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SubjectRe: [PATCH v4 02/12] arm64: Provide a command line to disable spectre_v2 mitigation
On Fri, 25 Jan 2019 12:07:01 -0600
Jeremy Linton <jeremy.linton@arm.com> wrote:

Hi,

> There are various reasons, including bencmarking, to disable spectrev2
> mitigation on a machine. Provide a command-line to do so.
>
> Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
> Cc: Jonathan Corbet <corbet@lwn.net>
> Cc: linux-doc@vger.kernel.org

Reviewed-by: Andre Przywara <andre.przywara@arm.com>

Cheers,
Andre

> ---
> Documentation/admin-guide/kernel-parameters.txt | 8 ++++----
> arch/arm64/kernel/cpu_errata.c | 11 +++++++++++
> 2 files changed, 15 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt
> b/Documentation/admin-guide/kernel-parameters.txt index
> 9475f02c79da..2ae77979488e 100644 ---
> a/Documentation/admin-guide/kernel-parameters.txt +++
> b/Documentation/admin-guide/kernel-parameters.txt @@ -2849,10
> +2849,10 @@ check bypass). With this option data leaks are possible
> in the system.
>
> - nospectre_v2 [X86,PPC_FSL_BOOK3E] Disable all
> mitigations for the Spectre variant 2
> - (indirect branch prediction) vulnerability.
> System may
> - allow data leaks with this option, which is
> equivalent
> - to spectre_v2=off.
> + nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all
> mitigations for
> + the Spectre variant 2 (indirect branch
> prediction)
> + vulnerability. System may allow data leaks
> with this
> + option.
>
> nospec_store_bypass_disable
> [HW] Disable all mitigations for the
> Speculative Store Bypass vulnerability diff --git
> a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
> index 9950bb0cbd52..9a7b5fca51a0 100644 ---
> a/arch/arm64/kernel/cpu_errata.c +++ b/arch/arm64/kernel/cpu_errata.c
> @@ -220,6 +220,14 @@ static void qcom_link_stack_sanitization(void)
> : "=&r" (tmp));
> }
>
> +static bool __nospectre_v2;
> +static int __init parse_nospectre_v2(char *str)
> +{
> + __nospectre_v2 = true;
> + return 0;
> +}
> +early_param("nospectre_v2", parse_nospectre_v2);
> +
> static void
> enable_smccc_arch_workaround_1(const struct arm64_cpu_capabilities
> *entry) {
> @@ -231,6 +239,9 @@ enable_smccc_arch_workaround_1(const struct
> arm64_cpu_capabilities *entry) if (!entry->matches(entry,
> SCOPE_LOCAL_CPU)) return;
>
> + if (__nospectre_v2)
> + return;
> +
> if (psci_ops.smccc_version == SMCCC_VERSION_1_0)
> return;
>

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