Bug report: the extended PCI config space is missed with 6.2-rc2

[Liang, Kan]

Hi Bjorn,

Happy new year!

We found some PCI issues with the latest 6.2-rc2.

- Using the lspci -xxxx, the extended PCI config space of all PCI
devices are missed with the latest 6.2-rc2. The system we used had 932
PCI devices, at least 800 which have extended space as seen when booted
into a 5.15 kernel. But none of them appeared in 6.2-rc2.
- The drivers which rely on the information in the extended PCI config
space don't work anymore. We have confirmed that the perf uncore driver
(uncore performance monitoring) and Intel VSEC driver (telemetry) don't
work in 6.2-rc2. There could be more drivers which are impacted.

After a bisect, we found the regression is caused by the below commit
07eab0901ede ("efi/x86: Remove EfiMemoryMappedIO from E820 map").
After reverting the commit, the issues are gone.

Could you please take a look at the issues?

Thanks,
Kan