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Message-ID: <20250814165459.uhrxpcybihzddbgt@desk>
Date: Thu, 14 Aug 2025 09:54:59 -0700
From: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To: David Kaplan <david.kaplan@....com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>,
Peter Zijlstra <peterz@...radead.org>,
Josh Poimboeuf <jpoimboe@...nel.org>,
Ingo Molnar <mingo@...hat.com>,
Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
"H . Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] x86/bugs: Use early_param for spectre_v2
On Mon, Aug 11, 2025 at 09:26:58AM -0500, David Kaplan wrote:
> Most of the mitigations in bugs.c use early_param for command line parsing.
> Rework the spectre_v2 and nospectre_v2 command line options to be
> consistent with the others.
>
> Signed-off-by: David Kaplan <david.kaplan@....com>
> ---
> arch/x86/kernel/cpu/bugs.c | 151 +++++++++++++++++++------------------
> 1 file changed, 78 insertions(+), 73 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
> index 6bfe199b9f3e..19a3891953c3 100644
> --- a/arch/x86/kernel/cpu/bugs.c
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -1827,7 +1827,8 @@ enum spectre_v2_mitigation_cmd {
> SPECTRE_V2_CMD_IBRS,
> };
>
> -static enum spectre_v2_mitigation_cmd spectre_v2_cmd __ro_after_init = SPECTRE_V2_CMD_AUTO;
> +static enum spectre_v2_mitigation_cmd spectre_v2_cmd __ro_after_init =
> + IS_ENABLED(CONFIG_MITIGATION_SPECTRE_V2) ? SPECTRE_V2_CMD_AUTO : SPECTRE_V2_CMD_NONE;
>
> enum spectre_v2_user_mitigation_cmd {
> SPECTRE_V2_USER_CMD_NONE,
> @@ -2035,112 +2036,118 @@ static const char * const spectre_v2_strings[] = {
> [SPECTRE_V2_IBRS] = "Mitigation: IBRS",
> };
>
> -static const struct {
> - const char *option;
> - enum spectre_v2_mitigation_cmd cmd;
> - bool secure;
> -} mitigation_options[] __initconst = {
> - { "off", SPECTRE_V2_CMD_NONE, false },
> - { "on", SPECTRE_V2_CMD_FORCE, true },
> - { "retpoline", SPECTRE_V2_CMD_RETPOLINE, false },
> - { "retpoline,amd", SPECTRE_V2_CMD_RETPOLINE_LFENCE, false },
> - { "retpoline,lfence", SPECTRE_V2_CMD_RETPOLINE_LFENCE, false },
> - { "retpoline,generic", SPECTRE_V2_CMD_RETPOLINE_GENERIC, false },
> - { "eibrs", SPECTRE_V2_CMD_EIBRS, false },
> - { "eibrs,lfence", SPECTRE_V2_CMD_EIBRS_LFENCE, false },
> - { "eibrs,retpoline", SPECTRE_V2_CMD_EIBRS_RETPOLINE, false },
> - { "auto", SPECTRE_V2_CMD_AUTO, false },
> - { "ibrs", SPECTRE_V2_CMD_IBRS, false },
> -};
> -
> static void __init spec_v2_print_cond(const char *reason, bool secure)
> {
> if (boot_cpu_has_bug(X86_BUG_SPECTRE_V2) != secure)
> pr_info("%s selected on command line.\n", reason);
> }
>
> -static enum spectre_v2_mitigation_cmd __init spectre_v2_parse_cmdline(void)
> -{
> - enum spectre_v2_mitigation_cmd cmd;
> - char arg[20];
> - int ret, i;
> +static bool nospectre_v2 __ro_after_init;
>
> - cmd = IS_ENABLED(CONFIG_MITIGATION_SPECTRE_V2) ? SPECTRE_V2_CMD_AUTO : SPECTRE_V2_CMD_NONE;
> - if (cmdline_find_option_bool(boot_command_line, "nospectre_v2"))
> - return SPECTRE_V2_CMD_NONE;
> +static int __init nospectre_v2_parse_cmdline(char *str)
> +{
> + nospectre_v2 = true;
> + spectre_v2_cmd = SPECTRE_V2_CMD_NONE;
> + return 0;
> +}
> +early_param("nospectre_v2", nospectre_v2_parse_cmdline);
>
> - ret = cmdline_find_option(boot_command_line, "spectre_v2", arg, sizeof(arg));
> - if (ret < 0)
> - return cmd;
> +static int __init spectre_v2_parse_cmdline(char *str)
> +{
> + if (!str)
> + return -EINVAL;
>
> - for (i = 0; i < ARRAY_SIZE(mitigation_options); i++) {
> - if (!match_option(arg, ret, mitigation_options[i].option))
> - continue;
> - cmd = mitigation_options[i].cmd;
> - break;
> - }
> + if (nospectre_v2)
> + return 0;
>
> - if (i >= ARRAY_SIZE(mitigation_options)) {
> - pr_err("unknown option (%s). Switching to default mode\n", arg);
> - return cmd;
> - }
> + if (!strcmp(str, "off"))
> + spectre_v2_cmd = SPECTRE_V2_CMD_NONE;
> + else if (!strcmp(str, "on"))
> + spectre_v2_cmd = SPECTRE_V2_CMD_FORCE;
> + else if (!strcmp(str, "retpoline"))
> + spectre_v2_cmd = SPECTRE_V2_CMD_RETPOLINE;
> + else if (!strcmp(str, "retpoline,amd") ||
> + !strcmp(str, "retpoline,lfence"))
> + spectre_v2_cmd = SPECTRE_V2_CMD_RETPOLINE_LFENCE;
> + else if (!strcmp(str, "retpoline,generic"))
> + spectre_v2_cmd = SPECTRE_V2_CMD_RETPOLINE_GENERIC;
> + else if (!strcmp(str, "eibrs"))
> + spectre_v2_cmd = SPECTRE_V2_CMD_EIBRS;
> + else if (!strcmp(str, "eibrs,lfence"))
> + spectre_v2_cmd = SPECTRE_V2_CMD_EIBRS_LFENCE;
> + else if (!strcmp(str, "eibrs,retpoline"))
> + spectre_v2_cmd = SPECTRE_V2_CMD_EIBRS_RETPOLINE;
> + else if (!strcmp(str, "auto"))
> + spectre_v2_cmd = SPECTRE_V2_CMD_AUTO;
> + else if (!strcmp(str, "ibrs"))
> + spectre_v2_cmd = SPECTRE_V2_CMD_IBRS;
> + else
> + pr_err("Ignoring unknown spectre_v2 option (%s).", str);
All of the below should go in spectre_v2_select_mitigation() after all
features are detected because ...
> - if ((cmd == SPECTRE_V2_CMD_RETPOLINE ||
> - cmd == SPECTRE_V2_CMD_RETPOLINE_LFENCE ||
> - cmd == SPECTRE_V2_CMD_RETPOLINE_GENERIC ||
> - cmd == SPECTRE_V2_CMD_EIBRS_LFENCE ||
> - cmd == SPECTRE_V2_CMD_EIBRS_RETPOLINE) &&
> + if ((spectre_v2_cmd == SPECTRE_V2_CMD_RETPOLINE ||
> + spectre_v2_cmd == SPECTRE_V2_CMD_RETPOLINE_LFENCE ||
> + spectre_v2_cmd == SPECTRE_V2_CMD_RETPOLINE_GENERIC ||
> + spectre_v2_cmd == SPECTRE_V2_CMD_EIBRS_LFENCE ||
> + spectre_v2_cmd == SPECTRE_V2_CMD_EIBRS_RETPOLINE) &&
> !IS_ENABLED(CONFIG_MITIGATION_RETPOLINE)) {
> pr_err("%s selected but not compiled in. Switching to AUTO select\n",
> - mitigation_options[i].option);
> - return SPECTRE_V2_CMD_AUTO;
> + str);
> + spectre_v2_cmd = SPECTRE_V2_CMD_AUTO;
> }
>
> - if ((cmd == SPECTRE_V2_CMD_EIBRS ||
> - cmd == SPECTRE_V2_CMD_EIBRS_LFENCE ||
> - cmd == SPECTRE_V2_CMD_EIBRS_RETPOLINE) &&
> + if ((spectre_v2_cmd == SPECTRE_V2_CMD_EIBRS ||
> + spectre_v2_cmd == SPECTRE_V2_CMD_EIBRS_LFENCE ||
> + spectre_v2_cmd == SPECTRE_V2_CMD_EIBRS_RETPOLINE) &&
> !boot_cpu_has(X86_FEATURE_IBRS_ENHANCED)) {
... X86_FEATURE_IBRS_ENHANCED is not enumerated yet in early_param processing.
> pr_err("%s selected but CPU doesn't have Enhanced or Automatic IBRS. Switching to AUTO select\n",
> - mitigation_options[i].option);
> - return SPECTRE_V2_CMD_AUTO;
> + str);
> + spectre_v2_cmd = SPECTRE_V2_CMD_AUTO;
> }
>
> - if ((cmd == SPECTRE_V2_CMD_RETPOLINE_LFENCE ||
> - cmd == SPECTRE_V2_CMD_EIBRS_LFENCE) &&
> + if ((spectre_v2_cmd == SPECTRE_V2_CMD_RETPOLINE_LFENCE ||
> + spectre_v2_cmd == SPECTRE_V2_CMD_EIBRS_LFENCE) &&
> !boot_cpu_has(X86_FEATURE_LFENCE_RDTSC)) {
and this. So in essence, spectre_v2_parse_cmdline() should only record what
user wanted.
> pr_err("%s selected, but CPU doesn't have a serializing LFENCE. Switching to AUTO select\n",
> - mitigation_options[i].option);
> - return SPECTRE_V2_CMD_AUTO;
> + str);
> + spectre_v2_cmd = SPECTRE_V2_CMD_AUTO;
> }
>
> - if (cmd == SPECTRE_V2_CMD_IBRS && !IS_ENABLED(CONFIG_MITIGATION_IBRS_ENTRY)) {
> + if (spectre_v2_cmd == SPECTRE_V2_CMD_IBRS && !IS_ENABLED(CONFIG_MITIGATION_IBRS_ENTRY)) {
> pr_err("%s selected but not compiled in. Switching to AUTO select\n",
> - mitigation_options[i].option);
> - return SPECTRE_V2_CMD_AUTO;
> + str);
> + spectre_v2_cmd = SPECTRE_V2_CMD_AUTO;
> }
>
> - if (cmd == SPECTRE_V2_CMD_IBRS && boot_cpu_data.x86_vendor != X86_VENDOR_INTEL) {
> + if (spectre_v2_cmd == SPECTRE_V2_CMD_IBRS && boot_cpu_data.x86_vendor != X86_VENDOR_INTEL) {
> pr_err("%s selected but not Intel CPU. Switching to AUTO select\n",
> - mitigation_options[i].option);
> - return SPECTRE_V2_CMD_AUTO;
> + str);
> + spectre_v2_cmd = SPECTRE_V2_CMD_AUTO;
> }
>
> - if (cmd == SPECTRE_V2_CMD_IBRS && !boot_cpu_has(X86_FEATURE_IBRS)) {
> + if (spectre_v2_cmd == SPECTRE_V2_CMD_IBRS && !boot_cpu_has(X86_FEATURE_IBRS)) {
> pr_err("%s selected but CPU doesn't have IBRS. Switching to AUTO select\n",
> - mitigation_options[i].option);
> - return SPECTRE_V2_CMD_AUTO;
> + str);
> + spectre_v2_cmd = SPECTRE_V2_CMD_AUTO;
> }
>
> - if (cmd == SPECTRE_V2_CMD_IBRS && cpu_feature_enabled(X86_FEATURE_XENPV)) {
> + if (spectre_v2_cmd == SPECTRE_V2_CMD_IBRS && cpu_feature_enabled(X86_FEATURE_XENPV)) {
> pr_err("%s selected but running as XenPV guest. Switching to AUTO select\n",
> - mitigation_options[i].option);
> - return SPECTRE_V2_CMD_AUTO;
> + str);
> + spectre_v2_cmd = SPECTRE_V2_CMD_AUTO;
> }
>
> - spec_v2_print_cond(mitigation_options[i].option,
> - mitigation_options[i].secure);
> - return cmd;
> + /* Print a warning if forcing an option. AUTO is not forcing. */
> + if (spectre_v2_cmd == SPECTRE_V2_CMD_AUTO)
> + return 0;
> +
> + if (spectre_v2_cmd == SPECTRE_V2_CMD_FORCE)
> + spec_v2_print_cond(str, true);
> + else
> + spec_v2_print_cond(str, false);
> +
> + return 0;
> }
> +early_param("spectre_v2", spectre_v2_parse_cmdline);
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