Re: [kvm-ppc-devel] booting from virtio-blk

[Anthony Liguori <aliguori@us.ibm.com>]

Benjamin Herrenschmidt wrote:
> On Tue, 2008-04-01 at 12:09 -0500, Anthony Liguori wrote:
>
>   
>> It's the unfortunate side-effect of using PCI config space without 
>> passing it's semantics through to the virtio devices.  Right now, you do 
>> a config_get which is basically a memcpy.  If we didn't do accesses with 
>> ioread8(), you could potentially have a caller than did a config_get() 
>> of size 4 that didn't intend on having endian conversion applied.
>>
>> The other option would have been to provide config_get() and 
>> config_get8/16/32/64() the later performing endian conversion.
>>     
>
> Config space should be 8/16/32. Is that ever bridged to real PCI config
> space anyway ? Or only virtio ? And it should be endian swapped at the
> low level, either by your HV calls or by the low level kernel. Always.
> That's how PCI config space is supposed to work.
>   

I guess the point is, is that virtio config space is an abstraction with 
the implementation that is based on PCI converting all accesses to a 
series of 8-bit accesses.  The virtio config space happens to be little 
endian just like the PCI config space.

Regards,

Anthony Liguori

> Ben.
>
>   


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