What is IOMMU; How to check IOMMU is enabled?

What is IOMMU in Linux?

IOMMU (Input/Output Memory Management Unit) is a feature of modern CPUs that allows the operating system to map physical and virtual memory addresses to manage resources efficiently. IOMMU on Linux provides extra protection for a computer system by allowing the CPU to control direct memory access requests from devices such as USB, network, and storage controllers. This can help prevent malicious code from being injected into the computer's memory.

The IOMMU can be particularly useful in virtualization environments where multiple virtual machines (VMs) share the same physical hardware. It allows each VM to have its own virtual address space, preventing one VM from accessing the memory of another VM or the host system.

In addition, IOMMU can also help to prevent buffer overflow attacks and other security threats by allowing devices to access only the memory regions that are explicitly allocated to them.

It also helps to improve system performance by allowing multiple devices to share a single physical address space. IOMMU is enabled in most modern Linux distributions by default and can be managed through the kernel command line or configuration tools such as grub.conf. It is important to note that IOMMU does not guarantee security; however, it can provide an additional layer of protection for your system.

How to check if IOMMU is enabled?

There are various ways you can check if IOMMU is enabled in your system.

1) You can use the command line tool dmesg to check the boot messages. This will show you if IOMMU is enabled or not. Run the following command in a Linux terminal:

sudo dmesg | grep -e DMAR -e IOMMU

If you see any output with the words "DMAR" or "IOMMU," then it's likely that your system has IOMMU enabled. You can also check your BIOS settings to see if there is an option to enable or disable IOMMU.

2) You can also run the cat /proc/cmdline command to check the boot parameters. If you find iommu=on in the output, it confirms that IOMMU is enabled.

Output:

BOOT_IMAGE=(hd1,gpt3)/ostree/rhcos-ef525bbbe31830e8c37455b1f7f8c99cddc64cdfa01ce4b157fa1813eedd0f9a/vmlinuz-4.18.0-305.62.1.el8_4.x86_64 random.trust_cpu=on console=tty0 console=ttyS0,115200n8 ignition.platform.id=metal ostree=/ostree/boot.0/rhcos/ef525bbbe31830e8c37455b1f7f8c99cddc64cdfa01ce4b157fa1813eedd0f9a/0 root=UUID=e6910d2d-b242-42a7-bc4f-95c9912f527a rw rootflags=prjquota intel_iommu=on iommu=pt default_hugepagesz=1G hugepagesz=1G hugepages=128 transparent_hugepage=madvise

3) You can also search for a folder named /sys/kernel/iommu_groups in your file system. If the folder exists, it means that IOMMU is enabled on

ls /sys/kernel/iommu_groups/

Output:

0  103 109 114 12 125 130 136   141 147 152 158 163 169 174 18  19 24   3  35   40 46   51 57   62 68   73 79   84 9    95
1  104 11  115 120 126 131 137  142 148 153 159 164 17  175 180 2  25   30 36   41 47   52 58   63 69   74 8    85 90   96
10  105 110 116 121 127 132 138 143 149 154 16  165 170 176 181 20 26   31 37   42 48   53 59   64 7    75 80   86 91   97
100 106 111 117 122 128 133 139 144 15  155 160 166 171 177 182 21 27   32 38   43 49   54 6    65 70   76 81   87 92   98
101 107 112 118 123 129 134 14  145 150 156 161 167 172 178 183 22 28   33 39   44 5    55 60   66 71   77 82   88 93   99
102 108 113 119 124 13  135 140 146 151 157 162 168 173 179 184 23 29   34 4    45 50   56 61   67 72   78 83   89 94