linux-kernel - Re: [PATCH v2] ARM: mm: proc-macros: ensure *_tlb

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Date:   Wed, 29 Sep 2021 13:37:25 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Fangrui Song <maskray@...gle.com>,
        Peter Smith <peter.smith@....com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Richard Henderson <richard.henderson@...aro.org>,
        Russell King <linux@...linux.org.uk>,
        Dave Martin <dave.martin@....com>,
        Nicolas Pitre <nico@...xnic.net>, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH v2] ARM: mm: proc-macros: ensure *_tlb_fns are 4B aligned

On Wed, Sep 29, 2021 at 12:20:24PM -0700, Nick Desaulniers wrote:
> QEMU 6.1.0 is more correct about trapping on misaligned accesses. A
> kernel built with CONFIG_THUMB2_KERNEL=y and using clang as the
> assembler could generate non-naturally-aligned v7wbi_tlb_fns which
> results in a boot failure. The original commit adding the macro missed
> the .align directive on this data.
> 
> Fixes: 66a625a88174 ("ARM: mm: proc-macros: Add generic proc/cache/tlb struct definition macros")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1447
> Link: https://lore.kernel.org/all/0699da7b-354f-aecc-a62f-e25693209af4@linaro.org/
> Debugged-by: Ard Biesheuvel <ardb@...nel.org>
> Debugged-by: Nathan Chancellor <nathan@...nel.org>
> Debugged-by: Richard Henderson <richard.henderson@...aro.org>
> Suggested-by: Ard Biesheuvel <ardb@...nel.org>
> Acked-by: Ard Biesheuvel <ardb@...nel.org>
> Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>

Tested-by: Nathan Chancellor <nathan@...nel.org>

> ---
> Changes V1 -> V2:
> * Drop accidentally committed Kconfig change.
> * Pick up Ard's AB tag.
> 
>  arch/arm/mm/proc-macros.S | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/arm/mm/proc-macros.S b/arch/arm/mm/proc-macros.S
> index e2c743aa2eb2..d9f7dfe2a7ed 100644
> --- a/arch/arm/mm/proc-macros.S
> +++ b/arch/arm/mm/proc-macros.S
> @@ -340,6 +340,7 @@ ENTRY(\name\()_cache_fns)
>  
>  .macro define_tlb_functions name:req, flags_up:req, flags_smp
>  	.type	\name\()_tlb_fns, #object
> +	.align 2
>  ENTRY(\name\()_tlb_fns)
>  	.long	\name\()_flush_user_tlb_range
>  	.long	\name\()_flush_kern_tlb_range
> 
> base-commit: 02d5e016800d082058b3d3b7c3ede136cdc6ddcb
> prerequisite-patch-id: 3edbe4a8485c7a75a61dbbe299e8ce1985d87ee0
> -- 
> 2.33.0.685.g46640cef36-goog
> 
>