linux-kernel - Re: [PATCH AUTOSEL 4.18 074/131] ARM: 8783/1: NOMMU: Extend check for VBAR support

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Message-ID: <bb9d354b-6a8f-529e-3e62-0d250b967b1a@arm.com>
Date:   Mon, 10 Sep 2018 10:41:43 +0100
From:   Vladimir Murzin <vladimir.murzin@....com>
To:     Sasha Levin <Alexander.Levin@...rosoft.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     Russell King <rmk+kernel@...linux.org.uk>
Subject: Re: [PATCH AUTOSEL 4.18 074/131] ARM: 8783/1: NOMMU: Extend check for
 VBAR support

On 02/09/18 14:04, Sasha Levin wrote:
> From: Vladimir Murzin <vladimir.murzin@....com>
> 
> [ Upstream commit c803ce3f18bd93b3b4a15d1da0c5b5ebc60e0b85 ]
> 
> ARMv8R adds support for VBAR and updates ID_PFR1 with the new filed
> Sec_frac (bits [23:20]):
> 
> Security fractional field. When the Security field is 0000, determines
> the support for features from the ARMv7 Security Extensions. Permitted
> values are:
> 
> 0000 No features from the ARMv7 Security Extensions are implemented.
>      This value is not supported in ARMv8 if ID_PFR1 bits [7:4] are zero.
> 
> 0001 The implementation includes the VBAR, and the TCR.PD0 and TCR.PD1
>      bits.
> 
> 0010 As for 0001, plus the ability to access Secure or Non-secure
>      physical memory is supported.
> 
> All other values are reserved.
> 
> This field is only valid when ID_PFR1[7:4] == 0, otherwise it holds
> the value 0000.
> 
> Signed-off-by: Vladimir Murzin <vladimir.murzin@....com>
> Signed-off-by: Russell King <rmk+kernel@...linux.org.uk>
> Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
> ---
>  arch/arm/mm/nommu.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/mm/nommu.c b/arch/arm/mm/nommu.c
> index 5dd6c58d653b..7d67c70bbded 100644
> --- a/arch/arm/mm/nommu.c
> +++ b/arch/arm/mm/nommu.c
> @@ -53,7 +53,8 @@ static inline bool security_extensions_enabled(void)
>  {
>  	/* Check CPUID Identification Scheme before ID_PFR1 read */
>  	if ((read_cpuid_id() & 0x000f0000) == 0x000f0000)
> -		return !!cpuid_feature_extract(CPUID_EXT_PFR1, 4);
> +		return cpuid_feature_extract(CPUID_EXT_PFR1, 4) ||
> +			cpuid_feature_extract(CPUID_EXT_PFR1, 20);
>  	return 0;
>  }
>  
> 

NAK - it is not stable material.

Thanks
Vladimir