[RFC 2/2] x86/PCI: Ignore EFI memmap MMIO entries

[Hans de Goede <hdegoede@redhat.com>]

Linux excludes E820 reserved addresses when allocating addresses from the
PCI host bridge window. This behavior is needed for at least 2 reasons:

1. Some BIOS-es contain a bug where they add addresses which map to system
RAM in the PCI host bridge window returned by the ACPI _CRS method, see
commit 4dc2287c1805 ("x86: avoid E820 regions when allocating address
space").

2. At least the Lenovo X1 carbon gen 2 BIOS has an overlap between an
E820 reserved range and the ACPI _CRS providing the PCI bridge windows:
 BIOS-e820: [mem 0x00000000dceff000-0x00000000dfa0ffff] reserved
 pci_bus 0000:00: root bus resource [mem 0xdfa00000-0xfebfffff window]
If Linux assigns the overlapping 0xdfa00000-0xdfa0ffff range to a PCI BAR
then the system fails to resume after a suspend.

Recently (2019) some systems have shown-up with EFI memmap MMIO entries
covering the entire _CRS returned PCI bridge memory window. These memmap
entries get converted into e820_table entries, causing all attempts to
assign memory to PCI BARs which have not been setup by the BIOS to fail.
For example see these dmesg snippets from a Lenovo IdeaPad 3 15IIL 81WE:

 efi: mem63: [MMIO   |RUN|  |  |  |  |  |  |  |  |   |  |  |  |UC] range=
     [0x0000000065400000-0x00000000cfffffff] (1708MB)
 [mem 0x000000004bc50000-0x00000000cfffffff] reserved
 pci_bus 0000:00: root bus resource [mem 0x65400000-0xbfffffff window]
 pci 0000:00:15.0: BAR 0: no space for [mem size 0x00001000 64bit]
 pci 0000:00:15.0: BAR 0: failed to assign [mem size 0x00001000 64bit]

Since the problem is specifically caused by EFI memmap entries with
a MMIO type, use the new E820_TYPE_MMIO marking of e820 entries
translated from MMIO EFI memmap entries to skip these entries when
excluding e820 reservations in arch_remove_reservations(), fixing the
problem of not being able to find free space for unassigned BARs.

BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=206459
BugLink: https://bugzilla.redhat.com/show_bug.cgi?id=1868899
BugLink: https://bugzilla.redhat.com/show_bug.cgi?id=1871793
BugLink: https://bugzilla.redhat.com/show_bug.cgi?id=2029207
BugLink: https://bugs.launchpad.net/bugs/1878279
BugLink: https://bugs.launchpad.net/bugs/1931715
BugLink: https://bugs.launchpad.net/bugs/1932069
BugLink: https://bugs.launchpad.net/bugs/1921649
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
 arch/x86/kernel/resource.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/kernel/resource.c b/arch/x86/kernel/resource.c
index 9b9fb7882c20..bd501f787a10 100644
--- a/arch/x86/kernel/resource.c
+++ b/arch/x86/kernel/resource.c
@@ -31,6 +31,10 @@ static void remove_e820_regions(struct resource *avail)
 	for (i = 0; i < e820_table->nr_entries; i++) {
 		entry = &e820_table->entries[i];
 
+		/* Some fw reserves the entire PCI bridge window as MMIO */
+		if (entry->type == E820_TYPE_MMIO)
+			continue;
+
 		resource_clip(avail, entry->addr,
 			      entry->addr + entry->size - 1);
 	}
-- 
2.33.1