On Mon, Jul 04, 2016 at 06:16:46PM +0800, Xiao Guangrong wrote: > > > On 07/04/2016 05:16 PM, Neo Jia wrote: > >On Mon, Jul 04, 2016 at 04:45:05PM +0800, 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. > > > > > >Sorry, I think I misread the "allocation" as "mapping". We only delay the > >cpu mapping, not the allocation. > > So how to understand your statement: > "at that moment nobody has any knowledge about how the physical mmio gets > virtualized" > > The resource, physical MMIO region, has been allocated, why we do not know > the physical > address mapped to the VM? >
>From a device driver point of view, the physical mmio region never gets >allocated until the corresponding resource is requested by clients and granted by the mediated device driver. The resource here is the internal hw resource. "at that moment" == vfio client triggers mmap() call. Thanks, Neo > > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html
