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Subject[PATCH] arm64: spectre: increase parameters that can be used to turn off bhb mitigation individually
Date
From: Liu Song <liusong@linux.alibaba.com>

In our environment, it was found that the mitigation BHB has a great
impact on the benchmark performance. For example, in the lmbench test,
the "process fork && exit" test performance drops by 20%.
So it is necessary to have the ability to turn off the mitigation
individually through cmdline, thus avoiding having to compile the
kernel by adjusting the config.

Signed-off-by: Liu Song <liusong@linux.alibaba.com>
---
arch/arm64/kernel/proton-pack.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/proton-pack.c b/arch/arm64/kernel/proton-pack.c
index 40be3a7..bd16903 100644
--- a/arch/arm64/kernel/proton-pack.c
+++ b/arch/arm64/kernel/proton-pack.c
@@ -988,6 +988,14 @@ static void this_cpu_set_vectors(enum arm64_bp_harden_el1_vectors slot)
isb();
}

+static bool __read_mostly __nospectre_bhb;
+static int __init parse_spectre_bhb_param(char *str)
+{
+ __nospectre_bhb = true;
+ return 0;
+}
+early_param("nospectre_bhb", parse_spectre_bhb_param);
+
void spectre_bhb_enable_mitigation(const struct arm64_cpu_capabilities *entry)
{
bp_hardening_cb_t cpu_cb;
@@ -1001,7 +1009,7 @@ void spectre_bhb_enable_mitigation(const struct arm64_cpu_capabilities *entry)
/* No point mitigating Spectre-BHB alone. */
} else if (!IS_ENABLED(CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY)) {
pr_info_once("spectre-bhb mitigation disabled by compile time option\n");
- } else if (cpu_mitigations_off()) {
+ } else if (cpu_mitigations_off() || __nospectre_bhb) {
pr_info_once("spectre-bhb mitigation disabled by command line option\n");
} else if (supports_ecbhb(SCOPE_LOCAL_CPU)) {
state = SPECTRE_MITIGATED;
--
1.8.3.1
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