linux-kernel - Re: [PATCH v3 19/20] arm64: mm: Introduce TTBR_ASID

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Date:   Wed, 6 Dec 2017 14:12:47 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Will Deacon <will.deacon@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        catalin.marinas@....com, ard.biesheuvel@...aro.org,
        sboyd@...eaurora.org, dave.hansen@...ux.intel.com,
        keescook@...omium.org, msalter@...hat.com, labbott@...hat.com,
        tglx@...utronix.de
Subject: Re: [PATCH v3 19/20] arm64: mm: Introduce TTBR_ASID_MASK for getting
 at the ASID in the TTBR

On Wed, Dec 06, 2017 at 12:35:38PM +0000, Will Deacon wrote:
> There are now a handful of open-coded masks to extract the ASID from a
> TTBR value, so introduce a TTBR_ASID_MASK and use that instead.
> 
> Suggested-by: Mark Rutland <mark.rutland@....com>
> Signed-off-by: Will Deacon <will.deacon@....com>

Thanks!

Reviewed-by: Mark Rutland <mark.rutland@....com>

Mark.

> ---
>  arch/arm64/include/asm/asm-uaccess.h | 3 ++-
>  arch/arm64/include/asm/mmu.h         | 1 +
>  arch/arm64/include/asm/uaccess.h     | 4 ++--
>  arch/arm64/kernel/entry.S            | 2 +-
>  4 files changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/asm-uaccess.h b/arch/arm64/include/asm/asm-uaccess.h
> index 21b8cf304028..f4f234b6155e 100644
> --- a/arch/arm64/include/asm/asm-uaccess.h
> +++ b/arch/arm64/include/asm/asm-uaccess.h
> @@ -4,6 +4,7 @@
>  
>  #include <asm/alternative.h>
>  #include <asm/kernel-pgtable.h>
> +#include <asm/mmu.h>
>  #include <asm/sysreg.h>
>  #include <asm/assembler.h>
>  
> @@ -17,7 +18,7 @@
>  	msr	ttbr0_el1, \tmp1		// set reserved TTBR0_EL1
>  	isb
>  	sub	\tmp1, \tmp1, #SWAPPER_DIR_SIZE
> -	bic	\tmp1, \tmp1, #(0xffff << 48)
> +	bic	\tmp1, \tmp1, #TTBR_ASID_MASK
>  	msr	ttbr1_el1, \tmp1		// set reserved ASID
>  	isb
>  	.endm
> diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h
> index da6f12e40714..6f7bdb89817f 100644
> --- a/arch/arm64/include/asm/mmu.h
> +++ b/arch/arm64/include/asm/mmu.h
> @@ -18,6 +18,7 @@
>  
>  #define MMCF_AARCH32	0x1	/* mm context flag for AArch32 executables */
>  #define USER_ASID_FLAG	(UL(1) << 48)
> +#define TTBR_ASID_MASK	(UL(0xffff) << 48)
>  
>  #ifndef __ASSEMBLY__
>  
> diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
> index 750a3b76a01c..6eadf55ebaf0 100644
> --- a/arch/arm64/include/asm/uaccess.h
> +++ b/arch/arm64/include/asm/uaccess.h
> @@ -112,7 +112,7 @@ static inline void __uaccess_ttbr0_disable(void)
>  	write_sysreg(ttbr + SWAPPER_DIR_SIZE, ttbr0_el1);
>  	isb();
>  	/* Set reserved ASID */
> -	ttbr &= ~(0xffffUL << 48);
> +	ttbr &= ~TTBR_ASID_MASK;
>  	write_sysreg(ttbr, ttbr1_el1);
>  	isb();
>  }
> @@ -131,7 +131,7 @@ static inline void __uaccess_ttbr0_enable(void)
>  
>  	/* Restore active ASID */
>  	ttbr1 = read_sysreg(ttbr1_el1);
> -	ttbr1 |= ttbr0 & (0xffffUL << 48);
> +	ttbr1 |= ttbr0 & TTBR_ASID_MASK;
>  	write_sysreg(ttbr1, ttbr1_el1);
>  	isb();
>  
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index 5d51bdbb2131..3eabcb194c87 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -205,7 +205,7 @@ alternative_else_nop_endif
>  
>  	.if	\el != 0
>  	mrs	x21, ttbr1_el1
> -	tst	x21, #0xffff << 48		// Check for the reserved ASID
> +	tst	x21, #TTBR_ASID_MASK		// Check for the reserved ASID
>  	orr	x23, x23, #PSR_PAN_BIT		// Set the emulated PAN in the saved SPSR
>  	b.eq	1f				// TTBR0 access already disabled
>  	and	x23, x23, #~PSR_PAN_BIT		// Clear the emulated PAN in the saved SPSR
> -- 
> 2.1.4
>