On Tue, Jun 09, 2020 at 08:53:49AM -0000, tip-bot2 for Anthony Steinhauser
wrote:
> @@ -672,23 +665,36 @@ spectre_v2_user_select_mitigation(enum
> spectre_v2_mitigation_cmd v2_cmd)
> pr_info("mitigation: Enabling %s Indirect Branch Prediction
> Barrier\n",
> static_key_enabled(&switch_mm_always_ibpb) ?
> "always-on" : "conditional");
> +
> + spectre_v2_user_ibpb = mode;
> }
>
> - /* If enhanced IBRS is enabled no STIBP required */
> - if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
> + /*
> + * If enhanced IBRS is enabled or SMT impossible, STIBP is not
> + * required.
> + */
> + if (!smt_possible || spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
> return;
>
> /*
> - * If SMT is not possible or STIBP is not available clear the STIBP
> - * mode.
> + * At this point, an STIBP mode other than "off" has been set.
> + * If STIBP support is not being forced, check if STIBP always-on
> + * is preferred.
> + */
> + if (mode != SPECTRE_V2_USER_STRICT &&
> + boot_cpu_has(X86_FEATURE_AMD_STIBP_ALWAYS_ON))
> + mode = SPECTRE_V2_USER_STRICT_PREFERRED;
> +
> + /*
> + * If STIBP is not available, clear the STIBP mode.
> */
> - if (!smt_possible || !boot_cpu_has(X86_FEATURE_STIBP))
> + if (!boot_cpu_has(X86_FEATURE_STIBP))
> mode = SPECTRE_V2_USER_NONE;
Can we merge this test into the one above? Diff ontop:
---
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 8d57562b1d2c..05b3163e1b8c 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -673,7 +673,9 @@ spectre_v2_user_select_mitigation(enum
spectre_v2_mitigation_cmd v2_cmd)
* If enhanced IBRS is enabled or SMT impossible, STIBP is not
* required.
*/
- if (!smt_possible || spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
+ if (!boot_cpu_has(X86_FEATURE_STIBP) ||
+ !smt_possible ||
+ spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
return;
/*
@@ -685,12 +687,6 @@ spectre_v2_user_select_mitigation(enum
spectre_v2_mitigation_cmd v2_cmd)
boot_cpu_has(X86_FEATURE_AMD_STIBP_ALWAYS_ON))
mode = SPECTRE_V2_USER_STRICT_PREFERRED;
- /*
- * If STIBP is not available, clear the STIBP mode.
- */
- if (!boot_cpu_has(X86_FEATURE_STIBP))
- mode = SPECTRE_V2_USER_NONE;
-
spectre_v2_user_stibp = mode;
set_mode:
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
