From system dmesg:

[    0.000000] Intel-IOMMU: enabled

From xm dmesg:

(XEN) VMX: Supported advanced features:
(XEN)  - APIC MMIO access virtualisation
(XEN)  - APIC TPR shadow
(XEN)  - Virtual NMI
(XEN)  - MSR direct-access bitmap
(XEN) HVM: ASIDs disabled.
(XEN) HVM: VMX enabled
(XEN) I/O virtualisation disabled

=== WITH iommu=verbose ===


root@amsterdam-xen:~# xm dmesg
(XEN) Xen version 4.0.1 (Debian 4.0.1-2) (waldi@debian.org) (gcc version 4.4.5 (Debian 4.4.5-10) ) Wed Jan 12 14:04:06 UTC 2011
(XEN) Bootloader: GRUB 1.98+20100804-14
(XEN) Command line: placeholder iommu=verbose
(XEN) Video information:
(XEN)  VGA is text mode 80x25, font 8x16
(XEN)  VBE/DDC methods: V2; EDID transfer time: 1 seconds
(XEN) Disc information:
(XEN)  Found 2 MBR signatures
(XEN)  Found 2 EDD information structures
(XEN) Xen-e820 RAM map:
(XEN)  0000000000000000 - 000000000009e000 (usable)
(XEN)  000000000009e000 - 00000000000a0000 (reserved)
(XEN)  00000000000e0000 - 0000000000100000 (reserved)
(XEN)  0000000000100000 - 00000000cd362000 (usable)
(XEN)  00000000cd362000 - 00000000cd4a3000 (ACPI NVS)
(XEN)  00000000cd4a3000 - 00000000cfd5c000 (usable)
(XEN)  00000000cfd5c000 - 00000000cfd5e000 (reserved)
(XEN)  00000000cfd5e000 - 00000000cfe6e000 (usable)
(XEN)  00000000cfe6e000 - 00000000cfee5000 (ACPI NVS)
(XEN)  00000000cfee5000 - 00000000cfee8000 (usable)
(XEN)  00000000cfee8000 - 00000000cfef3000 (ACPI data)
(XEN)  00000000cfef3000 - 00000000cfef4000 (usable)
(XEN)  00000000cfef4000 - 00000000cfeff000 (ACPI data)
(XEN)  00000000cfeff000 - 00000000cff00000 (usable)
(XEN)  00000000cff00000 - 00000000d0000000 (reserved)
(XEN)  00000000f0000000 - 00000000f8000000 (reserved)
(XEN)  00000000fff00000 - 0000000100000000 (reserved)
(XEN)  0000000100000000 - 000000022c000000 (usable)
(XEN) ACPI: RSDP 000FE020, 0014 (r0 INTEL )
(XEN) ACPI: RSDT CFEFD038, 0064 (r1 INTEL  DG33TL        23C       1000013)
(XEN) ACPI: FACP CFEFC000, 0074 (r1 INTEL  DG33TL        23C MSFT  1000013)
(XEN) ACPI: DSDT CFEF8000, 3DE9 (r1 INTEL  DG33TL        23C MSFT  1000013)
(XEN) ACPI: FACS CFE79000, 0040
(XEN) ACPI: APIC CFEF7000, 0078 (r1 INTEL  DG33TL        23C MSFT  1000013)
(XEN) ACPI: WDDT CFEF6000, 0040 (r1 INTEL  DG33TL        23C MSFT  1000013)
(XEN) ACPI: MCFG CFEF5000, 003C (r1 INTEL  DG33TL        23C MSFT  1000013)
(XEN) ACPI: ASF! CFEF4000, 00A6 (r32 INTEL  DG33TL        23C MSFT  1000013)
(XEN) ACPI: ASPT CFEF2000, 0034 (r3 INTEL  DG33TL        23C MSFT  1000013)
(XEN) ACPI: WDTT CFEF1000, 02CC (r1 INTEL  DG33TL        23C MSFT  1000013)
(XEN) ACPI: SSDT CFEF0000, 0204 (r1 INTEL     CpuPm      23C MSFT  1000013)
(XEN) ACPI: SSDT CFEEF000, 01F9 (r1 INTEL   Cpu0Ist      23C MSFT  1000013)
(XEN) ACPI: SSDT CFEEE000, 01F9 (r1 INTEL   Cpu1Ist      23C MSFT  1000013)
(XEN) ACPI: SSDT CFEED000, 01F9 (r1 INTEL   Cpu2Ist      23C MSFT  1000013)
(XEN) ACPI: SSDT CFEEC000, 01F9 (r1 INTEL   Cpu3Ist      23C MSFT  1000013)
(XEN) ACPI: SSDT CFEEB000, 01CF (r1 INTEL   Cpu0Cst      23C MSFT  1000013)
(XEN) ACPI: SSDT CFEEA000, 01CF (r1 INTEL   Cpu1Cst      23C MSFT  1000013)
(XEN) ACPI: SSDT CFEE9000, 01CF (r1 INTEL   Cpu2Cst      23C MSFT  1000013)
(XEN) ACPI: SSDT CFEE8000, 01CF (r1 INTEL   Cpu3Cst      23C MSFT  1000013)
(XEN) System RAM: 8124MB (8319800kB)
(XEN) Domain heap initialised
(XEN) Processor #0 7:7 APIC version 20
(XEN) Processor #2 7:7 APIC version 20
(XEN) Processor #1 7:7 APIC version 20
(XEN) Processor #3 7:7 APIC version 20
(XEN) IOAPIC[0]: apic_id 2, version 32, address 0xfec00000, GSI 0-23
(XEN) Enabling APIC mode:  Flat.  Using 1 I/O APICs
(XEN) Using scheduler: SMP Credit Scheduler (credit)
(XEN) Detected 2992.604 MHz processor.
(XEN) Initing memory sharing.
(XEN) VMX: Supported advanced features:
(XEN)  - APIC MMIO access virtualisation
(XEN)  - APIC TPR shadow
(XEN)  - Virtual NMI
(XEN)  - MSR direct-access bitmap
(XEN) HVM: ASIDs disabled.
(XEN) HVM: VMX enabled
(XEN) I/O virtualisation disabled
(XEN) Total of 4 processors activated.
(XEN) ENABLING IO-APIC IRQs
(XEN)  -> Using new ACK method
(XEN) checking TSC synchronization across 4 CPUs: passed.
(XEN) Platform timer appears to have unexpectedly wrapped 10 or more times.
(XEN) Platform timer is 3.579MHz ACPI PM Timer
(XEN) Allocated console ring of 16 KiB.
(XEN) Brought up 4 CPUs
(XEN) CPUIDLE: disabled due to no HPET. Force enable with 'cpuidle'.
(XEN) *** LOADING DOMAIN 0 ***
(XEN)  Xen  kernel: 64-bit, lsb, compat32
(XEN)  Dom0 kernel: 64-bit, PAE, lsb, paddr 0x1000000 -> 0x16b8000
(XEN) PHYSICAL MEMORY ARRANGEMENT:
(XEN)  Dom0 alloc.:   0000000218000000->0000000220000000 (1989969 pages to be allocated)
(XEN) VIRTUAL MEMORY ARRANGEMENT:
(XEN)  Loaded kernel: ffffffff81000000->ffffffff816b8000
(XEN)  Init. ramdisk: ffffffff816b8000->ffffffff83239400
(XEN)  Phys-Mach map: ffffffff8323a000->ffffffff841a8a88
(XEN)  Start info:    ffffffff841a9000->ffffffff841a94b4
(XEN)  Page tables:   ffffffff841aa000->ffffffff841cf000
(XEN)  Boot stack:    ffffffff841cf000->ffffffff841d0000
(XEN)  TOTAL:         ffffffff80000000->ffffffff84400000
(XEN)  ENTRY ADDRESS: ffffffff81508200
(XEN) Dom0 has maximum 4 VCPUs
(XEN) Scrubbing Free RAM: .done.
(XEN) Xen trace buffers: disabled
(XEN) Std. Loglevel: Errors and warnings
(XEN) Guest Loglevel: Nothing (Rate-limited: Errors and warnings)
(XEN) Xen is relinquishing VGA console.
(XEN) *** Serial input -> DOM0 (type 'CTRL-a' three times to switch input to Xen)
(XEN) Freed 176kB init memory.