Commit 877ace9e authored by Liu Song's avatar Liu Song Committed by Catalin Marinas
Browse files

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



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: default avatarLiu Song <liusong@linux.alibaba.com>
Acked-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/1661514050-22263-1-git-send-email-liusong@linux.alibaba.com


Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent 8eb858c4

Documentation/admin-guide/kernel-parameters.txt

+5 −0
Original line number Diff line number Diff line
@@ -3207,6 +3207,7 @@ 
					       spectre_v2_user=off [X86]

					       spec_store_bypass_disable=off [X86,PPC]

					       ssbd=force-off [ARM64]

					       nospectre_bhb [ARM64]

					       l1tf=off [X86]

					       mds=off [X86]

					       tsx_async_abort=off [X86]
@@ -3631,6 +3632,10 @@ 
			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

arch/arm64/kernel/proton-pack.c

+9 −1
Original line number Diff line number Diff line
@@ -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;