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   1 From stable+bounces-151861-greg=kroah.com@vger.kernel.org Sat Jun  7 17:41:40 2025
   2 From: Pu Lehui <pulehui@huaweicloud.com>
   3 Date: Sat,  7 Jun 2025 15:25:18 +0000
   4 Subject: arm64: spectre: increase parameters that can be used to turn off bhb mitigation individually
   5 To: stable@vger.kernel.org
   6 Cc: james.morse@arm.com, catalin.marinas@arm.com, daniel@iogearbox.net, ast@kernel.org, andrii@kernel.org, xukuohai@huawei.com, pulehui@huawei.com
   7 Message-ID: <20250607152521.2828291-12-pulehui@huaweicloud.com>
   8
   9 From: Liu Song <liusong@linux.alibaba.com>
  10
  11 [ Upstream commit 877ace9eab7de032f954533afd5d1ecd0cf62eaf ]
  12
  13 In our environment, it was found that the mitigation BHB has a great
  14 impact on the benchmark performance. For example, in the lmbench test,
  15 the "process fork && exit" test performance drops by 20%.
  16 So it is necessary to have the ability to turn off the mitigation
  17 individually through cmdline, thus avoiding having to compile the
  18 kernel by adjusting the config.
  19
  20 Signed-off-by: Liu Song <liusong@linux.alibaba.com>
  21 Acked-by: Catalin Marinas <catalin.marinas@arm.com>
  22 Link: https://lore.kernel.org/r/1661514050-22263-1-git-send-email-liusong@linux.alibaba.com
  23 Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
  24 Signed-off-by: Pu Lehui <pulehui@huawei.com>
  25 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  26 ---
  27  Documentation/admin-guide/kernel-parameters.txt |    5 +++++
  28  arch/arm64/kernel/proton-pack.c                 |    9 ++++++++-
  29  2 files changed, 13 insertions(+), 1 deletion(-)
  30
  31 --- a/Documentation/admin-guide/kernel-parameters.txt
  32 +++ b/Documentation/admin-guide/kernel-parameters.txt
  33 @@ -2954,6 +2954,7 @@
  34                                                spec_store_bypass_disable=off [X86,PPC]
  35                                                spectre_v2_user=off [X86]
  36                                                ssbd=force-off [ARM64]
  37 +                                              nospectre_bhb [ARM64]
  38                                                tsx_async_abort=off [X86]
  39
  40                                 Exceptions:
  41 @@ -3367,6 +3368,10 @@
  42                         vulnerability. System may allow data leaks with this
  43                         option.
  44
  45 +       nospectre_bhb   [ARM64] Disable all mitigations for Spectre-BHB (branch
  46 +                       history injection) vulnerability. System may allow data leaks
  47 +                       with this option.
  48 +
  49         nospec_store_bypass_disable
  50                         [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
  51
  52 --- a/arch/arm64/kernel/proton-pack.c
  53 +++ b/arch/arm64/kernel/proton-pack.c
  54 @@ -1088,6 +1088,13 @@ static void kvm_setup_bhb_slot(const cha
  55  #endif /* CONFIG_KVM */
  56
  57  static bool spectre_bhb_fw_mitigated;
  58 +static bool __read_mostly __nospectre_bhb;
  59 +static int __init parse_spectre_bhb_param(char *str)
  60 +{
  61 +       __nospectre_bhb = true;
  62 +       return 0;
  63 +}
  64 +early_param("nospectre_bhb", parse_spectre_bhb_param);
  65
  66  void spectre_bhb_enable_mitigation(const struct arm64_cpu_capabilities *entry)
  67  {
  68 @@ -1100,7 +1107,7 @@ void spectre_bhb_enable_mitigation(const
  69                 /* No point mitigating Spectre-BHB alone. */
  70         } else if (!IS_ENABLED(CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY)) {
  71                 pr_info_once("spectre-bhb mitigation disabled by compile time option\n");
  72 -       } else if (cpu_mitigations_off()) {
  73 +       } else if (cpu_mitigations_off() || __nospectre_bhb) {
  74                 pr_info_once("spectre-bhb mitigation disabled by command line option\n");
  75         } else if (supports_ecbhb(SCOPE_LOCAL_CPU)) {
  76                 state = SPECTRE_MITIGATED;