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author | Martin Schwidefsky <schwidefsky@de.ibm.com> | 2018-01-16 07:11:45 +0100 |
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committer | Martin Schwidefsky <schwidefsky@de.ibm.com> | 2018-02-05 13:49:17 +0100 |
commit | d768bd892fc8f066cd3aa000eb1867bcf32db0ee (patch) | |
tree | 73856bebc552b175d71bef6859824d7ca8d8e051 /arch/s390/kernel/alternative.c | |
parent | cf1489984641369611556bf00c48f945c77bcf02 (diff) | |
download | linux-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/kernel/alternative.c')
-rw-r--r-- | arch/s390/kernel/alternative.c | 23 |
1 files changed, 23 insertions, 0 deletions
diff --git a/arch/s390/kernel/alternative.c b/arch/s390/kernel/alternative.c index 1abf4f35d059..22476135f738 100644 --- a/arch/s390/kernel/alternative.c +++ b/arch/s390/kernel/alternative.c @@ -15,6 +15,29 @@ static int __init disable_alternative_instructions(char *str) early_param("noaltinstr", disable_alternative_instructions); +static int __init nobp_setup_early(char *str) +{ + bool enabled; + int rc; + + rc = kstrtobool(str, &enabled); + if (rc) + return rc; + if (enabled && test_facility(82)) + __set_facility(82, S390_lowcore.alt_stfle_fac_list); + else + __clear_facility(82, S390_lowcore.alt_stfle_fac_list); + return 0; +} +early_param("nobp", nobp_setup_early); + +static int __init nospec_setup_early(char *str) +{ + __clear_facility(82, S390_lowcore.alt_stfle_fac_list); + return 0; +} +early_param("nospec", nospec_setup_early); + struct brcl_insn { u16 opc; s32 disp; |