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arm64: spectre: increase parameters that can be used to turn off bhb mitigation individually

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[ Upstream commit 877ace9eab7de032f954533afd5d1ecd0cf62eaf ]

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>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/1661514050-22263-1-git-send-email-liusong@linux.alibaba.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Pu Lehui <pulehui@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Liu Song
2025-06-07 15:25:18 +00:00
committed by Greg Kroah-Hartman
parent 86ca67653d
commit d38941ee87
2 changed files with 13 additions and 1 deletions
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5
Documentation/admin-guide/kernel-parameters.txt
View File

@@ -2954,6 +2954,7 @@
spec_store_bypass_disable=off [X86,PPC]
spectre_v2_user=off [X86]
ssbd=force-off [ARM64]
nospectre_bhb [ARM64]
tsx_async_abort=off [X86]
Exceptions:
@@ -3367,6 +3368,10 @@
vulnerability. System may allow data leaks with this
option.
nospectre_bhb [ARM64] Disable all mitigations for Spectre-BHB (branch
history injection) vulnerability. System may allow data leaks
with this option.
nospec_store_bypass_disable
[HW] Disable all mitigations for the Speculative Store Bypass vulnerability

9
arch/arm64/kernel/proton-pack.c
View File

@@ -1088,6 +1088,13 @@ static void kvm_setup_bhb_slot(const char *hyp_vecs_start) { }
#endif /* CONFIG_KVM */
static bool spectre_bhb_fw_mitigated;
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)
{
@@ -1100,7 +1107,7 @@ 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;