Re: [BUG] hw/i386/pc.c: CXL Fixed Memory Window should not reserve e820 in bios

[Gerd Hoffmann]

>     if (pcmc->has_reserved_memory && machine->device_memory->base) {          
>    
> [...]
>                                                              
>         if (pcms->cxl_devices_state.is_enabled) {                             
>    
>             res_mem_end = cxl_resv_end;
> 
> that should be handled by this line
> 
>         }                                   
>                                      
>         *val = cpu_to_le64(ROUND_UP(res_mem_end, 1 * GiB));                   
>    
>         fw_cfg_add_file(fw_cfg, "etc/reserved-memory-end", val, 
> sizeof(*val));   
>     }  
> 
> so SeaBIOS shouldn't intrude into CXL address space

Yes, looks good, so with this in place already everyting should be fine.

> (I assume EDK2 behave similarly here)

Correct, ovmf reads that fw_cfg file too.

> > I suspect the reason for these entries to exist in the first place is to
> > inform the firmware that it should not place stuff there, and if we
>        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> just to educate me, can you point out what SeaBIOS code does with 
> reservations.

They are added to the e820 map which gets passed on to the OS.  seabios
uses (and updateas) the e820 map too, when allocating memory for
example.  While thinking about it I'm not fully sure it actually looks
at reservations, maybe it only uses (and updates) ram entries when
allocating memory.

> > remove that to conform with the spec we need some alternative way for
> > that ...
> 
> with etc/reserved-memory-end set as above,
> is E820_RESERVED really needed here?

No.  Setting etc/reserved-memory-end is enough.

So for the original patch:
Acked-by: Gerd Hoffmann <kraxel@redhat.com>

take care,
  Gerd