summaryrefslogtreecommitdiffstats
path: root/arch/s390/Kconfig
diff options
context:
space:
mode:
authorMartin Schwidefsky <schwidefsky@de.ibm.com>2018-01-16 07:11:45 +0100
committerMartin Schwidefsky <schwidefsky@de.ibm.com>2018-02-05 13:49:17 +0100
commitd768bd892fc8f066cd3aa000eb1867bcf32db0ee (patch)
tree73856bebc552b175d71bef6859824d7ca8d8e051 /arch/s390/Kconfig
parentcf1489984641369611556bf00c48f945c77bcf02 (diff)
downloadlinux-d768bd892fc8f066cd3aa000eb1867bcf32db0ee.tar.bz2
s390: add options to change branch prediction behaviour for the kernel
Add the PPA instruction to the system entry and exit path to switch the kernel to a different branch prediction behaviour. The instructions are added via CPU alternatives and can be disabled with the "nospec" or the "nobp=0" kernel parameter. If the default behaviour selected with CONFIG_KERNEL_NOBP is set to "n" then the "nobp=1" parameter can be used to enable the changed kernel branch prediction. Acked-by: Cornelia Huck <cohuck@redhat.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Diffstat (limited to 'arch/s390/Kconfig')
-rw-r--r--arch/s390/Kconfig17
1 files changed, 17 insertions, 0 deletions
diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 0105ce28e246..d514e25095c2 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -540,6 +540,23 @@ config ARCH_RANDOM
If unsure, say Y.
+config KERNEL_NOBP
+ def_bool n
+ prompt "Enable modified branch prediction for the kernel by default"
+ help
+ If this option is selected the kernel will switch to a modified
+ branch prediction mode if the firmware interface is available.
+ The modified branch prediction mode improves the behaviour in
+ regard to speculative execution.
+
+ With the option enabled the kernel parameter "nobp=0" or "nospec"
+ can be used to run the kernel in the normal branch prediction mode.
+
+ With the option disabled the modified branch prediction mode is
+ enabled with the "nobp=1" kernel parameter.
+
+ If unsure, say N.
+
endmenu
menu "Memory setup"