Re: [Qemu-devel] [PATCH v2] map 64-bit PCI BARs at location provided by emulator

[Gerd Hoffmann]

  Hi,

> Yes but at the cost of overspecifying it.
> I think it's down to the name: it's called pcimem64-start
> but it can actually be less than 4G and we need to worry what to
> do then. Also, 64 doesn't really mean >4G.
> 
> So how about "reserve-memory-over-4g"?
> bios then does 1ull << 32 + reserve-memory-over-4g
> to figure out how much to skip.

We are reaching the point where it becomes pointless bikeshedding ...

I want a interface which is clearly defined and which doesn't break if
the way we use the address space above 4g changes (hotplug,
non-contignous memory, whatever).  So make it depend on the memory
deployed isn't a clever idea.

So at the end of the day it comes down to specify an address, either
relative to 4g (your reserve-memory-over-4g suggestion) or relative to
zero (Igors pcimem64-start patch).  Both will do the job.  In both cases
the bios has to check it has no conflicts with known ram regions (i.e.
compare against 1<<32 + RamSizeAbove4G).

I personally don't see the point in having the address relative to 4g
and prefer the pcimem64-start approach.  We could rename it to
pcimem64-minimum-address to make more clear this is about keeping some
space free rather than specifyng a fixed address where the 64bit pci
bars should be mapped to.  But at the end of the day I don't care too
much, how we are going to name the baby is just a matter of taste and
not really critical for the interface ...

What is the state of the qemu side patches btw?

cheers,
  Gerd