RE: [Xen-devel] [PATCH][RFC] Support more Capability Structures andDevice Specific

["Dong, Eddie" <eddie.dong@xxxxxxxxx>]

> I haven't read many modern PCI card specs but with the
> constant 
> shifting of functionality (even functionality which is
> intended to 
> preserve hardware integrity) to software and firmware, I
> would be wary 
> of assuming that every unknown PCI card has no register
> and 
> configuration settings which can cause hardware damage or
> other kinds 
> of unexpected and undesirable events.

For those vendor specific registers (in PCI cap or not), we always have
dillemma: pass through with functionality or discard with malfunction.
If we pass through them, then the opposite card are in black list that
we can't support, if we discard them, the former class of card becomes
un-assignable.

Per current data, pass through get many known bug fixed as the case
Dexuan mentioned. But we didn't see a HW damaging host. Some know issue
could be a device issuing tons of PCIe traffic, absorbing extra power,
issuing interrupt storm etc, but right now we didn't see issues yet.

> 
> If there is there a requirement written into the general
> PCI 
> specification that this won't happen, then fine - if so
> please quote 
> chapter and verse.
> 
Defintely if PCIe spec can be modified to support this one is best, but
we still have legacy devices.

Thx, eddie


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