linux-kernel - Re: [PATCH v1 1/3] arm64: add a macro for SError synchronization

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Date:   Wed, 1 Nov 2017 11:24:59 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Dongjiu Geng <gengdongjiu@...wei.com>, catalin.marinas@....com,
        will.deacon@....com, marc.zyngier@....com,
        christoffer.dall@...aro.org, james.morse@....com,
        mark.rutland@....com, ard.biesheuvel@...aro.org,
        cov@...eaurora.org, Dave.Martin@....com, suzuki.poulose@....com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kvmarm@...ts.cs.columbia.edu
Subject: Re: [PATCH v1 1/3] arm64: add a macro for SError synchronization

On 01/11/17 19:14, Dongjiu Geng wrote:
> ARMv8.2 adds a control bit to each SCTLR_ELx to insert implicit
> Error Synchronization Barrier(IESB) operations at exception handler entry
> and exit. But not all hardware platform which support RAS Extension
> can support IESB. So for this case, software needs to manually insert
> Error Synchronization Barrier(ESB) operations.
> 
> In this macros, if system supports RAS Extensdddon instead of IESB,
> it will insert an ESB instruction.
> 
> Signed-off-by: Dongjiu Geng <gengdongjiu@...wei.com>
> ---
>  arch/arm64/include/asm/assembler.h | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
> index d4c0adf..e6c79c4 100644
> --- a/arch/arm64/include/asm/assembler.h
> +++ b/arch/arm64/include/asm/assembler.h
> @@ -517,4 +517,13 @@
>  #endif
>  	.endm
>  
> +	.macro	error_synchronize
> +alternative_if ARM64_HAS_IESB
> +	b	1f
> +alternative_else_nop_endif
> +alternative_if ARM64_HAS_RAS_EXTN
> +	esb
> +alternative_else_nop_endif
> +1:
> +	.endm

Having a branch in here is pretty horrible, and furthermore using label
number 1 has a pretty high chance of subtly breaking code where this
macro is inserted.

Can we not somehow nest or combine the alternative conditions here?

Robin.

>  #endif	/* __ASM_ASSEMBLER_H */
>