[PATCH 1/2] arm64: Re-order reserved_ttbr0 in linker script

[Mark Rutland]

On Fri, Nov 17, 2017 at 11:41:42AM +0000, Steve Capper wrote:
> Currently one resolves the location of the reserved_ttbr0 for PAN by
> taking a positive offset from swapper_pg_dir. In a future patch we wish
> to extend the swapper s.t. its size is determined at link time rather
> than comile time, rendering SWAPPER_DIR_SIZE unsuitable for such a low
> level calculation.
> 
> In this patch we re-arrange the order of the linker script s.t. instead
> one computes reserved_ttbr0 by subtracting RESERVED_TTBR0_SIZE from
> swapper_pg_dir.
> 
> Signed-off-by: Steve Capper <steve.capper at arm.com>

Looks sane to me. FWIW:

Acked-by: Mark Rutland <mark.rutland at arm.com>

Mark.

> ---
>  arch/arm64/include/asm/asm-uaccess.h | 6 +++---
>  arch/arm64/include/asm/uaccess.h     | 2 +-
>  arch/arm64/kernel/vmlinux.lds.S      | 5 ++---
>  3 files changed, 6 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/asm-uaccess.h b/arch/arm64/include/asm/asm-uaccess.h
> index ecd9788cd298..95ba9865826a 100644
> --- a/arch/arm64/include/asm/asm-uaccess.h
> +++ b/arch/arm64/include/asm/asm-uaccess.h
> @@ -11,9 +11,9 @@
>   */
>  #ifdef CONFIG_ARM64_SW_TTBR0_PAN
>  	.macro	__uaccess_ttbr0_disable, tmp1
> -	mrs	\tmp1, ttbr1_el1		// swapper_pg_dir
> -	add	\tmp1, \tmp1, #SWAPPER_DIR_SIZE	// reserved_ttbr0 at the end of swapper_pg_dir
> -	msr	ttbr0_el1, \tmp1		// set reserved TTBR0_EL1
> +	mrs	\tmp1, ttbr1_el1			// swapper_pg_dir
> +	sub	\tmp1, \tmp1, #RESERVED_TTBR0_SIZE	// reserved_ttbr0 just before swapper_pg_dir
> +	msr	ttbr0_el1, \tmp1			// set reserved TTBR0_EL1
>  	isb
>  	.endm
>  
> diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
> index fc0f9eb66039..66170fd4b58f 100644
> --- a/arch/arm64/include/asm/uaccess.h
> +++ b/arch/arm64/include/asm/uaccess.h
> @@ -108,7 +108,7 @@ static inline void __uaccess_ttbr0_disable(void)
>  	unsigned long ttbr;
>  
>  	/* reserved_ttbr0 placed at the end of swapper_pg_dir */
> -	ttbr = read_sysreg(ttbr1_el1) + SWAPPER_DIR_SIZE;
> +	ttbr = read_sysreg(ttbr1_el1) - RESERVED_TTBR0_SIZE;
>  	write_sysreg(ttbr, ttbr0_el1);
>  	isb();
>  }
> diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
> index fe56c268a7d9..6aa717582f6f 100644
> --- a/arch/arm64/kernel/vmlinux.lds.S
> +++ b/arch/arm64/kernel/vmlinux.lds.S
> @@ -205,13 +205,12 @@ SECTIONS
>  	. = ALIGN(PAGE_SIZE);
>  	idmap_pg_dir = .;
>  	. += IDMAP_DIR_SIZE;
> -	swapper_pg_dir = .;
> -	. += SWAPPER_DIR_SIZE;
> -
>  #ifdef CONFIG_ARM64_SW_TTBR0_PAN
>  	reserved_ttbr0 = .;
>  	. += RESERVED_TTBR0_SIZE;
>  #endif
> +	swapper_pg_dir = .;
> +	. += SWAPPER_DIR_SIZE;
>  
>  	__pecoff_data_size = ABSOLUTE(. - __initdata_begin);
>  	_end = .;
> -- 
> 2.11.0
> 
> 
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