linux-kernel - [PATCH] Fix coalescing host bridge windows in arch/x86/pci/acpi.c

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Message-ID: <6362938.J7ZtNEOFpc@mistral>
Date:	Sun, 22 Sep 2013 23:15:46 -0700
From:	Alexey Neyman <stilor@....net>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Feng Tang <feng.tang@...el.com>,
	Yijing Wang <wangyijing@...wei.com>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] Fix coalescing host bridge windows in arch/x86/pci/acpi.c

[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@....net>
View attachment "acpi.c.diff" of type "text/x-patch" (723 bytes)