Re: CXL volatile memory is not listed

[Jonathan Cameron via <qemu-devel@nongnu.org>]

On Wed, 9 Aug 2023 04:21:47 +0530
Maverickk 78 <maverickk1778@gmail.com> wrote:

> Hello,
> 
> I am running qemu-system-x86_64
> 
> qemu-system-x86_64 --version
> QEMU emulator version 8.0.92 (v8.1.0-rc2-80-g0450cf0897)
>
+Cc linux-cxl as the answer is more todo with linux than qemu.
 
> qemu-system-x86_64 \
> -m 2G,slots=4,maxmem=4G \
> -smp 4 \
> -machine type=q35,accel=kvm,cxl=on \
> -enable-kvm \
> -nographic \
> -device pxb-cxl,id=cxl.0,bus=pcie.0,bus_nr=52 \
> -device cxl-rp,id=rp0,bus=cxl.0,chassis=0,port=0,slot=0 \
> -object memory-backend-file,id=mem0,mem-path=/tmp/mem0,size=1G,share=true \
> -device cxl-type3,bus=rp0,volatile-memdev=mem0,id=cxl-mem0 \
> -M cxl-fmw.0.targets.0=cxl.0,cxl-fmw.0.size=1G

There are some problems upstream at the moment (probably not cxl related but
I'm digging). So today I can't boot an x86 machine. (goody)


More generally for the flow that would bring the memory up as system ram
you would typically need the bios to have done the CXL enumeration or
a bunch of scripts in the kernel to have done it.  In general it can't
be fully automated, because there are policy decisions to make on things like
interleaving.

I'm not aware of any open source BIOSs that do it yet.  So you have
to rely on the same kernel paths as for persistent memory - manual configuration
etc in the kernel. 

There is support in ndctl for those enabling flows, so I'd look there
for more information

Jonathan


> 
> 
> I was expecting the CXL memory to be listed in "System Ram", the lsmem
> shows only 2G memory which is System RAM, it's not listing the CXL
> memory.
> 
> Do I need to pass any particular parameter in the kernel command line?
> 
> Is there any documentation available? I followed the inputs provided in
> 
> https://lore.kernel.org/linux-mm/Y+CSOeHVLKudN0A6@kroah.com/T/
> 
> Is there any documentation/blog listed?