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s390: add options to change branch prediction behaviour for the kernel

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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>
This commit is contained in:
Martin Schwidefsky
2018-01-16 07:11:45 +01:00
parent cf14899846
commit d768bd892f
7 changed files with 94 additions and 0 deletions
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arch/s390/kernel/early.c
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@@ -196,6 +196,8 @@ static noinline __init void setup_facility_list(void)
memcpy(S390_lowcore.alt_stfle_fac_list,
S390_lowcore.stfle_fac_list,
sizeof(S390_lowcore.alt_stfle_fac_list));
if (!IS_ENABLED(CONFIG_KERNEL_NOBP))
__clear_facility(82, S390_lowcore.alt_stfle_fac_list);
}
static __init void detect_diag9c(void)