linux-kernel - Re: [PATCH V3 02/16] arm64/cpufeature: Drop TraceFilt feature exposure from ID

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Date:   Mon, 4 May 2020 21:24:54 +0100
From:   Will Deacon <will@...nel.org>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Catalin Marinas <catalin.marinas@....com>,
        Marc Zyngier <maz@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 02/16] arm64/cpufeature: Drop TraceFilt feature
 exposure from ID_DFR0 register

On Sat, May 02, 2020 at 07:03:51PM +0530, Anshuman Khandual wrote:
> ID_DFR0 based TraceFilt feature should not be exposed to guests. Hence lets
> drop it.
> 
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Marc Zyngier <maz@...nel.org>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: James Morse <james.morse@....com>
> Cc: Suzuki K Poulose <suzuki.poulose@....com>
> Cc: linux-arm-kernel@...ts.infradead.org
> Cc: linux-kernel@...r.kernel.org
> 
> Suggested-by: Mark Rutland <mark.rutland@....com>
> Reviewed-by: Suzuki K Poulose <suzuki.poulose@....com>
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> ---
>  arch/arm64/kernel/cpufeature.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 6d032fbe416f..51386dade423 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -435,7 +435,6 @@ static const struct arm64_ftr_bits ftr_id_pfr1[] = {
>  };
>  
>  static const struct arm64_ftr_bits ftr_id_dfr0[] = {
> -	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, 28, 4, 0),

Hmm, this still confuses me. Is this not now FTR_NONSTRICT? Why is that ok?

Will