[PATCH v2 04/16] arm64: Downgrade flush_icache_range to invalidate

[Mark Rutland]

On Mon, May 17, 2021 at 08:51:12AM +0100, Fuad Tabba wrote:
> Since __flush_dcache_area is called right before,
> invalidate_icache_range is sufficient in this case.
> 
> Rewrite the comment to better explain the rationale behind the
> cache maintenance operations used here.
> 
> No functional change intended.
> Possible performance impact due to invalidating only the icache
> rather than invalidating and cleaning both caches.
> 
> Reported-by: Catalin Marinas <catalin.marinas at arm.com>
> Reported-by: Will Deacon <will at kernel.org>
> Link: https://lore.kernel.org/linux-arch/20200511110014.lb9PEahJ4hVOYrbwIb_qUHXyNy9KQzNFdb_I3YlzY6A@z/
> Signed-off-by: Fuad Tabba <tabba at google.com>
> ---
>  arch/arm64/kernel/machine_kexec.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c
> index 90a335c74442..ecd8915e02e1 100644
> --- a/arch/arm64/kernel/machine_kexec.c
> +++ b/arch/arm64/kernel/machine_kexec.c
> @@ -68,10 +68,14 @@ int machine_kexec_post_load(struct kimage *kimage)
>  	kimage->arch.kern_reloc = __pa(reloc_code);
>  	kexec_image_info(kimage);
>  
> -	/* Flush the reloc_code in preparation for its execution. */
> +	/*
> +	 * For execution with the MMU off and I-cache on, reloc_code needs to be
> +	 * cleaned to the PoC and invalidated from the I-cache.
> +	 */

Minor nit, but the I-cache is *always* on (SCTLR.I affects the
attributes used for fetches into the I-caches), so it would be slightly
better to drop the "and I-cache on" words.

Otherwise, this looks good to me.

Mark.

>  	__flush_dcache_area(reloc_code, arm64_relocate_new_kernel_size);
> -	flush_icache_range((uintptr_t)reloc_code, (uintptr_t)reloc_code +
> -			   arm64_relocate_new_kernel_size);
> +	invalidate_icache_range((uintptr_t)reloc_code,
> +				(uintptr_t)reloc_code +
> +					arm64_relocate_new_kernel_size);
>  
>  	return 0;
>  }
> -- 
> 2.31.1.751.gd2f1c929bd-goog
>