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

[Pankaj Gupta <pagupta@redhat.com>]

Hi David,

> 
> 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.

Nice. This is very useful re-factoring.

> 
> 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.

sure.

> 
> 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.

Cool. Enjoy your vacation and thanks for the reply.

Best regards,
Pankaj

> 
> Thanks,
> 
> David / dhildenb / david@redhat.com
> 
> Von meinem iPhone gesendet
> 
> > Am 14.03.2018 um 10:36 schrieb Pankaj Gupta <pagupta@redhat.com>:
> > 
> > 
> > 
> > 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
> > 
>