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| author | Martin Schwidefsky | 2018-01-16 07:11:45 +0100 |
|---|---|---|
| committer | Martin Schwidefsky | 2018-02-05 13:49:17 +0100 |
| commit | d768bd892fc8f066cd3aa000eb1867bcf32db0ee (patch) | |
| tree | 73856bebc552b175d71bef6859824d7ca8d8e051 /arch/s390/Kconfig | |
| parent | s390/alternative: use a copy of the facility bit mask (diff) | |
| download | kernel-qcow2-linux-d768bd892fc8f066cd3aa000eb1867bcf32db0ee.tar.gz kernel-qcow2-linux-d768bd892fc8f066cd3aa000eb1867bcf32db0ee.tar.xz kernel-qcow2-linux-d768bd892fc8f066cd3aa000eb1867bcf32db0ee.zip | |
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/Kconfig | 17 |
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" |