From mboxrd@z Thu Jan 1 00:00:00 1970 From: Xiao Guangrong Subject: Re: [PATCH 0/2] KVM: MMU: support VMAs that got remap_pfn_range-ed Date: Mon, 4 Jul 2016 16:19:20 +0800 Message-ID: <577A1C08.1020509@linux.intel.com> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Cc: Paolo Bonzini , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Kirti Wankhede , Andrea Arcangeli , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= To: Neo Jia Return-path: Received: from mga01.intel.com ([192.55.52.88]:61518 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750895AbcGDIXF (ORCPT ); Mon, 4 Jul 2016 04:23:05 -0400 In-Reply-To: <20160704075302.GA13470@nvidia.com> Sender: kvm-owner@vger.kernel.org List-ID: 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?