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. Thanks, Neo > > >
