Merge tag 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/random
[sfrench/cifs-2.6.git] / Documentation / admin-guide / kernel-parameters.txt
index 227c5c6fa4c1792d36bcda67775111a8e358449f..64a3bf54b97492e3b2b25508a7785d1f1e9e4186 100644 (file)
                        Defaults to the default architecture's huge page size
                        if not specified.
 
+       deferred_probe_timeout=
+                       [KNL] Debugging option to set a timeout in seconds for
+                       deferred probe to give up waiting on dependencies to
+                       probe. Only specific dependencies (subsystems or
+                       drivers) that have opted in will be ignored. A timeout of 0
+                       will timeout at the end of initcalls. This option will also
+                       dump out devices still on the deferred probe list after
+                       retrying.
+
        dhash_entries=  [KNL]
                        Set number of hash buckets for dentry cache.
 
        disable=        [IPV6]
                        See Documentation/networking/ipv6.txt.
 
+       hardened_usercopy=
+                        [KNL] Under CONFIG_HARDENED_USERCOPY, whether
+                        hardening is enabled for this boot. Hardened
+                        usercopy checking is used to protect the kernel
+                        from reading or writing beyond known memory
+                        allocation boundaries as a proactive defense
+                        against bounds-checking flaws in the kernel's
+                        copy_to_user()/copy_from_user() interface.
+                on      Perform hardened usercopy checks (default).
+                off     Disable hardened usercopy checks.
+
        disable_radix   [PPC]
                        Disable RADIX MMU mode on POWER9
 
                merge
                nomerge
                soft
-               pt              [x86, IA-64]
+               pt              [x86]
+               nopt            [x86]
                nobypass        [PPC/POWERNV]
                        Disable IOMMU bypass, using IOMMU for PCI devices.
 
                        (virtualized real and unpaged mode) on capable
                        Intel chips. Default is 1 (enabled)
 
+       kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
+                       CVE-2018-3620.
+
+                       Valid arguments: never, cond, always
+
+                       always: L1D cache flush on every VMENTER.
+                       cond:   Flush L1D on VMENTER only when the code between
+                               VMEXIT and VMENTER can leak host memory.
+                       never:  Disables the mitigation
+
+                       Default is cond (do L1 cache flush in specific instances)
+
        kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
                        feature (tagged TLBs) on capable Intel chips.
                        Default is 1 (enabled)
 
+       l1tf=           [X86] Control mitigation of the L1TF vulnerability on
+                             affected CPUs
+
+                       The kernel PTE inversion protection is unconditionally
+                       enabled and cannot be disabled.
+
+                       full
+                               Provides all available mitigations for the
+                               L1TF vulnerability. Disables SMT and
+                               enables all mitigations in the
+                               hypervisors, i.e. unconditional L1D flush.
+
+                               SMT control and L1D flush control via the
+                               sysfs interface is still possible after
+                               boot.  Hypervisors will issue a warning
+                               when the first VM is started in a
+                               potentially insecure configuration,
+                               i.e. SMT enabled or L1D flush disabled.
+
+                       full,force
+                               Same as 'full', but disables SMT and L1D
+                               flush runtime control. Implies the
+                               'nosmt=force' command line option.
+                               (i.e. sysfs control of SMT is disabled.)
+
+                       flush
+                               Leaves SMT enabled and enables the default
+                               hypervisor mitigation, i.e. conditional
+                               L1D flush.
+
+                               SMT control and L1D flush control via the
+                               sysfs interface is still possible after
+                               boot.  Hypervisors will issue a warning
+                               when the first VM is started in a
+                               potentially insecure configuration,
+                               i.e. SMT enabled or L1D flush disabled.
+
+                       flush,nosmt
+
+                               Disables SMT and enables the default
+                               hypervisor mitigation.
+
+                               SMT control and L1D flush control via the
+                               sysfs interface is still possible after
+                               boot.  Hypervisors will issue a warning
+                               when the first VM is started in a
+                               potentially insecure configuration,
+                               i.e. SMT enabled or L1D flush disabled.
+
+                       flush,nowarn
+                               Same as 'flush', but hypervisors will not
+                               warn when a VM is started in a potentially
+                               insecure configuration.
+
+                       off
+                               Disables hypervisor mitigations and doesn't
+                               emit any warnings.
+
+                       Default is 'flush'.
+
+                       For details see: Documentation/admin-guide/l1tf.rst
+
        l2cr=           [PPC]
 
        l3cr=           [PPC]
        nosmt           [KNL,S390] Disable symmetric multithreading (SMT).
                        Equivalent to smt=1.
 
+                       [KNL,x86] Disable symmetric multithreading (SMT).
+                       nosmt=force: Force disable SMT, cannot be undone
+                                    via the sysfs control file.
+
+       nospectre_v1    [PPC] Disable mitigations for Spectre Variant 1 (bounds
+                       check bypass). With this option data leaks are possible
+                       in the system.
+
        nospectre_v2    [X86] Disable all mitigations for the Spectre variant 2
                        (indirect branch prediction) vulnerability. System may
                        allow data leaks with this option, which is equivalent
 
        nosync          [HW,M68K] Disables sync negotiation for all devices.
 
-       notsc           [BUGS=X86-32] Disable Time Stamp Counter
-
        nowatchdog      [KNL] Disable both lockup detectors, i.e.
                        soft-lockup and NMI watchdog (hard-lockup).
 
                        on: enable the feature
 
        page_poison=    [KNL] Boot-time parameter changing the state of
-                       poisoning on the buddy allocator.
-                       off: turn off poisoning
+                       poisoning on the buddy allocator, available with
+                       CONFIG_PAGE_POISONING=y.
+                       off: turn off poisoning (default)
                        on: turn on poisoning
 
        panic=          [KNL] Kernel behaviour on panic: delay <timeout>
                        See header of drivers/block/paride/pcd.c.
                        See also Documentation/blockdev/paride.txt.
 
-       pci=option[,option...]  [PCI] various PCI subsystem options:
-               earlydump       [X86] dump PCI config space before the kernel
+       pci=option[,option...]  [PCI] various PCI subsystem options.
+
+                               Some options herein operate on a specific device
+                               or a set of devices (<pci_dev>). These are
+                               specified in one of the following formats:
+
+                               [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
+                               pci:<vendor>:<device>[:<subvendor>:<subdevice>]
+
+                               Note: the first format specifies a PCI
+                               bus/device/function address which may change
+                               if new hardware is inserted, if motherboard
+                               firmware changes, or due to changes caused
+                               by other kernel parameters. If the
+                               domain is left unspecified, it is
+                               taken to be zero. Optionally, a path
+                               to a device through multiple device/function
+                               addresses can be specified after the base
+                               address (this is more robust against
+                               renumbering issues).  The second format
+                               selects devices using IDs from the
+                               configuration space which may match multiple
+                               devices in the system.
+
+               earlydump       dump PCI config space before the kernel
                                changes anything
                off             [X86] don't probe for the PCI bus
                bios            [X86-32] force use of PCI BIOS, don't access
                                window. The default value is 64 megabytes.
                resource_alignment=
                                Format:
-                               [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
-                               [<order of align>@]pci:<vendor>:<device>\
-                                               [:<subvendor>:<subdevice>][; ...]
+                               [<order of align>@]<pci_dev>[; ...]
                                Specifies alignment and device to reassign
-                               aligned memory resources.
+                               aligned memory resources. How to
+                               specify the device is described above.
                                If <order of align> is not specified,
                                PAGE_SIZE is used as alignment.
                                PCI-PCI bridge can be specified, if resource
                                Adding the window is slightly risky (it may
                                conflict with unreported devices), so this
                                taints the kernel.
+               disable_acs_redir=<pci_dev>[; ...]
+                               Specify one or more PCI devices (in the format
+                               specified above) separated by semicolons.
+                               Each device specified will have the PCI ACS
+                               redirect capabilities forced off which will
+                               allow P2P traffic between devices through
+                               bridges without forcing it upstream. Note:
+                               this removes isolation between devices and
+                               may put more devices in an IOMMU group.
 
        pcie_aspm=      [PCIE] Forcibly enable or disable PCIe Active State Power
                        Management.
                        Set time (s) after boot for CPU-hotplug testing.
 
        rcutorture.onoff_interval= [KNL]
-                       Set time (s) between CPU-hotplug operations, or
-                       zero to disable CPU-hotplug testing.
+                       Set time (jiffies) between CPU-hotplug operations,
+                       or zero to disable CPU-hotplug testing.
 
        rcutorture.shuffle_interval= [KNL]
                        Set task-shuffle interval (s).  Shuffling tasks
                        This parameter controls whether the Speculative Store
                        Bypass optimization is used.
 
+                       On x86 the options are:
+
                        on      - Unconditionally disable Speculative Store Bypass
                        off     - Unconditionally enable Speculative Store Bypass
                        auto    - Kernel detects whether the CPU model contains an
                        seccomp - Same as "prctl" above, but all seccomp threads
                                  will disable SSB unless they explicitly opt out.
 
-                       Not specifying this option is equivalent to
-                       spec_store_bypass_disable=auto.
-
                        Default mitigations:
                        X86:    If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
 
+                       On powerpc the options are:
+
+                       on,auto - On Power8 and Power9 insert a store-forwarding
+                                 barrier on kernel entry and exit. On Power7
+                                 perform a software flush on kernel entry and
+                                 exit.
+                       off     - No action.
+
+                       Not specifying this option is equivalent to
+                       spec_store_bypass_disable=auto.
+
        spia_io_base=   [HW,MTD]
        spia_fio_base=
        spia_pedr=
        xirc2ps_cs=     [NET,PCMCIA]
                        Format:
                        <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
+
+       xhci-hcd.quirks         [USB,KNL]
+                       A hex value specifying bitmask with supplemental xhci
+                       host controller quirks. Meaning of each bit can be
+                       consulted in header drivers/usb/host/xhci.h.