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From: Gerd Hoffmann <kraxel@redhat.com>
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Subject: Re: [Qemu-devel] [RFC] map 64-bit PCI devices after all possible RAM
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>, kevin@koconnor.net, seabios@seabios.org, qemu-devel@nongnu.org, pbonzini@redhat.com

  Hi,

> I think the simplest way to do all this is simply to tell seabios
> that we have more memory. seabios already programs 64 bit BARs
> higher than memory.

Hmm?  As I understand Igor just wants some address space for memory
hotplug.  So there wouldn't be memory there (yet).  And telling seabios
there is although there isn't will make seabios place wrong info into
the e820 tables.  Not going to fly.

> I think the issue is with legacy guests.
> E.g. if VCPU claims to support 50 bit of memory
> do we put high PCI memory at 1 << 50?
> If yes old guests which expect at most 40 bit
> will not be able to use it.

Hmm.  Sure such guests exist?  Note this is physical address lines, not
virtual address space (where you might need an additional level of
pagetables to fully use it, which is not something we could expect old
guests being able to handle).

cheers,
  Gerd