PCI: allow assignment of memory resources with a specified alignment

This patch allows memory resources to be assigned with a specified
alignment at boot-time or run-time. The patch is useful when we use PCI
pass-through, because page-aligned memory resources are required to
securely share PCI resources with guest drivers.

If you want to assign the resource at boot time, please set
"pci=resource_alignment=" boot parameter.

This is format of "pci=resource_alignment=" boot parameter:

        [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
                Specifies alignment and device to reassign
                aligned memory resources.
                If <order of align> is not specified, PAGE_SIZE is
                used as alignment.
                PCI-PCI bridge can be specified, if resource
                windows need to be expanded.

This is example:

        pci=resource_alignment=20@07:00.0;18@0f:00.0;00:1d.7

If you want to assign the resource at run-time, please set
"/sys/bus/pci/resource_alignment" file, and hot-remove the device and
hot-add the device.  For this purpose, fakephp or PCI hotplug interfaces
can be used.

The format of "/sys/bus/pci/resource_alignment" file is the same with
boot parameter. You can use "," instead of ";".

For example:

        # cd /sys/bus/pci
        # echo -n 20@12:00.0 > resource_alignment
        # echo 1 > devices/0000:12:00.0/remove
        # echo 1 > rescan

Reviewed-by: Alex Chiang <achiang@hp.com>
Reviewed-by: Yu Zhao <yu.zhao@intel.com>
Signed-off-by: Yuji Shimada <shimada-yxb@necst.nec.co.jp>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

1 files changed, 9 insertions, 0 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index c7c441e7930e..1754fedc531c 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1760,6 +1760,15 @@ and is between 256 and 4096 characters. It is defined in the file
                 cbmemsize=nn[KMG]       The fixed amount of bus space which is
                                 reserved for the CardBus bridge's memory
                                 window. The default value is 64 megabytes.
+                resource_alignment=
+                                Format:
+                                [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
+                                Specifies alignment and device to reassign
+                                aligned memory resources.
+                                If <order of align> is not specified,
+                                PAGE_SIZE is used as alignment.
+                                PCI-PCI bridge can be specified, if resource
+                                windows need to be expanded.
 
         pcie_aspm=      [PCIE] Forcibly enable or disable PCIe Active State Power
                         Management.