ACRN Kernel Parameters

Generic Kernel Parameters

A number of kernel parameters control the behavior of ACRN-based systems. Some are applicable to the Service VM kernel, others to the User VM kernel, and some are applicable to both.

This section focuses on generic parameters from the Linux kernel which are relevant for configuring or debugging ACRN-based systems.

Parameter	Used in Service VM or User VM	Description	Usage Example
module_blacklist	Service VM	A comma-separated list of modules that should not be loaded. Useful to debug or work around issues related to specific modules.	module_blacklist=dwc3_pci
no_timer_check	Service VM, User VM	Disables the code that tests for broken timer IRQ sources.	no_timer_check
console	Service VM, User VM	Output console device and options. tty<n> Use the virtual console device <n>. ttyS<n>[,options] Use the specified serial port and options. Default options are 9600n8 meaning 9600 baud, no parity, 8 bits. Options are of the form bbbbpnf, where: bbbb is baud rate, for example, 9600 p is parity, one of n, o, or e (for none, odd, or even) n is number of bits (typically 8) f is flow control (r for RTS, or left blank) hvc<n> Use the hypervisor console device <n>. (This is for both Xen and PowerPC hypervisors.)	console=tty0 console=ttyS0 console=hvc0
loglevel	Service VM	All kernel messages with a loglevel less than the console loglevel will be printed to the console. The loglevel can also be changed with klogd or other programs. The loglevels are defined as follows: Loglevel Value Definition 0 (KERN_EMERG) System is unusable 1 (KERN_ALERT) Action must be taken immediately 2 (KERN_CRIT) Critical conditions 3 (KERN_ERR) Error conditions 4 (KERN_WARNING) Warning conditions 5 (KERN_NOTICE) Normal but significant condition 6 (KERN_INFO) Informational 7 (KERN_DEBUG) Debug-level messages	loglevel=7
ignore_loglevel	User VM	Ignoring loglevel setting will print all kernel messages to the console. Useful for debugging. We also add it as the printk module parameter, so users can change it dynamically, usually by changing /sys/module/printk/parameters/ignore_loglevel.	ignore_loglevel
log_buf_len	User VM	Sets the size of the printk ring buffer, in bytes. n must be a power of two and greater than the minimal size. The minimal size is defined by the LOG_BUF_SHIFT kernel config parameter. There is also the CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter that allows to increase the default size depending on the number of CPUs. See init/Kconfig for more details.	log_buf_len=16M
consoleblank	Service VM, User VM	The console blank (screen saver) timeout in seconds. Defaults to 600 (10 minutes). A value of 0 disables the blank timer.	consoleblank=0
rootwait	Service VM, User VM	Wait (indefinitely) for root device to show up. Useful for devices that are detected asynchronously (e.g., USB and MMC devices).	rootwait
root	Service VM, User VM	Define the root filesystem. /dev/<disk_name><decimal> represents the device number of the partition - device number of disk plus the partition number. /dev/<disk_name>p<decimal> same as above, this form is used when the disk name of the partitioned disk ends with a digit. To separate the disk name and partition slot, a p is inserted. PARTUUID=00112233-4455-6677-8899-AABBCCDDEEFF represents the unique ID of a partition if the partition table provides it. The UUID may be either an EFI/GPT UUID, or refer to an MSDOS partition using the format SSSSSSSS-PP, where SSSSSSSS is a zero-filled hexadecimal representation of the 32-bit NT disk signature, and PP is a zero-filled hexadecimal representation of the 1-based partition number.	root=/dev/mmcblk0p1 root=/dev/vda2 root=PARTUUID=00112233-4455-6677-8899-AABBCCDDEEFF
rw	Service VM, User VM	Mount the root device read/write on boot.	rw
tsc	User VM	Disable clocksource stability checks for TSC. Format: <string>, where the only supported value is: reliable: Mark TSC clocksource as reliable, and disable clocksource verification at runtime, and the stability checks done at boot. Used to enable high-resolution timer mode on older hardware, and in virtualized environments.	tsc=reliable
cma	Service VM	Sets the size of the kernel global memory area for contiguous memory allocations, and optionally the placement constraint by the physical address range of memory allocations. A value of 0 disables CMA altogether. For more information, see include/linux/dma-contiguous.	cma=64M@0
hvlog	Service VM	Sets the guest physical address and size of the dedicated hypervisor log ring buffer between the hypervisor and Service VM. A memmap parameter is also required to reserve the specified memory from the guest VM. If hypervisor relocation is disabled, verify that hv.MEMORY.HV_RAM_START and the hypervisor RAM size computed by the linker do not overlap with the hypervisor’s reserved buffer space allocated in the Service VM. Service VM GPA and HPA are a 1:1 mapping. If hypervisor relocation is enabled, reserve the memory below 256MB, since the hypervisor could be relocated anywhere between 256MB and 4GB. Enable address space layout randomization (ASLR) on the Service VM. This ensures that when the guest Linux is relocating the kernel image, it will avoid this buffer address.	hvlog=2M@0xe00000
memmap	Service VM	Mark specific memory as reserved. memmap=nn[KMG]$ss[KMG] Region of memory to be reserved is from ss to ss+nn, using K, M, and G representing kilobytes, megabytes, and gigabytes, respectively.	memmap=0x400000$0xa00000
ramoops.mem_address ramoops.mem_size ramoops.console_size	Service VM	Ramoops is an oops/panic logger that writes its logs to RAM before the system crashes. Ramoops uses a predefined memory area to store the dump. See Linux Kernel Ramoops oops/panic logger for details. This buffer should not overlap with hypervisor reserved memory and guest kernel image. See hvlog.	ramoops.mem_address=0xa00000 ramoops.mem_size=0x400000 ramoops.console_size=0x200000
reboot_panic	Service VM	Reboot in case of panic. The comma-delimited parameters are: reboot_mode: w (warm), s (soft), c (cold), or g (GPIO) reboot_type: b (BIOS), a (ACPI), k (kbd), t (triple), e (EFI), or p (PCI) reboot_cpu: s### (SMP, and processor number to be used for rebooting) reboot_force: f (force), or not specified.	reboot_panic=p,w
maxcpus	User VM	Maximum number of processors that an SMP kernel will bring up during boot. maxcpus=n where n >= 0 limits the kernel to bring up n processors during system boot. Giving n=0 is a special case, equivalent to nosmp, which also disables the I/O APIC. After booting, you can bring up additional plugged CPUs by executing echo 1 > /sys/devices/system/cpu/cpuX/online	maxcpus=1
nohpet	User VM	Don’t use the HPET timer.	nohpet
intel_iommu	User VM	Intel IOMMU driver (DMAR) option on: Enable Intel IOMMU driver. off: Disable Intel IOMMU driver. igfx_off: By default, gfx is mapped as a normal device. If a gfx device has a dedicated DMAR unit, the DMAR unit is bypassed by not enabling DMAR with this option. In this case, the gfx device will use the physical address for DMA.	intel_iommu=off
hugepages hugepagesz	Service VM, User VM	hugepages: HugeTLB pages to allocate at boot. hugepagesz: The size of the HugeTLB pages. On x86-64 and PowerPC, this option can be specified multiple times interleaved with hugepages to reserve huge pages of different sizes. Valid page sizes on x86-64 are 2M (when the CPU supports Page Size Extension (PSE)) and 1G (when the CPU supports the pdpe1gb cpuinfo flag).	hugepages=10 hugepagesz=1G
i915.modeset	Service VM	GPU driver loading option. 0: Disable the GPU driver loading for Intel GPU device. 1: Enable the GPU driver loading for Intel GPU device.	i915.modeset=0

Note

The hugepages and hugepagesz parameters are automatically taken care of by the ACRN Configurator tool. If users have customized hugepage settings to satisfy their particular workloads in the Service VM, the hugepages and hugepagesz parameters can be redefined in the GRUB menu to override the settings from the ACRN Configurator tool.