linux-kernel - Re: [PATCH v3 3/7] arm64: kpti: move check for non-vulnerable CPUs to a function

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Message-ID: <553c4f17-b504-a7a2-51cf-9c0d6c5d7797@arm.com>
Date:   Mon, 14 Jan 2019 11:32:03 +0000
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     jeremy.linton@....com, linux-arm-kernel@...ts.infradead.org
Cc:     catalin.marinas@....com, will.deacon@....com, marc.zyngier@....com,
        dave.martin@....com, shankerd@...eaurora.org,
        linux-kernel@...r.kernel.org, ykaukab@...e.de,
        julien.thierry@....com, mlangsdo@...hat.com, Steven.Price@....com,
        stefan.wahren@...e.com
Subject: Re: [PATCH v3 3/7] arm64: kpti: move check for non-vulnerable CPUs to
 a function

Hi Jeremy,

On 09/01/2019 23:55, Jeremy Linton wrote:
> From: Mian Yousaf Kaukab <ykaukab@...e.de>
> 
> Add is_meltdown_safe() which is a whitelist of known safe cores.
> 
> Signed-off-by: Mian Yousaf Kaukab <ykaukab@...e.de>
> [Moved location of function]
> Signed-off-by: Jeremy Linton <jeremy.linton@....com>
> ---
>   arch/arm64/kernel/cpufeature.c | 15 +++++++++++----
>   1 file changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 4f272399de89..ab784d7a0083 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -947,8 +947,7 @@ has_useable_cnp(const struct arm64_cpu_capabilities *entry, int scope)
>   #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
>   static int __kpti_forced; /* 0: not forced, >0: forced on, <0: forced off */
>   
> -static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
> -				int scope)
> +static bool is_cpu_meltdown_safe(void)
>   {
>   	/* List of CPUs that are not vulnerable and don't need KPTI */
>   	static const struct midr_range kpti_safe_list[] = {
> @@ -962,6 +961,15 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
>   		MIDR_ALL_VERSIONS(MIDR_CORTEX_A73),
>   		{ /* sentinel */ }
>   	};
> +	if (is_midr_in_range_list(read_cpuid_id(), kpti_safe_list))

nit: Does it make sense to rename the list to "meltdown_safe_list", to match the
function name ?

Also also, you may do :

	return is_midr_in_range_list(read_cpuid_id(), kpti_safe_list);

Either way

Reviewed-by: Suzuki K Poulose <suzuki.poulose@....com>