From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932621AbcGDI6L (ORCPT ); Mon, 4 Jul 2016 04:58:11 -0400 Received: from mga02.intel.com ([134.134.136.20]:60562 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932106AbcGDI6I (ORCPT ); Mon, 4 Jul 2016 04:58:08 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.26,574,1459839600"; d="scan'208";a="988634414" Subject: Re: [PATCH 0/2] KVM: MMU: support VMAs that got remap_pfn_range-ed To: Neo Jia References: <1467291711-3230-1-git-send-email-pbonzini@redhat.com> <577A049A.4000402@linux.intel.com> <20160704070314.GA13291@nvidia.com> <577A123F.1060909@linux.intel.com> <20160704075302.GA13470@nvidia.com> <577A1C08.1020509@linux.intel.com> <20160704084127.GA14638@nvidia.com> <577A2211.2030906@linux.intel.com> Cc: Paolo Bonzini , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Kirti Wankhede , Andrea Arcangeli , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= From: Xiao Guangrong Message-ID: <577A2441.4090006@linux.intel.com> Date: Mon, 4 Jul 2016 16:54:25 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.8.0 MIME-Version: 1.0 In-Reply-To: <577A2211.2030906@linux.intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/04/2016 04:45 PM, Xiao Guangrong wrote: > > > On 07/04/2016 04:41 PM, Neo Jia wrote: >> On Mon, Jul 04, 2016 at 04:19:20PM +0800, Xiao Guangrong wrote: >>> >>> >>> On 07/04/2016 03:53 PM, Neo Jia wrote: >>>> On Mon, Jul 04, 2016 at 03:37:35PM +0800, Xiao Guangrong wrote: >>>>> >>>>> >>>>> On 07/04/2016 03:03 PM, Neo Jia wrote: >>>>>> On Mon, Jul 04, 2016 at 02:39:22PM +0800, Xiao Guangrong wrote: >>>>>>> >>>>>>> >>>>>>> On 06/30/2016 09:01 PM, Paolo Bonzini wrote: >>>>>>>> The vGPU folks would like to trap the first access to a BAR by setting >>>>>>>> vm_ops on the VMAs produced by mmap-ing a VFIO device. The fault handler >>>>>>>> then can use remap_pfn_range to place some non-reserved pages in the VMA. >>>>>>> >>>>>>> Why does it require fetching the pfn when the fault is triggered rather >>>>>>> than when mmap() is called? >>>>>> >>>>>> Hi Guangrong, >>>>>> >>>>>> as such mapping information between virtual mmio to physical mmio is only available >>>>>> at runtime. >>>>> >>>>> Sorry, i do not know what the different between mmap() and the time VM actually >>>>> accesses the memory for your case. Could you please more detail? >>>> >>>> Hi Guangrong, >>>> >>>> Sure. The mmap() gets called by qemu or any VFIO API userspace consumer when >>>> setting up the virtual mmio, at that moment nobody has any knowledge about how >>>> the physical mmio gets virtualized. >>>> >>>> When the vm (or application if we don't want to limit ourselves to vmm term) >>>> starts, the virtual and physical mmio gets mapped by mpci kernel module with the >>>> help from vendor supplied mediated host driver according to the hw resource >>>> assigned to this vm / application. >>> >>> Thanks for your expiation. >>> >>> It sounds like a strategy of resource allocation, you delay the allocation until VM really >>> accesses it, right? >> >> Yes, that is where the fault handler inside mpci code comes to the picture. > > > I am not sure this strategy is good. The instance is successfully created, and it is started > successful, but the VM is crashed due to the resource of that instance is not enough. That sounds > unreasonable. > Especially, you can not squeeze this kind of memory to balance the usage between all VMs. Does this strategy still make sense?