Re: SMRAM sizes on large hosts

[Laszlo Ersek <lersek@redhat.com>]

On 05/04/17 16:52, Gerd Hoffmann wrote:
>   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.

My thoughts exactly!

Thank you,
Laszlo