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: Wed, 05 Jun 2013 16:07:18 -0700
Message-ID: <51AFC4A6.6070607@zytor.com>
References: <20130530140132.GC21440@redhat.com>
	<874ndgujiw.fsf@rustcorp.com.au> <20130603101136.GB8649@redhat.com>
	<87fvwytpa1.fsf@rustcorp.com.au>
	<20130604064216.GD19433@redhat.com> <871u8g67d6.fsf@codemonkey.ws>
	<20130605140936.GB10604@redhat.com> <87ehcgr3wq.fsf@codemonkey.ws>
	<20130605151953.GA25987@redhat.com> <87bo7ktvaw.fsf@codemonkey.ws>
	<20130605162029.GB26561@redhat.com>
	<51AFA92B.2030203@zytor.com> <87fvwwmdmf.fsf@codemonkey.ws>
	<51AFB3DD.1050902@zytor.com> <874ndcb47i.fsf@codemonkey.ws>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Return-path: <virtualization-bounces@lists.linux-foundation.org>
In-Reply-To: <874ndcb47i.fsf@codemonkey.ws>
List-Unsubscribe: <https://lists.linuxfoundation.org/mailman/options/virtualization>,
	<mailto:virtualization-request@lists.linux-foundation.org?subject=unsubscribe>
List-Archive: <http://lists.linuxfoundation.org/pipermail/virtualization/>
List-Post: <mailto:virtualization@lists.linux-foundation.org>
List-Help: <mailto:virtualization-request@lists.linux-foundation.org?subject=help>
List-Subscribe: <https://lists.linuxfoundation.org/mailman/listinfo/virtualization>,
	<mailto:virtualization-request@lists.linux-foundation.org?subject=subscribe>
Sender: virtualization-bounces@lists.linux-foundation.org
Errors-To: virtualization-bounces@lists.linux-foundation.org
To: Anthony Liguori <aliguori@us.ibm.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>
List-Id: virtualization@lists.linuxfoundation.org

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.

	-hpa