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SubjectRe: [PATCH 1/6] arm64: kpti: move check for non-vulnerable CPUs to a function
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Hi,

On 06/12/2018 23:44, Jeremy Linton wrote:
> From: Mian Yousaf Kaukab <ykaukab@suse.de>
>
> Add is_meltdown_safe() which is a whitelist of known safe cores.
>
> Signed-off-by: Mian Yousaf Kaukab <ykaukab@suse.de>
> [Moved location of function]
> Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
> ---
> arch/arm64/kernel/cpufeature.c | 16 ++++++++++++----
> 1 file changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index aec5ecb85737..242898395f68 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -908,8 +908,7 @@ 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[] = {
> @@ -917,6 +916,16 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
> MIDR_ALL_VERSIONS(MIDR_BRCM_VULCAN),
> { /* sentinel */ }
> };
> + /* Don't force KPTI for CPUs that are not vulnerable */

This is really a nit, but that comment would make more sense where
is_cpu_meltdown_safe() is called since unmap_kernel_at_el0 is the one
deciding whether to apply KPTI, is_cpu_meltdown_safe() just states
whether the core is safe of not.

Otherwise:

Reviewed-by: Julien Thierry <julien.thierry@arm.com>

Cheers,

Julien

> + if (is_midr_in_range_list(read_cpuid_id(), kpti_safe_list))
> + return true;
> +
> + return false;
> +}
> +
> +static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
> + int scope)
> +{
> char const *str = "command line option";
>
> /*
> @@ -940,8 +949,7 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
> if (IS_ENABLED(CONFIG_RANDOMIZE_BASE))
> return true;
>
> - /* Don't force KPTI for CPUs that are not vulnerable */
> - if (is_midr_in_range_list(read_cpuid_id(), kpti_safe_list))
> + if (is_cpu_meltdown_safe())
> return false;
>
> /* Defer to CPU feature registers */
>

--
Julien Thierry

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