linux-kernel - Re: [PATCH 1/3] arm64: clean up trampoline vector loads

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Date:   Tue, 17 Mar 2020 22:30:05 +0000
From:   Will Deacon <will@...nel.org>
To:     Rémi Denis-Courmont <remi@...lab.net>
Cc:     catalin.marinas@....com, linux-arm-kernel@...ts.infradead.org,
        mark.rutland@....com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] arm64: clean up trampoline vector loads

On Mon, Mar 16, 2020 at 02:40:44PM +0200, Rémi Denis-Courmont wrote:
> From: Rémi Denis-Courmont <remi.denis.courmont@...wei.com>
> 
> This switches from custom instruction patterns to the regular large
> memory model sequence with ADRP and LDR. In doing so, the ADD
> instruction can be eliminated in the SDEI handler, and the code no
> longer assumes that the trampoline vectors and the vectors address both
> start on a page boundary.
> 
> Signed-off-by: Rémi Denis-Courmont <remi.denis.courmont@...wei.com>
> ---
>  arch/arm64/kernel/entry.S | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index e5d4e30ee242..24f828739696 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -805,9 +805,9 @@ alternative_else_nop_endif
>  2:
>  	tramp_map_kernel	x30
>  #ifdef CONFIG_RANDOMIZE_BASE
> -	adr	x30, tramp_vectors + PAGE_SIZE
> +	adrp	x30, tramp_vectors + PAGE_SIZE
>  alternative_insn isb, nop, ARM64_WORKAROUND_QCOM_FALKOR_E1003
> -	ldr	x30, [x30]
> +	ldr	x30, [x30, #:lo12:__entry_tramp_data_start]
>  #else
>  	ldr	x30, =vectors
>  #endif
> @@ -953,9 +953,8 @@ SYM_CODE_START(__sdei_asm_entry_trampoline)
>  1:	str	x4, [x1, #(SDEI_EVENT_INTREGS + S_ORIG_ADDR_LIMIT)]
>  
>  #ifdef CONFIG_RANDOMIZE_BASE
> -	adr	x4, tramp_vectors + PAGE_SIZE
> -	add	x4, x4, #:lo12:__sdei_asm_trampoline_next_handler
> -	ldr	x4, [x4]
> +	adrp	x4, tramp_vectors + PAGE_SIZE
> +	ldr	x4, [x4, #:lo12:__sdei_asm_trampoline_next_handler]
>  #else
>  	ldr	x4, =__sdei_asm_handler
>  #endif

Acked-by: Will Deacon <will@...nel.org>

Will