From mboxrd@z Thu Jan  1 00:00:00 1970
From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] [PATCHv2] virtio-pci: add MMIO property
Date: Tue, 20 Mar 2012 16:32:23 +0000
Message-ID: <201203201632.23939.paul@codesourcery.com>
References: <20120319203721.GA9399@redhat.com>
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Cc: "Michael S. Tsirkin" <mst@redhat.com>,
	Alexey Kardashevskiy <aik@ozlabs.ru>, rusty@rustcorp.com.au,
	kvm@vger.kernel.org, virtualization@lists.linux-foundation.org,
	avi@redhat.com, Anthony Liguori <aliguori@us.ibm.com>
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> @@ -682,10 +733,18 @@ void virtio_init_pci(VirtIOPCIProxy *proxy,
> VirtIODevice *vdev) if (size & (size-1))
>          size = 1 << qemu_fls(size);
>  
> +    proxy->bar0_mask = size - 1;

You'll get better performance if you use page-sized mappings.  You're already 
creating a mapping bigger than the actual data (rounding up to power-of-two), 
so you may as well pick a value that's convenient for qemu to map into the 
address space.

Paul