Messages in this thread |  | | Subject | Re: [PATCH 0/2] KVM: MMU: support VMAs that got remap_pfn_range-ed | From | Xiao Guangrong <> | Date | Mon, 4 Jul 2016 16:54:25 +0800 |
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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?
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