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Subject[PATCH] Fix coalescing host bridge windows in arch/x86/pci/acpi.c
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[Resending due to no response to the original message in a week]

Hi all,

I have a board with a BIOS bug that reports the following I/O port regions in
_CRS on one of the host bridges:

0x0000-0x03af // #0
0x03e0-0x0cf7 // #1
0x03b0-0x03bb // #2
0x03c0-0x03df // #3
0x0000-0xdfff // #4
0xf000-0xffff // #5

Obviously, region number #4 is erroneous as it overlaps with regions #0..3.
The code in coalesce_windows() in arch/x86/pci/acpi.c attempts to recover from
such kind of BIOS bugs by merging the overlapping regions. Current code
expands region #0 to 0x0000-0xdffff and makes region #4 ignored. As a result,
overlap of the expanded region #0 with regions #1..3 remains undetected (as
the inner loop already compared them with region #0). As a result, regions
#1..3 are inserted into the resource tree even though they overlap with
adjusted region #0 - which later results in resource conflicts for PCI devices
with IO ports in one of those regions (e.g., for an PCI IDE controller in
legacy mode - which has port 0x3f6). The kernel then refuses to initialize
these devices.

The fix: instead of expanding res1 and ignoring res2, do the opposite. The
res2 window is yet to be compared against all windows between res1 and res2
(regions #1..3 in the above example), so the resulting resource map will
include just the expanded region - and will ignore any overlapping ones.

Signed-off-by: Alexey Neyman <stilor@att.net>diff --git a/arch/x86/pci/acpi.c b/arch/x86/pci/acpi.c
index b30e937..7fb24e5 100644
--- a/arch/x86/pci/acpi.c
+++ b/arch/x86/pci/acpi.c
@@ -354,12 +354,12 @@ static void coalesce_windows(struct pci_root_info *info, unsigned long type)
* the kernel resource tree doesn't allow overlaps.
*/
if (resource_overlaps(res1, res2)) {
- res1->start = min(res1->start, res2->start);
- res1->end = max(res1->end, res2->end);
+ res2->start = min(res1->start, res2->start);
+ res2->end = max(res1->end, res2->end);
dev_info(&info->bridge->dev,
"host bridge window expanded to %pR; %pR ignored\n",
- res1, res2);
- res2->flags = 0;
+ res2, res1);
+ res1->flags = 0;
}
}
}
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