Merge branch 'x86-timers-for-linus' of git://git.kernel.org/pub/scm/linux/kernel...
[linux-2.6-microblaze.git] / Documentation / admin-guide / kernel-parameters.txt
index c4d8300..58e69ec 100644 (file)
                        upon panic. This parameter reserves the physical
                        memory region [offset, offset + size] for that kernel
                        image. If '@offset' is omitted, then a suitable offset
-                       is selected automatically. Check
-                       Documentation/kdump/kdump.txt for further details.
+                       is selected automatically.
+                       [KNL, x86_64] select a region under 4G first, and
+                       fall back to reserve region above 4G when '@offset'
+                       hasn't been specified.
+                       See Documentation/kdump/kdump.txt for further details.
 
        crashkernel=range1:size1[,range2:size2,...][@offset]
                        [KNL] Same as above, but depends on the memory
                        in the "bleeding edge" mini2440 support kernel at
                        http://repo.or.cz/w/linux-2.6/mini2440.git
 
+       mitigations=
+                       [X86,PPC,S390] Control optional mitigations for CPU
+                       vulnerabilities.  This is a set of curated,
+                       arch-independent options, each of which is an
+                       aggregation of existing arch-specific options.
+
+                       off
+                               Disable all optional CPU mitigations.  This
+                               improves system performance, but it may also
+                               expose users to several CPU vulnerabilities.
+                               Equivalent to: nopti [X86,PPC]
+                                              nospectre_v1 [PPC]
+                                              nobp=0 [S390]
+                                              nospectre_v2 [X86,PPC,S390]
+                                              spectre_v2_user=off [X86]
+                                              spec_store_bypass_disable=off [X86,PPC]
+                                              l1tf=off [X86]
+
+                       auto (default)
+                               Mitigate all CPU vulnerabilities, but leave SMT
+                               enabled, even if it's vulnerable.  This is for
+                               users who don't want to be surprised by SMT
+                               getting disabled across kernel upgrades, or who
+                               have other ways of avoiding SMT-based attacks.
+                               Equivalent to: (default behavior)
+
+                       auto,nosmt
+                               Mitigate all CPU vulnerabilities, disabling SMT
+                               if needed.  This is for users who always want to
+                               be fully mitigated, even if it means losing SMT.
+                               Equivalent to: l1tf=flush,nosmt [X86]
+
        mminit_loglevel=
                        [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
                        parameter allows control of the logging verbosity for
                                see CONFIG_RAS_CEC help text.
 
        rcu_nocbs=      [KNL]
-                       The argument is a cpu list, as described above.
+                       The argument is a cpu list, as described above,
+                       except that the string "all" can be used to
+                       specify every CPU on the system.
 
                        In kernels built with CONFIG_RCU_NOCB_CPU=y, set
                        the specified list of CPUs to be no-callback CPUs.