linux-kernel - Re: [PATCH v2 05/17] arm64: Helper for parange to PASize

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Date:   Thu, 26 Apr 2018 11:58:19 +0100
From:   Julien Grall <julien.grall@....com>
To:     Suzuki K Poulose <suzuki.poulose@....com>,
        linux-arm-kernel@...ts.infradead.org
Cc:     ard.biesheuvel@...aro.org, kvm@...r.kernel.org,
        marc.zyngier@....com, catalin.marinas@....com,
        punit.agrawal@....com, will.deacon@....com,
        linux-kernel@...r.kernel.org, kristina.martsenko@....com,
        pbonzini@...hat.com, kvmarm@...ts.cs.columbia.edu
Subject: Re: [PATCH v2 05/17] arm64: Helper for parange to PASize

Hi Suzuki,

On 27/03/18 14:15, Suzuki K Poulose wrote:
> Add a helper to convert ID_AA64MMFR0_EL1:PARange to they physical
> size shift. Limit the size to the maximum supported by the kernel.
> We are about to move the user of this code and this helps to
> keep the changes cleaner.

It is probably worth to mention that you are also adding 52-bit support 
in the patch.

Cheers,

> 
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will.deacon@....com>
> Cc: Marc Zyngier <marc.zyngier@....com>
> Cc: Christoffer Dall <cdall@...nel.org>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> ---
>   arch/arm64/include/asm/cpufeature.h | 16 ++++++++++++++++
>   arch/arm64/kvm/hyp/s2-setup.c       | 28 +++++-----------------------
>   2 files changed, 21 insertions(+), 23 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
> index fbf0aab..1f2a5dd 100644
> --- a/arch/arm64/include/asm/cpufeature.h
> +++ b/arch/arm64/include/asm/cpufeature.h
> @@ -311,6 +311,22 @@ static inline u64 read_zcr_features(void)
>   	return zcr;
>   }
>   
> +static inline u32 id_aa64mmfr0_parange_to_phys_shift(int parange)
> +{
> +	switch (parange) {
> +	case 0: return 32;
> +	case 1: return 36;
> +	case 2: return 40;
> +	case 3: return 42;
> +	case 4: return 44;
> +	/* Report 48 bit if the kernel doesn't support 52bit */
> +	default:
> +	case 5: return 48;
> +#ifdef CONFIG_ARM64_PA_BITS_52
> +	case 6: return 52;
> +#endif
> +	}
> +}
>   #endif /* __ASSEMBLY__ */
>   
>   #endif
> diff --git a/arch/arm64/kvm/hyp/s2-setup.c b/arch/arm64/kvm/hyp/s2-setup.c
> index 603e1ee..b1129c8 100644
> --- a/arch/arm64/kvm/hyp/s2-setup.c
> +++ b/arch/arm64/kvm/hyp/s2-setup.c
> @@ -19,11 +19,13 @@
>   #include <asm/kvm_arm.h>
>   #include <asm/kvm_asm.h>
>   #include <asm/kvm_hyp.h>
> +#include <asm/cpufeature.h>
>   
>   u32 __hyp_text __init_stage2_translation(void)
>   {
>   	u64 val = VTCR_EL2_FLAGS;
>   	u64 parange;
> +	u32 phys_shift;
>   	u64 tmp;
>   
>   	/*
> @@ -37,27 +39,7 @@ u32 __hyp_text __init_stage2_translation(void)
>   	val |= parange << 16;
>   
>   	/* Compute the actual PARange... */
> -	switch (parange) {
> -	case 0:
> -		parange = 32;
> -		break;
> -	case 1:
> -		parange = 36;
> -		break;
> -	case 2:
> -		parange = 40;
> -		break;
> -	case 3:
> -		parange = 42;
> -		break;
> -	case 4:
> -		parange = 44;
> -		break;
> -	case 5:
> -	default:
> -		parange = 48;
> -		break;
> -	}
> +	phys_shift = id_aa64mmfr0_parange_to_phys_shift(parange);
>   
>   	/*
>   	 * ... and clamp it to 40 bits, unless we have some braindead
> @@ -65,7 +47,7 @@ u32 __hyp_text __init_stage2_translation(void)
>   	 * return that value for the rest of the kernel to decide what
>   	 * to do.
>   	 */
> -	val |= 64 - (parange > 40 ? 40 : parange);
> +	val |= 64 - (phys_shift > 40 ? 40 : phys_shift);
>   
>   	/*
>   	 * Check the availability of Hardware Access Flag / Dirty Bit
> @@ -86,5 +68,5 @@ u32 __hyp_text __init_stage2_translation(void)
>   
>   	write_sysreg(val, vtcr_el2);
>   
> -	return parange;
> +	return phys_shift;
>   }
> 

-- 
Julien Grall