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List:       qemu-discuss
Subject:    Re: [Qemu-discuss] Devdax backend for vnvdimm not working
From:       Kamal Kakri <kamalkakri2017 () yahoo ! com>
Date:       2019-01-15 22:51:09
Message-ID: 2050085823.124754.1547592669568 () mail ! yahoo ! com
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 My devdax device is 2MB aligned so I dont think this is alignment related.# ndctl \
list -X -n namespace0.0 [
   {
       "dev":"namespace0.0",
       "mode":"devdax",
       "map":"dev",
       "size":16909336576,
       "uuid":"e5265c0a-d902-41ce-b1d1-87a78c358aa4",
       "daxregion":{
           "id":0,
           "size":16909336576,
           "align":2097152,   ------------------------->
           "devices":[
               {
                   "chardev":"dax0.0",
                   "size":16909336576
               }
           ]
       }
   }
]


I even tried to create vnvdimm of exact same size as my devdax namespace, thinking \
that it would not need to ftruncate in that case but I still get the same error: # \
                virsh start fox22vm
start: domain(optdata): fox22vm
start: found option <domain>: fox22vm
start: <domain> trying as domain NAME
error: Failed to start domain fox22vm
error: internal error: qemu unexpectedly closed the monitor: ftruncate: Invalid \
argument 2019-01-15T21:58:52.647221Z qemu-kvm: -object \
memory-backend-file,id=memnvdimm0,prealloc=yes,mem-path=/dev/dax0.0,share=yes,size=16909336576: \
unable to map backing store for guest RAM: Invalid argument


Has anyone ever got devdax backed vnvdimm configured and working? 
If yes then pls let me know what libvirt/qemu/kernel version you have used to get it \
working.

Thanks.
    On Tuesday, January 15, 2019, 3:13:27 PM EST, Kamal Kakri \
<kamalkakri2017@yahoo.com> wrote:    
 Hi,

I have a namespace (backed by real nvdimm h/w) configured in devdax mode:
# ndctl list -N -n namespace0.0
[
   {
       "dev":"namespace0.0",
       "mode":"devdax",
       "map":"dev",
       "size":16909336576,
       "uuid":"e5265c0a-d902-41ce-b1d1-87a78c358aa4",
       "chardev":"dax0.0"
   }
]


When I try to configure my vm using "virsh" with something like this:
       <memory model='nvdimm' access='shared'>
           <source>
               <path>/dev/dax0.0</path>
               <align unit='KiB'>2048</align>
               <pmem/>
           </source>
           <target>
               <size unit='KiB'>2097152</size>
               <node>0</node>
           </target>
           <alias name='nvdimm0'/>
           <address type='dimm' slot='0'/>
       </memory>


I get an error while starting my vm:
# virsh start fox22vm
start: domain(optdata): fox22vm
start: found option <domain>: fox22vm
start: <domain> trying as domain NAME
error: Failed to start domain fox22vm
error: internal error: qemu unexpectedly closed the monitor: ftruncate: Invalid \
argument 2019-01-15T18:00:36.587467Z qemu-kvm: -object \
memory-backend-file,id=memnvdimm0,prealloc=yes,mem-path=/dev/dax0.0,share=yes,size=2147483648: \
unable to map backing store for guest RAM: Invalid argument

I have tried to add "align unit" to my virsh xml but it does not seem to pass it onto \
qemu (as much as I can see from the qemu cmd line in the logs at \
/var/log/libvirt/qemu)


Can anyone pls hint as to what possibly could be the issue ? Is this alignment \
related or something else ?

Here are my versions:
# virsh --version
4.5.0
[root@fox22hv libexec]# /usr/libexec/qemu-kvm --version
QEMU emulator version 2.12.0 (qemu-kvm-rhev-2.12.0-18.el7_6.1)
Copyright (c) 2003-2017 Fabrice Bellard and the QEMU Project developers
# uname -a
Linux fox22hv 4.19.0-1.el7.elrepo.x86_64 #1 SMP Mon Oct 22 10:40:32 EDT 2018 x86_64 \
x86_64 x86_64 GNU/Linux




  


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