PCI: boot parameter to avoid expansion ROM memory allocation

Contention for scarce PCI memory resources has been growing
due to an increasing number of PCI slots in large multi-node
systems.  The kernel currently attempts by default to
allocate memory for all PCI expansion ROMs so there has
also been an increasing number of PCI memory allocation
failures seen on these systems.  This occurs because the
BIOS either (1) provides insufficient PCI memory resource
for all the expansion ROMs or (2) provides adequate PCI
memory resource for expansion ROMs but provides the
space in kernel unexpected BIOS assigned P2P non-prefetch
windows.

The resulting PCI memory allocation failures may be benign
when related to memory requests for expansion ROMs themselves
but in some cases they can occur when attempting to allocate
space for more critical BARs.  This can happen when a successful
expansion ROM allocation request consumes memory resource
that was intended for a non-ROM BAR.  We have seen this
happen during PCI hotplug of an adapter that contains a
P2P bridge where successful memory allocation for an
expansion ROM BAR on device behind the bridge consumed
memory that was intended for a non-ROM BAR on the P2P bridge.
In all cases the allocation failure messages can be very
confusing for users.

This patch provides a new 'pci=norom' kernel boot parameter
that can be used to disable the default PCI expansion ROM memory
resource allocation.  This provides a way to avoid the above
described issues on systems that do not contain PCI devices
for which drivers or user-level applications depend on the
default PCI expansion ROM memory resource allocation behavior.

Signed-off-by: Gary Hade <garyhade@us.ibm.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index e07c432c731..9cf7b34f2db 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1496,6 +1496,9 @@ and is between 256 and 4096 characters. It is defined in the file
 				Use with caution as certain devices share
 				address decoders between ROMs and other
 				resources.
+		norom		[X86-32,X86_64] Do not assign address space to
+				expansion ROMs that do not already have
+				BIOS assigned address ranges.
 		irqmask=0xMMMM	[X86-32] Set a bit mask of IRQs allowed to be
 				assigned automatically to PCI devices. You can
 				make the kernel exclude IRQs of your ISA cards