diff options
| author | Vasily Gorbik <gor@linux.vnet.ibm.com> | 2017-10-12 13:01:47 +0200 |
|---|---|---|
| committer | Martin Schwidefsky <schwidefsky@de.ibm.com> | 2017-10-18 14:11:29 +0200 |
| commit | 686140a1a9c41d85a4212a1c26d671139b76404b (patch) | |
| tree | 2d19e98601a9d9855f7eac6cca6cb364f5a9d650 /arch/s390/Kconfig | |
| parent | 76b3b62ade4baa13b270bafb96be730ebff913f0 (diff) | |
s390: introduce CPU alternatives
Implement CPU alternatives, which allows to optionally patch newer
instructions at runtime, based on CPU facilities availability.
A new kernel boot parameter "noaltinstr" disables patching.
Current implementation is derived from x86 alternatives. Although
ideal instructions padding (when altinstr is longer then oldinstr)
is added at compile time, and no oldinstr nops optimization has to be
done at runtime. Also couple of compile time sanity checks are done:
1. oldinstr and altinstr must be <= 254 bytes long,
2. oldinstr and altinstr must not have an odd length.
alternative(oldinstr, altinstr, facility);
alternative_2(oldinstr, altinstr1, facility1, altinstr2, facility2);
Both compile time and runtime padding consists of either 6/4/2 bytes nop
or a jump (brcl) + 2 bytes nop filler if padding is longer then 6 bytes.
.altinstructions and .altinstr_replacement sections are part of
__init_begin : __init_end region and are freed after initialization.
Signed-off-by: Vasily Gorbik <gor@linux.vnet.ibm.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 5fd4a67c93b3..080a3fcc3cb8 100644 --- a/arch/s390/Kconfig +++ b/arch/s390/Kconfig @@ -537,6 +537,22 @@ config ARCH_RANDOM If unsure, say Y. +config ALTERNATIVES + def_bool y + prompt "Patch optimized instructions for running CPU type" + help + When enabled the kernel code is compiled with additional + alternative instructions blocks optimized for newer CPU types. + These alternative instructions blocks are patched at kernel boot + time when running CPU supports them. This mechanism is used to + optimize some critical code paths (i.e. spinlocks) for newer CPUs + even if kernel is build to support older machine generations. + + This mechanism could be disabled by appending "noaltinstr" + option to the kernel command line. + + If unsure, say Y. + endmenu menu "Memory setup" @@ -811,6 +827,7 @@ config PFAULT config SHARED_KERNEL bool "VM shared kernel support" depends on !JUMP_LABEL + depends on !ALTERNATIVES help Select this option, if you want to share the text segment of the Linux kernel between different VM guests. This reduces memory |