Firmware can use EfiMemoryMappedIO to request that MMIO regions be mapped
by the OS so they can be accessed by EFI runtime services, but should have
no other significance to the OS (UEFI r2.10, sec 7.2).  However, most
bootloaders and EFI stubs convert EfiMemoryMappedIO regions to
E820_TYPE_RESERVED entries, which prevent Linux from allocating space from
them (see remove_e820_regions()).

Some platforms use EfiMemoryMappedIO entries for PCI MMCONFIG space and PCI
host bridge windows, which means Linux can't allocate BAR space for
hot-added devices.

Remove large EfiMemoryMappedIO regions from the E820 map to avoid this
problem.

Leave small (< 256KB) EfiMemoryMappedIO regions alone because on some
platforms, these describe non-window space that's included in host bridge
_CRS.  If we assign that space to PCI devices, they don't work.  On the
Lenovo X1 Carbon, this leads to suspend/resume failures.

The previous solution to the problem of allocating BARs in these regions
was to add pci_crs_quirks[] entries to disable E820 checking for these
machines (see d341838d ("x86/PCI: Disable E820 reserved region clipping
via quirks")):

  Acer   DMI_PRODUCT_NAME    Spin SP513-54N
  Clevo  DMI_BOARD_NAME      X170KM-G
  Lenovo DMI_PRODUCT_VERSION *IIL*

Florent reported the BAR allocation issue on the Clevo NL4XLU.  We could
add another quirk for the NL4XLU, but I hope this generic change can solve
it for many machines without having to add quirks.

This change has been tested on Clevo X170KM-G (Konrad) and Lenovo Ideapad
Slim 3 (Matt) and solves the problem even when overriding the existing
quirks by booting with "pci=use_e820".

Link: https://bugzilla.kernel.org/show_bug.cgi?id=216565     Clevo NL4XLU
Link: https://bugzilla.kernel.org/show_bug.cgi?id=206459#c78 Clevo X170KM-G
Link: https://bugzilla.redhat.com/show_bug.cgi?id=1868899    Ideapad Slim 3
Link: https://bugzilla.redhat.com/show_bug.cgi?id=2029207    X1 Carbon
Link: https://lore.kernel.org/r/20221208190341.1560157-2-helgaas@kernel.orgReported-by: Florent DELAHAYE <kernelorg@undead.fr>
Tested-by: Konrad J Hambrick <kjhambrick@gmail.com>
Tested-by: Matt Hansen <2lprbe78@duck.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>