linux-kernel - Re: [PATCH v6] arm64: Work around Falkor erratum 1003

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Message-ID: <20170208163441.GC32756@e104818-lin.cambridge.arm.com>
Date:   Wed, 8 Feb 2017 16:34:41 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Christopher Covington <cov@...eaurora.org>
Cc:     Jonathan Corbet <corbet@....net>,
        Marc Zyngier <marc.zyngier@....com>,
        Will Deacon <will.deacon@....com>, linux-doc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Mark Rutland <mark.rutland@....com>,
        linux-kernel@...r.kernel.org, shankerd@...eaurora.org,
        timur@...eaurora.org, Jon Masters <jcm@...hat.com>,
        Neil Leeder <nleeder@...eaurora.org>,
        Mark Langsdorf <mlangsdo@...hat.com>,
        Mark Salter <msalter@...hat.com>
Subject: Re: [PATCH v6] arm64: Work around Falkor erratum 1003

On Tue, Feb 07, 2017 at 07:35:16PM -0500, Christopher Covington wrote:
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -480,6 +480,18 @@ config CAVIUM_ERRATUM_27456
>  
>  	  If unsure, say Y.
>  
> +config QCOM_FALKOR_ERRATUM_1003
> +	bool "Falkor E1003: Incorrect translation due to ASID change"
> +	default y
> +	select ARM64_PAN if ARM64_SW_TTBR0_PAN
> +	help
> +	  On Falkor v1, an incorrect ASID may be cached in the TLB when ASID
> +	  and BADDR are changed together in TTBRx_EL1. The workaround for this
> +	  issue is to use a reserved ASID in cpu_do_switch_mm() before
> +	  switching to the new ASID.
> +
> +	  If unsure, say Y.

It would be good to have a comment here on why PAN is selected.

> --- a/arch/arm64/mm/context.c
> +++ b/arch/arm64/mm/context.c
> @@ -79,6 +79,13 @@ void verify_cpu_asid_bits(void)
>  	}
>  }
>  
> +static void set_reserved_asid_bits(void)
> +{
> +	if (IS_ENABLED(CONFIG_QCOM_FALKOR_ERRATUM_1003) &&
> +	    cpus_have_cap(ARM64_WORKAROUND_QCOM_FALKOR_E1003))
> +		__set_bit(FALKOR_RESERVED_ASID, asid_map);
> +}

You should use cpus_have_const_cap() as it would be optimised using jump
labels.

-- 
Catalin