Re: [PATCH] thunderbolt: Make iommu_dma_protection more accurate

[Lukas Wunner <lukas@wunner.de>]

On Fri, Mar 18, 2022 at 03:51:21PM +0100, Lukas Wunner wrote:
> On Fri, Mar 18, 2022 at 02:08:16PM +0000, Robin Murphy wrote:
> > OK, so do we have any realistic options for identifying the correct PCI
> > devices, if USB4 PCIe adapters might be anywhere relative to their
> > associated NHI? Short of maintaining a list of known IDs, the only thought I
> > have left is that if we walk the whole PCI segment looking specifically for
> > hotplug-capable Gen1 ports, any system modern enough to have Thunderbolt is
> > *probably* not going to have any real PCIe Gen1 hotplug slots, so maybe
> > false negatives might be tolerable, but it still feels like a bit of a
> > sketchy heuristic.
> 
> The Thunderbolt Device ROM contains the PCI slot number, so you can
> correlate the Thunderbolt switch ports with PCIe downstream ports
> and know exactly where PCIe tunnels are terminated.
[...]
> I implemented that in 2018, so it won't apply cleanly to current
> mainline.  But I kept forward-porting it on my private branch and
> could push that to GitHub if anyone is interested.

FWIW, here's the most recent forward-port I've done:

https://github.com/l1k/linux/commits/thunderbolt_correlate_5.13