linux-kernel - Re: [PATCHv4 05/10] arm64/cpufeature: detect pointer authentication

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Date:   Wed, 23 May 2018 09:48:28 +0100
From:   Suzuki K Poulose <Suzuki.Poulose@....com>
To:     Mark Rutland <mark.rutland@....com>,
        linux-arm-kernel@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, kvmarm@...ts.cs.columbia.edu,
        catalin.marinas@....com, christoffer.dall@....com,
        drjones@...hat.com, marc.zyngier@....com,
        ramana.radhakrishnan@....com, will.deacon@....com,
        awallis@...eaurora.org
Subject: Re: [PATCHv4 05/10] arm64/cpufeature: detect pointer authentication


Mark,

On 03/05/18 14:20, Mark Rutland wrote:
> So that we can dynamically handle the presence of pointer authentication
> functionality, wire up probing code in cpufeature.c.
> 
>  From ARMv8.3 onwards, ID_AA64ISAR1 is no longer entirely RES0, and now
> has four fields describing the presence of pointer authentication
> functionality:
> 
> * APA - address authentication present, using an architected algorithm
> * API - address authentication present, using an IMP DEF algorithm
> * GPA - generic authentication present, using an architected algorithm
> * GPI - generic authentication present, using an IMP DEF algorithm
> 
> For the moment we only care about address authentication, so we only
> need to check APA and API. It is assumed that if all CPUs support an IMP
> DEF algorithm, the same algorithm is used across all CPUs.
> 
> Note that when we implement KVM support, we will also need to ensure
> that CPUs have uniform support for GPA and GPI.
> 
> Signed-off-by: Mark Rutland <mark.rutland@....com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Suzuki K Poulose <suzuki.poulose@....com>
> Cc: Will Deacon <will.deacon@....com>
> ---
>   arch/arm64/include/asm/cpucaps.h |  5 ++++-
>   arch/arm64/kernel/cpufeature.c   | 47 ++++++++++++++++++++++++++++++++++++++++
>   2 files changed, 51 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h
> index bc51b72fafd4..9dcb4d1b14f5 100644
> --- a/arch/arm64/include/asm/cpucaps.h
> +++ b/arch/arm64/include/asm/cpucaps.h
> @@ -48,7 +48,10 @@
>   #define ARM64_HAS_CACHE_IDC			27
>   #define ARM64_HAS_CACHE_DIC			28
>   #define ARM64_HW_DBM				29
> +#define ARM64_HAS_ADDRESS_AUTH_ARCH		30
> +#define ARM64_HAS_ADDRESS_AUTH_IMP_DEF		31

Where are these caps used ? I couldn't find anything in the series
that uses them. Otherwise looks good to me.

Cheers

Suzuki