Re: [Qemu-devel] Suggestion on 'virtio-pmem' implementation

[David Hildenbrand]

Hi Pankaj,

I have a prototype (new one for virtio-mem I was working on over the last 
weeks) for exactly what you need. I basically factored out the notion of a 
memory device. So also virtio devices can be memory devices and get recognized 
e.g. in formerly known pc_dimm_get_free_address(), so it works out nicely with 
ordinary memory hotplug and such. 

Guess your main problem right now is that you don‘t create a memory slot 
properly. But I also have code for that that you can built onto.

I‘m right now in Sri Lanka on vacation, I‘ll be back on 23. September and will 
send you the link to a branch with the prototype asap.

Thanks,

David / dhildenb / address@hidden

Von meinem iPhone gesendet

> Am 14.03.2018 um 10:36 schrieb Pankaj Gupta <address@hidden>:
> 
> 
> 
> Hi,
> 
> 
> I am implementing 'virtio-pmem' as a mechanism to
> flush guest writes with 'fake DAX' flushing interface.
> 
> Below is the high level details of components:
> 
> 1] 'virtio-pmem' device expose guest physical address
>  details(start, len).   
> 
> 2] 'virtio-pmem' driver in guest discovers this 
>    information and configures 'libnvdimm'. Guest 'pmem' 
>    driver works on this memory range.
> 
> 3] Guest 'pmem' driver uses 'virtio-pmem' PV driver to 
>   send flush commands.
> 
> 
> I need suggestion implementing part 1]
> 
> * When tried with 'hotplug_memory.base' address as guest physical 
>  address, I am facing 'EPT_MISCONFIG' errors when pmem does mkfs. 
>  After digging more it looks like address range I am using as guest
>  physical address is either already mapped as MMIO or reserved. 
>  Though Guest hot-plugs this physical address into its virtual 
>  memory range when guest tries to read/write the memory KVM cannot 
>  translate the address and throw 'EPT_MISCONFIG' error.
> 
> * While I am trying to get the appropriate guest physical address
>  which is free, I could see memory 'pc_dimm_memory_plug' code 
>  has a function 'pc_dimm_get_free_addr' which works with 'PC DIMM'
>  class. As I am using 'VIRTIO', there is no way AFAIK this function 
>  can be used by VIRTIO or my PV device code.
> 
> 
> I need ideas to get the free guest physical address from my PV 
> device code so that we can use this range in guest address space.
> 
> Find below pointer to previous discussion:
> 
> https://marc.info/?l=kvm&m=151629709903946&w=2
> 
> Thanks,
> Pankaj  
>