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 16:19:20 +0800 |
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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?
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