.190.235.139]) by d23relay10.au.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id u2HAlQhH19792026 for ; Thu, 17 Mar 2016 21:47:34 +1100 Received: from d23av04.au.ibm.com (localhost [127.0.0.1]) by d23av04.au.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id u2HAl0nH012274 for ; Thu, 17 Mar 2016 21:47:01 +1100 Subject: Re: [RFC PATCH v4 0/7] vfio-pci: Allow to mmap sub-page MMIO BARs and MSI-X table To: Bjorn Helgaas References: <1457336918-3893-1-git-send-email-xyjxie@linux.vnet.ibm.com> <56E93ACC.7080403@linux.vnet.ibm.com> <20160316141013.GA21809@localhost> Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-doc@vger.kernel.org, bhelgaas@google.com, corbet@lwn.net, aik@ozlabs.ru, alex.williamson@redhat.com, benh@kernel.crashing.org, paulus@samba.org, mpe@ellerman.id.au, warrier@linux.vnet.ibm.com, zhong@linux.vnet.ibm.com, nikunj@linux.vnet.ibm.com From: Yongji Xie Message-ID: <56EA8B14.4070808@linux.vnet.ibm.com> Date: Thu, 17 Mar 2016 18:46:44 +0800 MIME-Version: 1.0 In-Reply-To: <20160316141013.GA21809@localhost> Content-Type: text/plain; charset=utf-8; format=flowed List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 2016/3/16 22:10, Bjorn Helgaas wrote: > On Wed, Mar 16, 2016 at 06:51:56PM +0800, Yongji Xie wrote: >> Ping. > This is mainly VFIO stuff, and Alex had some security concerns, so I'm > not going to spend much time looking at this until he's satisfied. > > When I do, I'll be looking hard at the resource_alignment kernel > parameter. I'm opposed to kernel parameters in general because > they're very difficult for users to use correctly, and they lead to > kernel code paths that are rarely tested and hard to maintain. So > I'll be looking for an excuse to reject changes in that area. > > The changelog for 2/7 says it "replaces IORESOURCE_STARTALIGN with > IORESOURCE_WINDOW." But even a glance at the patch itself shows that > IORESOURCE_WINDOW is *added* to some places, and it doesn't *replace* > IORESOURCE_STARTALIGN. There is a problem with my statement. I mean we can use IORESOURCE_WINDOW to identify bridge resources instead of IORESOURCE_STARTALIGN here. > The changelog for 4/7 says: > > This is because vfio will not allow to passthrough one BAR's mmio > page which may be shared with other BARs. To solve this performance > issue ... > > with no mention at all of the actual *reason* vfio doesn't allow that > passthrough. If I understand correctly, that reason has to do with > security, so your justification must be much stronger than "solving a > performance issue." OK. I will try to make my justification become stronger. Thanks, Yongji Xie