Re: Question to mem-path support at QEMU for Xen

[Igor Mammedov]

On Tue, 26 Jul 2022 15:27:07 +0800
Huang Rui <ray.huang@amd.com> wrote:

> Hi Anthony and other Qemu/Xen guys,
> 
> We are trying to enable venus on Xen virtualization platform. And we would
> like to use the backend memory with memory-backend-memfd,id=mem1,size=4G
> options on QEMU, however, the QEMU will tell us the "-mem-path" is not
> supported with Xen. I verified the same function on KVM.
> 
> qemu-system-i386: -mem-path not supported with Xen
> 
> So may I know whether Xen has any limitation that support
> memory-backend-memfd in QEMU or just implementation is not done yet?

Currently Xen doesn't use guest RAM allocation the way the rest of
accelerators do. (it has hacks in memory_region/ramblock API,
that divert RAM allocation calls to Xen specific API)

The sane way would extend Xen to accept RAM regions (whatever they are
ram or fd based) QEMU allocates instead of going its own way. This way
it could reuse all memory backends that QEMU provides for the rest of
the non-Xen world. (not to mention that we could drop non trivial
Xen hacks so that guest RAM handling would be consistent with other
accelerators)

> Looking forward to your reply!
> 
> Thanks a lot,
> Ray
>