arm64: Provide a command line to disable spectre_v2 mitigation

There are various reasons, such as benchmarking, to disable spectrev2
mitigation on a machine. Provide a command-line option to do so.

Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Tested-by: Stefan Wahren <stefan.wahren@i2se.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Signed-off-by: Will Deacon <will.deacon@arm.com>

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index cf82bac..6a92925 100644 (file)
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2905,10 +2905,10 @@
                        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 9950bb0..d2b2c69 100644 (file)
--- 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 +239,11 @@ enable_smccc_arch_workaround_1(const struct arm64_cpu_capabilities *entry)
        if (!entry->matches(entry, SCOPE_LOCAL_CPU))
                return;
 
+       if (__nospectre_v2) {
+               pr_info_once("spectrev2 mitigation disabled by command line option\n");
+               return;
+       }
+
        if (psci_ops.smccc_version == SMCCC_VERSION_1_0)
                return;