From mboxrd@z Thu Jan  1 00:00:00 1970
From: Anthony Liguori <aliguori@us.ibm.com>
Subject: Re: [PATCH RFC] virtio-pci: new config layout: using memory BAR
Date: Wed, 05 Jun 2013 19:41:17 -0500
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To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Peter Maydell <peter.maydell@linaro.org>, kvm@vger.kernel.org, "Michael S. Tsirkin" <mst@redhat.com>, virtualization@lists.linux-foundation.org, Stefan Hajnoczi <stefanha@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, KONRAD Frederic <fred.konrad@greensocs.com>
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"H. Peter Anvin" <hpa@zytor.com> writes:

> On 06/05/2013 03:08 PM, Anthony Liguori wrote:
>>>
>>> Definitely an option.  However, we want to be able to boot from native
>>> devices, too, so having an I/O BAR (which would not be used by the OS
>>> driver) should still at the very least be an option.
>> 
>> What makes it so difficult to work with an MMIO bar for PCI-e?
>> 
>> With legacy PCI, tracking allocation of MMIO vs. PIO is pretty straight
>> forward.  Is there something special about PCI-e here?
>> 
>
> It's not tracking allocation.  It is that accessing memory above 1 MiB
> is incredibly painful in the BIOS environment, which basically means
> MMIO is inaccessible.

Oh, you mean in real mode.

SeaBIOS runs the virtio code in 32-bit mode with a flat memory layout.
There are loads of ASSERT32FLAT()s in the code to make sure of this.

Regards,

Anthony Liguori

>
> 	-hpa
>
>
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