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    SubjectRe: [PATCH RFC] virtio-spec: flexible configuration layout
    On Wed, Nov 09, 2011 at 02:48:58PM +0200, Sasha Levin wrote:
    > On Wed, 2011-11-09 at 14:38 +0200, Avi Kivity wrote:
    > > On 11/09/2011 10:46 AM, Sasha Levin wrote:
    > > > > Alternatively we can add new structures with new
    > > > > structure IDs, pointed to from PCI configuration space.
    > > > >
    > > > > As we don't yet have devices or drivers with 64 bit features,
    > > > > I decided we don't need high feature bits in legacy space.
    > > > > This also frees up feature bit 31 as we don't need it
    > > > > to enable high feature bits anymore.
    > > >
    > > > KVM tool actually has support for 64bit features, we can probably remove
    > > > that when Pekka isn't looking :)
    > > >
    > >
    > > What about the Windows drivers?
    >
    > While 64-bit features were defined, there was no actual devices to use
    > them.
    >
    > So even if Windows drivers had the ability to support 64-bit features,
    > no device ever needed it therefore no device ever activated it.
    >
    > A potential issue might arise when we remap feature bit 31 to do
    > something else, and when activated it would fool Windows drivers to
    > think that 64-bit features are now activated, while they're not - but
    > thats not something that should happen since legacy layout shouldn't
    > have that field enabled as per the spec (no new features in legacy
    > code).
    >
    > I was unable to check if it was actually implemented in the drivers
    > because
    > http://git.kernel.org/?p=virt/kvm/kvm-guest-drivers-windows.git;a=summary is not quite there (*cough*).

    I'm pretty sure windows drivers didn't yet get to it.
    This was out for a very short time.

    > --
    >
    > Sasha.
    >


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