From mboxrd@z Thu Jan  1 00:00:00 1970
From: "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH RFC] virtio-pci: new config layout: using memory BAR
Date: Thu, 06 Jun 2013 06:53:26 -0700
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To: Gleb Natapov <gleb@redhat.com>
Cc: Peter Maydell <peter.maydell@linaro.org>, Anthony Liguori <aliguori@us.ibm.com>, 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>
List-Id: virtualization@lists.linuxfoundation.org

On 06/05/2013 11:34 PM, Gleb Natapov wrote:
>>
>> 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.
>>
> Well, not exactly. Initialization is done in 32bit, but disk
> reads/writes are done in 16bit mode since it should work from int13
> interrupt handler. The only way I know to access MMIO bars from 16 bit
> is to use SMM which we do not have in KVM.
> 

In some ways it is even worse for PXE, since PXE is defined to work from
16-bit protected mode... but the mechanism to request a segment mapping
for the high memory area doesn't actually work.

	-hpa