[PATCHv3 4/5] arm64: Emulate CP15 Barrier instructions

[Catalin Marinas]

On Mon, Oct 27, 2014 at 06:40:06PM +0000, Punit Agrawal wrote:
> diff --git a/Documentation/arm64/legacy_instructions.txt b/Documentation/arm64/legacy_instructions.txt
> index 5ab5861..a3b3da2 100644
> --- a/Documentation/arm64/legacy_instructions.txt
> +++ b/Documentation/arm64/legacy_instructions.txt
> @@ -38,3 +38,8 @@ Supported legacy instructions
>  Node: /proc/sys/abi/swp
>  Status: Obsolete
>  Default: Undef (0)
> +
> +* CP15 Barriers
> +Node: /proc/sys/abi/cp15_barrier
> +Status: Deprecated
> +Default: Emulate (1)
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 6ae8079..2f7026e 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -199,6 +199,21 @@ config SWP_EMULATION
>  
>  	  If unsure, say N
>  
> +config CP15_BARRIER_EMULATION
> +	bool "Emulate CP15 Barrier instructions"
> +	help
> +	  The CP15 barrier instructions - CP15ISB, CP15DSB, and
> +	  CP15DMB - are deprecated in ARMv8 (and ARMv7). It is
> +	  strongly recommended to use the ISB, DSB, and DMB
> +	  instructions instead.
> +
> +	  Say Y here to enable software emulation of these
> +	  instructions for AArch32 userspace code. When this option is
> +	  enabled, CP15 barrier usage is traced which can help
> +	  identify software that needs updating.
> +
> +	  If unsure, say N
> +
>  endif

default y (I think we had a discussion in private whether deprecated
should default to y and obsolete to y or n but I don't remember the
conclusion; it's worth adding it to the Documentation/ file).

> +#define SCTLR_EL1_CP15BEN (1 << 5)
> +
> +static inline void config_sctlr_el1(u32 clear, u32 set)
> +{
> +	u32 val;
> +
> +	asm volatile("mrs %0, sctlr_el1" : "=r" (val));
> +	val &= ~clear;
> +	val |= set;
> +	asm volatile("msr sctlr_el1, %0" : : "r" (val));
> +}
> +
> +static void enable_cp15_ben(void *info)
> +{
> +	config_sctlr_el1(0, SCTLR_EL1_CP15BEN);
> +}
> +
> +static void disable_cp15_ben(void *info)
> +{
> +	config_sctlr_el1(SCTLR_EL1_CP15BEN, 0);
> +}
> +
> +static int cpu_hotplug_notify(struct notifier_block *b, unsigned long action,
> +			  void *hcpu)
> +{
> +	switch (action) {
> +	case CPU_STARTING:
> +		enable_cp15_ben(NULL);
> +		return NOTIFY_DONE;
> +	}
> +
> +	return NOTIFY_OK;
> +}

Do we need CPU_STARTING_FROZEN as well?

This code always enables the CP15 barriers in hardware but it should
take into account the actual state (emulation, undef).

-- 
Catalin