On Fri, Oct 14, 2022 at 01:12:28PM +0200, Michal Prívozník wrote:
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)
I'm not sure this check is showing us the truth.
In backends/hostmem-epc.c, sgx_epc_backend_memory_alloc is
opening /dev/sgx_vepc and mmap()ing the requested size from
that file. IOW that's clearly in addition to whatever has
been mapped as the main RAM.
In hw/i386/sgx-epc.c, sgx_epc_md_get_plugged_size is hardcoded
to always return 0, which is why 'plugged memory' is reported
as zero above. I don't know what it is reporting zero.
Is this because the SGX RAM is not accessible to the guest OS
as "normal" RAM perhaps, and thus to be reported differently.
With regards,
Daniel
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