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Merge branch 'linus' into perf/urgent, to pick up the upstream merged…
… bits Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Original file line number | Diff line number | Diff line change |
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The arm64 port of the Linux kernel provides infrastructure to support | ||
emulation of instructions which have been deprecated, or obsoleted in | ||
the architecture. The infrastructure code uses undefined instruction | ||
hooks to support emulation. Where available it also allows turning on | ||
the instruction execution in hardware. | ||
|
||
The emulation mode can be controlled by writing to sysctl nodes | ||
(/proc/sys/abi). The following explains the different execution | ||
behaviours and the corresponding values of the sysctl nodes - | ||
|
||
* Undef | ||
Value: 0 | ||
Generates undefined instruction abort. Default for instructions that | ||
have been obsoleted in the architecture, e.g., SWP | ||
|
||
* Emulate | ||
Value: 1 | ||
Uses software emulation. To aid migration of software, in this mode | ||
usage of emulated instruction is traced as well as rate limited | ||
warnings are issued. This is the default for deprecated | ||
instructions, .e.g., CP15 barriers | ||
|
||
* Hardware Execution | ||
Value: 2 | ||
Although marked as deprecated, some implementations may support the | ||
enabling/disabling of hardware support for the execution of these | ||
instructions. Using hardware execution generally provides better | ||
performance, but at the loss of ability to gather runtime statistics | ||
about the use of the deprecated instructions. | ||
|
||
The default mode depends on the status of the instruction in the | ||
architecture. Deprecated instructions should default to emulation | ||
while obsolete instructions must be undefined by default. | ||
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||
Supported legacy instructions | ||
----------------------------- | ||
* SWP{B} | ||
Node: /proc/sys/abi/swp | ||
Status: Obsolete | ||
Default: Undef (0) | ||
|
||
* CP15 Barriers | ||
Node: /proc/sys/abi/cp15_barrier | ||
Status: Deprecated | ||
Default: Emulate (1) |
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