Re: [PATCH v10 27/45] hw/cxl/host: Add support for CXL Fixed Memory Windows.

[Paolo Bonzini <pbonzini@redhat.com>]

On 4/29/22 16:40, Jonathan Cameron via wrote:
> From: Jonathan Cameron <jonathan.cameron@huawei.com>
> 
> The concept of these is introduced in [1] in terms of the
> description the CEDT ACPI table. The principal is more general.
> Unlike once traffic hits the CXL root bridges, the host system
> memory address routing is implementation defined and effectively
> static once observable by standard / generic system software.
> Each CXL Fixed Memory Windows (CFMW) is a region of PA space
> which has fixed system dependent routing configured so that
> accesses can be routed to the CXL devices below a set of target
> root bridges. The accesses may be interleaved across multiple
> root bridges.
> 
> For QEMU we could have fully specified these regions in terms
> of a base PA + size, but as the absolute address does not matter
> it is simpler to let individual platforms place the memory regions.
> 
> ExampleS:
> -cxl-fixed-memory-window targets.0=cxl.0,size=128G
> -cxl-fixed-memory-window targets.0=cxl.1,size=128G
> -cxl-fixed-memory-window targets.0=cxl0,targets.1=cxl.1,size=256G,interleave-granularity=2k

Sorry for the late review, but: no more command line options should
be added to QEMU.  This should be:

-M cxl-fmw.0.targets.0=cxl.0,cxl-fmw.0.size=128G \
-M cxl-fmw.1.targets.0=cxl.1,cxl-fmw.1.size=128G \
-M cxl-fmw.2.targets.0=cxl.0,cxl-fmw.2.targets.1=cxl.1,cxl-fmw.2.size=128G,cxl-fmw.2.interleave-granularity=2k

I'm not against adding a shortcut as above, but the implementation should
be entirely in MachineState using a QOM property.

The reason for this is that we're looking into doing machine setup entirely
via RPC, and any extra option is a new command to be implemented.

Would you be able to do the change?  Since you are already using QAPI to
deserialize the option it should not be hard.  I can promise a quick review,
and I can also provide with an example conversion for -boot at
https://lore.kernel.org/r/20220414165300.555321-3-pbonzini@redhat.com/.

Paolo