.. _kernel-parameters: 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. .. list-table:: :header-rows: 1 :widths: 10,10,50,30 * - 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`` Use the virtual console device . ``ttyS[,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`` Use the hypervisor console device . (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: .. list-table:: :header-rows: 1 * - 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/`` represents the device number of the partition - device number of disk plus the partition number ``/dev/p`` 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: , 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 :option:`hv.MEMORY.HV_RAM_START` and :option:`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 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. .. list-table:: :header-rows: 1 :widths: 10,10,50,30 * - 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-kernel-options: 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.