linux-kernel - Re: [PATCH v2 1/2] arm64: Relax constraints on ID feature bits

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Date:   Wed, 7 Feb 2018 15:10:47 +0000
From:   Suzuki K Poulose <Suzuki.Poulose@....com>
To:     Dave Martin <Dave.Martin@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, mark.rutland@....com,
        marc.zyngier@....com, catalin.marinas@....com, will.deacon@....com,
        linux-kernel@...r.kernel.org, james.morse@....com
Subject: Re: [PATCH v2 1/2] arm64: Relax constraints on ID feature bits

On 07/02/18 15:09, Dave Martin wrote:
> On Wed, Feb 07, 2018 at 02:21:05PM +0000, Suzuki K Poulose wrote:

...

> [...]
> 
>> -	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64MMFR0_ASID_SHIFT, 4, 0),
>> +	/*
>> +	 * We handle differing ASID widths by explicit checks to make sure the system is
>> +	 * safe via verify_cpu_asid_bits()
> 
> I guess that's sufficient.
> 
> Although I had suggested adding a comment to verify_cpu_asid_bits()
> cross-referencing back to here, it now seems superfluous.  It's fairly
> obvious what that function is supported to do.
> 
> 
> [...]
> 
>> -	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64MMFR1_VHE_SHIFT, 4, 0),
> 
> [...]
> 
>> +	/*
>> +	 * When CONFIG_ARM64_VHE is enabled, we ensure that there is no conflict in run
>> +	 * levels via verify_cpu_run_el()
>> +	 */
>> +	ARM64_FTR_BITS(FTR_HIDDEN, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64MMFR1_VHE_SHIFT, 4, 0),
> 
> Similarly ack.
> 
> 
> [...]
> 
>> -	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64MMFR2_IESB_SHIFT, 4, 0),
> 
> [...]
> 
>> +	/*
>> +	 * Lacking implicit ESB on exception boundaries on a subset of CPUs is no worse than
>> +	 * lacking it on all of them.
>> +	 */
>> +	ARM64_FTR_BITS(FTR_HIDDEN, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64MMFR2_IESB_SHIFT, 4, 0),
> 
> And again.  Thanks.
> 
> [...]
> 
> Reviewed-by: Dave Martin <Dave.Martin@....com>
> 


Thanks Dave !