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 which 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 printk module parameter, so users could 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 LOG_BUF_SHIFT kernel config parameter. There is also 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 disk name of the partitioned disk ends with a digit. To separate disk name and partition slot, a ‘p’ is inserted.
PARTUUID=00112233-4455-6677-8899-AABBCCDDEEFF: representing 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 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 disables 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 hv.MEMORY.HV_RAM_SIZE does 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 hypervisor could be relocated anywhere between 256MB and 4GB.

You should enable ASLR on SOS. This ensures that when guest Linux is relocating 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 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, gfx device will use 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

Note

The hugepages and hugepagesz parameters are automatically taken care of by ACRN config tool. In case user have customized hugepage settings to satisfy their particular workloads in Service VM, the hugepages and hugepagesz parameters could be redefined in GRUB menu to override the settings from ACRN config tool.

Intel GVT-g (AcrnGT) Parameters¶

This table gives an overview of all the Intel GVT-g parameters that are available to tweak the behavior of the graphics sharing (Intel GVT-g, aka AcrnGT) capabilities in ACRN. The GVT-g-kernel-options section below has more details on a few select parameters.

Parameter	Used in Service VM or User VM	Description	Usage example
i915.enable_gvt	Service VM	Enable Intel GVT-g graphics virtualization support in the host	i915.enable_gvt=1
i915.nuclear_pageflip	Service VM,User VM	Force enable atomic functionality on platforms that don’t have full support yet.	i915.nuclear_pageflip=1
i915.enable_guc	Service VM	Enable GuC load for HuC load.	i915.enable_guc=0x02
i915.enable_guc	User VM	Disable GuC	i915.enable_guc=0
i915.enable_hangcheck	User VM	Disable check GPU activity for detecting hangs.	i915.enable_hangcheck=0
i915.enable_fbc	User VM	Enable frame buffer compression for power savings	i915.enable_fbc=1

GVT-g (AcrnGT) Kernel Options Details¶

This section provides additional information and details on the kernel command line options that are related to AcrnGT.

i915.enable_gvt¶

This option enables support for Intel GVT-g graphics virtualization support in the host. By default, it’s not enabled, so we need to add i915.enable_gvt=1 in the Service VM kernel command line. This is a Service OS only parameter, and cannot be enabled in the User VM.

i915.enable_hangcheck¶

This parameter enable detection of a GPU hang. When enabled, the i915 will start a timer to check if the workload is completed in a specific time. If not, i915 will treat it as a GPU hang and trigger a GPU reset.

In AcrnGT, the workload in Service VM and User VM can be set to different priorities. If Service VM is assigned a higher priority than the User VM, the User VM’s workload might not be able to run on the HW on time. This may lead to the guest i915 triggering a hangcheck and lead to a guest GPU reset. This reset is unnecessary so we use i915.enable_hangcheck=0 to disable this timeout check and prevent guest from triggering unnecessary GPU resets.