x86/PCI: Disable E820 reserved region clipping starting in 2023
Some firmware includes unusable space (host bridge registers, hidden PCI device BARs, etc) in PCI host bridge _CRS. As far as we know, there's nothing in the ACPI, UEFI, or PCI Firmware spec that requires the OS to remove E820 reserved regions from _CRS, so this seems like a firmware defect. As a workaround,4dc2287c18
("x86: avoid E820 regions when allocating address space") has clipped out the unusable space in the past. This is required for machines like the following: - Dell Precision T3500 (the original motivator for4dc2287c18
); see https://bugzilla.kernel.org/show_bug.cgi?id=16228 - Asus C523NA (Coral) Chromebook; see https://lore.kernel.org/all/4e9fca2f-0af1-3684-6c97-4c35befd5019@redhat.com/ - Lenovo ThinkPad X1 Gen 2; see: https://bugzilla.redhat.com/show_bug.cgi?id=2029207 But other firmware supplies E820 reserved regions that cover entire _CRS windows, and clipping throws away the entire window, leaving none for hot-added or uninitialized devices. This clipping breaks a whole range of Lenovo IdeaPads, Yogas, Yoga Slims, and notebooks, as well as Acer Spin 5 and Clevo X170KM-G Barebone machines. E820 reserved entries that cover a memory-mapped PCI host bridge, including its registers and memory/IO windows, are probably *not* a firmware defect. Per ACPI v5.4, sec 15.2, the E820 memory map may include: Address ranges defined for baseboard memory-mapped I/O devices, such as APICs, are returned as reserved. Disable the E820 clipping by default for all post-2022 machines. We already have quirks to disable clipping for pre-2023 machines, and we'll likely need quirks to *enable* clipping for post-2022 machines that incorrectly include unusable space in _CRS, including Chromebooks and Lenovo ThinkPads. Here's the rationale for doing this. If we do nothing, and continue clipping by default: - Future systems like the Lenovo IdeaPads, Yogas, etc, Acer Spin, and Clevo Barebones will require new quirks to disable clipping. - The problem here is E820 entries that cover entire _CRS windows that should not be clipped out. - I think these E820 entries are legal per spec, and it would be hard to get BIOS vendors to change them. - We will discover new systems that need clipping disabled piecemeal as they are released. - Future systems like Lenovo X1 Carbon and the Chromebooks (probably anything using coreboot) will just work, even though their _CRS is incorrect, so we will not notice new ones that rely on the clipping. - BIOS updates will not require new quirks unless they change the DMI model string. If we add the date check in this commit that disables clipping, e.g., "no clipping when date >= 2023": - Future systems like Lenovo *IIL*, Acer Spin, and Clevo Barebones will just work without new quirks. - Future systems like Lenovo X1 Carbon and the Chromebooks will require new quirks to *enable* clipping. - The problem here is that _CRS contains regions that are not usable by PCI devices, and we rely on the E820 kludge to clip them out. - I think this use of E820 is clearly a firmware bug, so we have a fighting chance of getting it changed eventually. - BIOS updates after the cutoff date *will* require quirks, but only for systems like Lenovo X1 Carbon and Chromebooks that we already think have broken firmware. It seems to me like it's better to add quirks for firmware that we think is broken than for firmware that seems unusual but correct. [bhelgaas: comment and commit log] Link: https://lore.kernel.org/linux-pci/20220518220754.GA7911@bhelgaas/ Link: https://lore.kernel.org/r/20220519152150.6135-4-hdegoede@redhat.com Signed-off-by: Hans de Goede <hdegoede@redhat.com> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Cc: Benoit Grégoire <benoitg@coeus.ca> Cc: Hui Wang <hui.wang@canonical.com>
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@ -200,6 +200,27 @@ void __init pci_acpi_crs_quirks(void)
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if (year >= 0 && year < 2008 && iomem_resource.end <= 0xffffffff)
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pci_use_crs = false;
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/*
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* Some firmware includes unusable space (host bridge registers,
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* hidden PCI device BARs, etc) in PCI host bridge _CRS. This is a
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* firmware defect, and 4dc2287c1805 ("x86: avoid E820 regions when
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* allocating address space") has clipped out the unusable space in
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* the past.
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*
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* But other firmware supplies E820 reserved regions that cover
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* entire _CRS windows, so clipping throws away the entire window,
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* leaving none for hot-added or uninitialized devices. These E820
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* entries are probably *not* a firmware defect, so disable the
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* clipping by default for post-2022 machines.
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*
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* We already have quirks to disable clipping for pre-2023
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* machines, and we'll likely need quirks to *enable* clipping for
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* post-2022 machines that incorrectly include unusable space in
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* _CRS.
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*/
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if (year >= 2023)
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pci_use_e820 = false;
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dmi_check_system(pci_crs_quirks);
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/*
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