Re: [PATCH RFC] virtio-spec: flexible configuration layout

Ronen Hod
2011-11-13T14:07:43Z

On 11/09/2011 05:19 PM, Michael S. Tsirkin wrote:
> 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*).

https://github.com/YanVugenfirer/kvm-guest-drivers-windows

> 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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