Re: SMRAM sizes on large hosts

[Gerd Hoffmann <kraxel@redhat.com>]

  Hi,

> If we invent such a new register, it should be in a location that is
> either read-only, or zeroed-on-reset, in current QEMU. Otherwise, new
> firmware running on old QEMU could be misled by a guest OS that writes
> to this register, and then either reboots or enters S3.

Good point, we need to be quite careful here to not open security holes.
Current state is that pretty much all pci config space is writable and
not cleared on reset.  So no easy way out.

> ... With this in mind, I don't oppose "having to write somewhere to read
> back the result", but then let's please make that write access as well
> to the same new qemu-specific register, and not to MCH_ESMRAMC.

That should work, yes.  Write '1' to the register, then read back.  If
it is still '1' -> no big tseg support.  Otherwise it returns the tseg
size in some form, and "11b" in ESMRAMC can be used to pick that.

cheers,
  Gerd