Re: [Xen-devel] PCI delegation works, access to the delegated NIC doesn't

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 8 Mar 2006, at 23:05, Ryan wrote:

> Keir, I don't believe your patch is entirely correct. If you write a
> double-word and one byte or one word of that double-word gets picked up
> in a field in the virtual configuration space overlay but not the other
> bytes or word, the handled flag will still get set to true, but the
> remaining bytes will never be written to the device. I think correctly
> implementing this is non-trivial as you'd need to put some code up 
> above
> to track which bytes have been handled and which ones haven't. However,
> I think it's unlikely that you'd ever have this condition actually
> affect a device given the current virtual configuration space.
Yes, I'm aware of that limitation and it will be a pain to fix 
properly. Actually, it wouldn't be too bad if the list of config-space 
handlers were in sorted order. Then we could deal with the necessary 
'gaps' as we go.
Allowing permissive setting at a finer granularity is also a good idea. 
I see no problem with keeping the global flag too though. It defaults 
to safety (off), and who are we to say that a user or administrator 
should not be allowed to explicitly set such a global policy as they 
see fit?
The problem with the 'proper' fix is that it can never really be 
completed -- there'll always be some new piece of hardware that needs 
to be accounted for and which cannot be controlled from a driver domain 
without extra patching.
 -- Keir


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