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c852f32058
The CP15 barrier instructions (CP15ISB, CP15DSB and CP15DMB) are deprecated in the ARMv7 architecture, superseded by ISB, DSB and DMB instructions respectively. Some implementations may provide the ability to disable the CP15 barriers by disabling the CP15BEN bit in SCTLR_EL1. If not enabled, the encodings for these instructions become undefined. To support legacy software using these instructions, this patch register hooks to - * emulate CP15 barriers and warn the user about their use * toggle CP15BEN in SCTLR_EL1 Signed-off-by: Punit Agrawal <punit.agrawal@arm.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Signed-off-by: Will Deacon <will.deacon@arm.com>
46 lines
1.6 KiB
Plaintext
46 lines
1.6 KiB
Plaintext
The arm64 port of the Linux kernel provides infrastructure to support
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emulation of instructions which have been deprecated, or obsoleted in
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the architecture. The infrastructure code uses undefined instruction
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hooks to support emulation. Where available it also allows turning on
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the instruction execution in hardware.
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The emulation mode can be controlled by writing to sysctl nodes
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(/proc/sys/abi). The following explains the different execution
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behaviours and the corresponding values of the sysctl nodes -
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* Undef
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Value: 0
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Generates undefined instruction abort. Default for instructions that
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have been obsoleted in the architecture, e.g., SWP
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* Emulate
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Value: 1
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Uses software emulation. To aid migration of software, in this mode
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usage of emulated instruction is traced as well as rate limited
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warnings are issued. This is the default for deprecated
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instructions, .e.g., CP15 barriers
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* Hardware Execution
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Value: 2
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Although marked as deprecated, some implementations may support the
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enabling/disabling of hardware support for the execution of these
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instructions. Using hardware execution generally provides better
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performance, but at the loss of ability to gather runtime statistics
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about the use of the deprecated instructions.
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The default mode depends on the status of the instruction in the
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architecture. Deprecated instructions should default to emulation
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while obsolete instructions must be undefined by default.
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Supported legacy instructions
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-----------------------------
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* SWP{B}
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Node: /proc/sys/abi/swp
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Status: Obsolete
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Default: Undef (0)
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* CP15 Barriers
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Node: /proc/sys/abi/cp15_barrier
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Status: Deprecated
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Default: Emulate (1)
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