Re: [PATCH 02/11] PCI: Add pci_bus_isolation()

[Jason Gunthorpe <jgg@nvidia.com>]

On Thu, Jul 03, 2025 at 05:08:46PM -0600, Alex Williamson wrote:
> BTW, spec 6.0.1, section 6.12:
> 
>   For ACS requirements, single-Function devices that are SR-IOV capable
>   must be handled as if they were Multi-Function Devices, since they
>   essentially behave as Multi-Function Devices after their Virtual
>   Functions (VFs) are enabled.
> 
> Also, section 7.7.11:
> 
>   If an SR-IOV Capable Device other than one in a Root Complex
>   implements internal peer-to-peer transactions, ACS is required, and
>   ACS P2P Egress Control must be supported.

Oh, I haven't seen that one yet..

> The latter says to me that a non root complex SR-IOV device that does
> not implement ACS does not implement internal p2p routing.  

Great

> OTOH, the former seems to suggest that we need to consider VFs as
> peers of the PF

Yes, I think both are saying that. 7.7.11 talks about "internal
peer-to-peer transactions" which is exactly what ACS for a MFD is
about.

So it seems VF to VF is possible through internal transactions.

> maybe even governed by ACS on the PF, relative to
> MF routing.  

But here I think it is not clear - does the ACS of the PF globally
control all the VFs or should each VF have its own ACS in addition to
the PF?

The latter is certainly more useful, especially if the egress control
feature is used.

Let me ask some expert people what they know.

Thanks,
Jason