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Date: Wed, 1 Jul 2015 15:50:50 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v2 02/22] virtio: run drivers in 32bit mode
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To: Gerd Hoffmann <kraxel@redhat.com>
Cc: seabios@seabios.org, qemu-devel@nongnu.org

On Wed, Jul 01, 2015 at 02:30:29PM +0200, Gerd Hoffmann wrote:
> On Mi, 2015-07-01 at 10:08 +0200, Michael S. Tsirkin wrote:
> > On Tue, Jun 30, 2015 at 10:38:53AM +0200, Gerd Hoffmann wrote:
> > > virtio version 1.0 registers can (and actually do in the qemu
> > > implementation) live in mmio space.  So we must run the blk and
> > > scsi virtio drivers in 32bit mode, otherwise we can't access them.
> > > 
> > > This also allows to drop a bunch of GET_LOWFLAT calls from the virtio
> > > code in the following patches.
> > > 
> > > Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> > 
> > Is there an advantage to running them in a 16 bit mode?
> 
> Not really any more.  Switching from 32bit mode back to
> whatever-was-active-before used to be problematic before we had smm mode
> support.  In theory.  Because you can't save/restore the complete x86
> processor state.  In practice we had surprisingly few problems,
> appearently linux boot loaders simply don't play dirty tricks.
> 
> cheers,
>   Gerd
> 

Interesting. Might not be true for non-linux loaders :)

Anyway we support SSM now so all should be well, right?

-- 
MST