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

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

Yuji Shimada wrote:
> I think it is NOT safe to pass through operations with
> unknown behaviour. qemu-dm should prevent guest software

This used to be the reason why we only pass through CMD register, but we
then suffer from that in different devices and I have to admit, without
passthrough real setting, the device won't function correctly in many
cases.

Do u have any real data ? Device memory access is fine with IOMMU, irq
vector is virtualized now.

> setting unsafe value to register.  We have to investigate
> each register and decide to emulate(virtualize) or
> passthrough. 

Investigation is defintely good, eventually we need to know all
configuration registers, but even with that, there are still device
specifc registers we have to deal such as Vendor specific capability and
those registers directly defined by devices (not a standard PCI
capability). But hidding settings due to the reason we didn't
investigate yet will simply make things worse, and we already observed
this with more devices tested such as UHCI mouse etc.


> 
> I haven't investigated some capability structures (like
> PCI-X Capability Structure).  I hide them from guest
> software. 

ditto

> 
> Device Specific Registers (exclude capability structures)
> is passthrough. In non-virtualized environment, OS does
> not touch device specific registers, but device drivers
> configure them. In virtualized environment, we have to
> allow device drivers to configure them. 

We need to pass through except the device is doing IRQ vector setting
which can't be handled in either case, those devices are simply not
assignable.

Thanks, eddie

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