Re: A confusion about CXL in arm virt machine

[Gregory Price]

On Fri, Jun 16, 2023 at 03:43:31PM +0800, Yuquan Wang wrote:
> Hi, Gregory
> 
> There is one confusion about CXL in QEMU I hope to consult. 
> If you have some time to look at this email, I would have better 
> understanding of CXL 
> emulation in QEMU.
> 
> On docs/system/devices/cxl.rst ,  Gregory wrote:
> A very simple setup with just one directly attached CXL Type 3 Volatile 
> Memory device::
> qemu-system-aarch64 -M virt,gic-version=3,cxl=on -m 4g,maxmem=8G,slots=8 -cpu 
> max \
> ......
> 
> As the current master branch of QEMU has not yet complemented the CXL 
> option/expansion 
> in arm virt machine, how this example command lines worked? Or here used 
> another branch 
> rather than master?
> 
> Many thanks
> Yuquan

As of today, the qemu/qemu.git master branch does have the required
patch for volatile region support: adacc814f541af9281c922e750d8ba4b90c1a73e

however, the last time i tested it on x86, the master branch was
incapable of enabling these regions with the latest kernel (6.3.x)
despite that kernel having sufficient support to do so.  I have not dug
into what the discrepency between master and johnathan's working branch
are just yet.

Last I tested cxl-2023-05-25 branch of Johnathan's fork is working on x86: 

https://gitlab.com/jic23/qemu/-/tree/cxl-2023-05-25

I have not worked with the ARM machine, but Johnathan may be able to
comment on the state of ARM support for this code.

~Gregory