Re: [PATCH v16 5/9] conf: Introduce SGX EPC element into device memory xml

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On 10/8/22 06:00, Lin Yang wrote:
> With NUMA config:
> 
> <devices>
>   ...
>   <memory model='sgx-epc'>
>     <source>
>       <nodemask>0-1</nodemask>
>     </source>
>     <target>
>       <size unit='KiB'>512</size>
>       <node>0</node>
>     </target>
>   </memory>
>   ...
> </devices>
> 
> Without NUMA config:
> 
> <devices>
>   ...
>   <memory model='sgx-epc'>
>     <target>
>       <size unit='KiB'>512</size>
>     </target>
>   </memory>
>   ...
> </devices>


Patches look good to me. And I'd like to merge them. However, in one of
previous iterations Peter raised a concern whether this should be
exposed as something else than <memory model='sgx-epc'/>. One fact that
would support this is that SGX 'cuts' from guest memory. I mean, memory
backend-epc does not add more RAM into the guest:

# ./qemu-system-x86_64 -S -nographic -nodefaults -m 128 \
-machine pc,sgx-epc.0.memdev=memepc0,sgx-epc.0.node=0 \
-object '{"qom-type":"memory-backend-epc","id":"memepc0","prealloc":true,"size":67108864,"host-nodes":[0],"policy":"bind"}' \
-monitor stdio
QEMU 7.1.50 monitor - type 'help' for more information
(qemu) info memory-devices 
Memory device [sgx-epc]: ""
  memaddr: 0x100000000
  size: 67108864
  node: 0
  memdev: /objects/memepc0
(qemu) info memory_size_summary 
base memory: 134217728
plugged memory: 0
(qemu) 


Which is also the reason why we need to special case
VIR_DOMAIN_MEMORY_MODEL_SGX_EPC so much.

On the other hand, the fact that QEMU exposes it as a memory backend
means, that it kind of falls into <memory/> category.

So my question then is, Peter, are you okay with leaving this under
<memory/> or do you have other suggestion?

Michal




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