Citrix XenServer – Intel 55×0 Chipset Errata – Interrupt Remapping Issue

has published a Knowledge Base article regarding and an issue regarding Interrupt Remapping.

Intel 5500/5520/X58 chipset revision 0x13 has an errata (#47 and #53) which makes the IOMMU interrupt remapping unit unreliable. This erratum causes interruptions and the interrupt remapping invalidations become unresponsive.
Refer to the link in More Information for details about Intel errata.

XenServer versions newer than XS6.0 (Boston) are affected because this is when the IOMMU support was enabled by default in the Xen hypervisor.

The recommended workaround of Intel for the errata is to disable the Interrupt remapping feature itself.

To Determine if the host has the affected chipset run the following command in the XenServer console:

lspci –n | grep “8086:342e (rev 13)”

  • If the preceding command returns nothing, then the system is not affected.
  • If the preceding command returns a result, then the xen-dmesg should be examined to see if interrupt remapping is enabled using the following command:
    # grep “Interrupt Remapping” /var/log/xen-dmesg

If remapping is enabled, follow this workaround steps to disable the feature:

Prevent the BIOS from advertising the feature

Turn off any BIOS feature mentioning Interrupt remapping or Turn off IOMMU support. This is vendor specific and might not be available in all BIOS implementations.

Prevent Xen from using the feature

Add a Xen boot parameter “iommu=no-intremap” to the /boot/extlinux.conf (put it after the xen.gz for the active linux boot target label)
Example of edited /boot/extlinux.conf
label xe
# XenServer
kernel mboot.c32
append /boot/xen.gz iommu=no-intremap dom0_mem=752M lowmem_emergency_pool=1M crashkernel=128M@32M console= vga=mode-0x0311 — /boot/vmlinuz-2.6-xen root=LABEL=root-abcdef ro xencons=hvc console=hvc0 console=tty0 quiet vga=785 splash — /boot/initrd-2.6-xen.img

The following command adds it to the Xen boot parameters for you without having to manually edit the /boot/extlinux.conf file:

/opt/xensource/libexec/xen-cmdline –set-xen iommu=no-intremap

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