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From: Pankaj Gupta <pagupta@redhat.com>
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Subject: Re: [Qemu-devel] KVM "fake DAX" flushing interface - discussion
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To: Dan Williams <dan.j.williams@intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>, Rik van Riel <riel@redhat.com>, Xiao Guangrong <xiaoguangrong.eric@gmail.com>, Christoph Hellwig <hch@infradead.org>, Jan Kara <jack@suse.cz>, Stefan Hajnoczi <stefanha@redhat.com>, Stefan Hajnoczi <stefanha@gmail.com>, kvm-devel <kvm@vger.kernel.org>, Qemu Developers <qemu-devel@nongnu.org>, "linux-nvdimm@lists.01.org" <linux-nvdimm@ml01.01.org>, ross zwisler <ross.zwisler@linux.intel.com>, Kevin Wolf <kwolf@redhat.com>, Nitesh Narayan Lal <nilal@redhat.com>, Haozhong Zhang <haozhong.zhang@intel.com>, Ross Zwisler <ross.zwisler@intel.com>


Hello Dan,

> Not a flag, but a new "Address Range Type GUID". See section "5.2.25.2
> System Physical Address (SPA) Range Structure" in the ACPI 6.2A
> specification. Since it is a GUID we could define a Linux specific
> type for this case, but spec changes would allow non-Linux hypervisors
> to advertise a standard interface to guests.
> 

I have added new SPA with a GUUID for this memory type and I could add 
this new memory type in System memory map. I need help with the namespace
handling for this new type As mentioned in [1] discussion:

- Create a new namespace for this new memory type
- Teach libnvdimm how to handle this new namespace 

I have some queries on this:

1] How namespace handling of this new memory type would be?
  
2] There are existing namespace types: 
  ND_DEVICE_NAMESPACE_IO, ND_DEVICE_NAMESPACE_PMEM, ND_DEVICE_NAMESPACE_BLK

  How libnvdimm will handle this new name-space type in conjuction with existing
  memory type, region & namespaces?  

3] For sending guest to host flush commands we still have to think about some 
   async way?
    
[1] https://lists.gnu.org/archive/html/qemu-devel/2017-07/msg08404.html 

Thanks,
Pankaj