Re: [RFC PATCH 3/5] hw/pci-host/bonito: Remap PCI "lo" regions when PCIMAP reg is modified

[Peter Maydell]

On Sat, 2 Jan 2021 at 11:22, BALATON Zoltan <balaton@eik.bme.hu> wrote:
> I have similar code in the series I've just posted where I'm mapping
> regions of serial devices. I did consider using set_enabled and
> set_address but ended up with removing and adding regions because I'm not
> sure what happens if guest tries to move one region over another like
> having one region at a default location while guest tries to map the other
> one there (the pegasos2 maps serial at 0x2f8 which is normally COM2 on a
> PC). This should not happen in theory but when removing disabled regions
> it cannot happen so that looks safer therefore I chose to do that. Not
> sure if this could be a problem here just shared my thughts about this.

I'm not sure what you have in mind -- could you explain further?
There should be no difference as far as the MemoryRegion handling
code is concerned between "this memory region is marked disabled" and
"the memory region was deleted and will be created from fresh and added
back later" -- an MR that's in the hierarchy but not enabled is
entirely ignored, as if it wasn't there at all, when creating the
flat-view.

That said, doing memory_region_del_subregion()/memory_region_add_subregion()
I think is also OK -- what's definitely not required is actually
deleting and recreating the MRs the way this code is doing.

thanks
-- PMM