DMAR DRHD: handling fault status reg 102

After Proxmox Backup Server boot, system hangs with:

DMAR DRHD: handling fault status reg 102

nointremap  [X86-64, Intel-IOMMU] Do not enable interrupt remapping.
            [Deprecated - use intremap=off]

Apr 02 12:41:54 pbs2 kernel: DMAR-IR: Use 'intremap=no_x2apic_optout' to override the BIOS setting.
Apr 02 12:41:54 pbs2 kernel: DMAR-IR: Enabled IRQ remapping in xapic mode
Apr 02 12:41:54 pbs2 kernel: x2apic: IRQ remapping doesn't support X2APIC mode

Solution:

Add intremap=no_x2apic_optout or nointremap=off to kernel cmdline.