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

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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