问题说明：
用DEll R720服务器安装xen，kvm服务。创建好guest并启动，进入系统，系统运行都没问题，不过开机的时候发现一个failed提示，如下
Xen DomU启动中提示
# dmesg | grep PCI
PCI: Warning: Cannot find a gap in the 32bit address range
PCI: Unassigned devices with 32bit resource registers may break!
Allocating PCI resources starting at 400100000 (gap: 400100000:400000)
PCI-DMA: Using software bounce buffering for IO (SWIOTLB)
PCI: Fatal: No config space access function found
PCI: System does not support PCI
PCI: System does not support PCI
PCI: max bus depth: 0 pci_try_num: 1
pci_hotplug: PCI Hot Plug PCI Core version: 0.5
pciehp: PCI Express Hot Plug Controller Driver version: 0.4
acpiphp: ACPI Hot Plug PCI Controller Driver version: 0.5
# dmesg | grep ipmi
ipmi message handler version 39.2
IPMI System Interface driver.
ipmi_si: Adding default-specified kcs state machine
ipmi_si: Trying default-specified kcs state machine at i/o address 0xca2, slave address 0x0, irq 0
ipmi_si: Interface detection failed
ipmi_si: Adding default-specified smic state machine
ipmi_si: Trying default-specified smic state machine at i/o address 0xca9, slave address 0x0, irq 0
ipmi_si: Interface detection failed
ipmi_si: Adding default-specified bt state machine
ipmi_si: Trying default-specified bt state machine at i/o address 0xe4, slave address 0x0, irq 0
ipmi_si: Interface detection failed
ipmi_si: Unable to find any System Interface(s)
KVM guest启动中提示
ipmi message handler version 39.2
IPMI System Interface driver.
ipmi_si: Adding default-specified kcs state machine
ipmi_si: Trying default-specified kcs state machine at i/o address 0xca2, slave address 0x0, irq 0
ipmi_si: Interface detection failed
ipmi_si: Adding default-specified smic state machine
ipmi_si: Trying default-specified smic state machine at i/o address 0xca9, slave address 0x0, irq 0
ipmi_si: Interface detection failed
ipmi_si: Adding default-specified bt state machine
ipmi_si: Trying default-specified bt state machine at i/o address 0xe4, slave address 0x0, irq 0
ipmi_si: Interface detection failed
ipmi_si: Unable to find any System Interface(s)
因为这个问题查资料已经有半个月时间，各种谷歌搜，加入虚拟化群问，找不到答案，因为不影响使用，也曾多次纠结放弃查找问题，不过这块石头一直在心里放不下
······
直到刚看到红帽官方的文档，终于眼前一亮
kernelcomponentTypically, on platforms with no Intelligent Platform Management Interface (IPMI) hardware the user can see the following message the on the boot console and in dmesg log:
Could not set up I/O space
This message can be safely ignored, unless the system really does have IPMI hardware. In that case, the message indicates that the IPMI hardware could not be initialized. In order to support Advanced Configuration and Power Interface (ACPI) opregion access to IPMI functionality early in the boot, the IPMI driver has been statically linked with the kernel image. This means that the IPMI driver is "loaded" whether or not there is any hardware. The IPMI driver will try to initialize the IPMI hardware, but if there is no IPMI hardware present on the booting platform, the driver will print error messages on the console and in the dmesg log. Some of these error messages do not identify themselves as having been issued by the IPMI driver, so they can appear to be serious, when they are harmless.
如果不想看到此信息，可以在grub.conf的kernel最后加上ipmi_si.trydefaults=0参数，如下
default=0
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu
title CentOS (2.6.32-358.el6.x86_64)
root (hd0,0)
kernel /vmlinuz-2.6.32-358.el6.x86_64 ro root=/dev/mapper/VolGroup-lv_roo
ot rd_NO_LUKS LANG=en_US.UTF-8 rd_NO_MD console=hvc0 KEYTABLE=us rd_LVM_LV=VolGG
roup/lv_swap SYSFONT=latarcyrheb-sun16 crashkernel=auto rd_LVM_LV=VolGroup/lv_roo
ot rd_NO_DM rhgb quiet ipmi_si.trydefaults=0
initrd /initramfs-2.6.32-358.el6.x86_64.img
