Re: [PATCH 1/3] cpu/bugs: Fix selecting Automatic IBRS using spectre_v2=eibrs

[Dave Hansen]

On 2/24/26 10:01, Kim Phillips wrote:
> @@ -2136,7 +2136,8 @@ static void __init spectre_v2_select_mitigation(void)
>  	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)) {
> +	    !(boot_cpu_has(X86_FEATURE_IBRS_ENHANCED) ||
> +	      boot_cpu_has(X86_FEATURE_AUTOIBRS))) {
>  		pr_err("EIBRS selected but CPU doesn't have Enhanced or Automatic IBRS. Switching to AUTO select\n");
>  		spectre_v2_cmd = SPECTRE_V2_CMD_AUTO;
>  	}

Didn't we agree to just use the "Intel feature" name? See this existing
code:

>         /*
>          * AMD's AutoIBRS is equivalent to Intel's eIBRS - use the Intel feature
>          * flag and protect from vendor-specific bugs via the whitelist.
>          *
>          * Don't use AutoIBRS when SNP is enabled because it degrades host
>          * userspace indirect branch performance.
>          */
>         if ((x86_arch_cap_msr & ARCH_CAP_IBRS_ALL) ||
>             (cpu_has(c, X86_FEATURE_AUTOIBRS) &&
>              !cpu_feature_enabled(X86_FEATURE_SEV_SNP))) {
>                 setup_force_cpu_cap(X86_FEATURE_IBRS_ENHANCED);
>                 if (!cpu_matches(cpu_vuln_whitelist, NO_EIBRS_PBRSB) &&
>                     !(x86_arch_cap_msr & ARCH_CAP_PBRSB_NO))
>                         setup_force_cpu_bug(X86_BUG_EIBRS_PBRSB);
>         }

You're probably not seeing X86_FEATURE_IBRS_ENHANCED because it doesn't
get forced under SNP.