[MODERATED] Re: [PATCH v5 07/11] [PATCH v5 07/10] Linux Patch #7

[Borislav Petkov <bp@suse.de>]

On Wed, Apr 25, 2018 at 10:04:22PM -0400, speck for konrad.wilk_at_oracle.com wrote:
> diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
> index dff706bba3aa..99cdd44c20bc 100644
> --- a/arch/x86/kernel/cpu/bugs.c
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -37,8 +37,6 @@ u64 __read_mostly x86_spec_ctrl_base;
>  
>  void __init check_bugs(void)
>  {
> -	identify_boot_cpu();
> -
>  	/*
>  	 * Read the SPEC_CTRL MSR to account for reserved bits which may have
>  	 * unknown values.

This hunk breaks on AMD because after it I see in dmesg:

[    0.038706] Spectre V2 : Spectre mitigation: LFENCE not serializing, switching to generic retpoline

instead of

[    0.049074] Spectre V2 : Mitigation: Full AMD retpoline

because the making LFENCE serializable bit is done in init_amd().

IOW, you need to have the following calling order:

	ssb_select_mitigation
	identify_boot_cpu
	spectre_v2_select_mitigation

Hunk ontop:

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 289eefd6c67e..7f105f3d195a 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -50,9 +50,6 @@ void __init check_bugs(void)
 	if (boot_cpu_has(X86_FEATURE_IBRS))
 		rdmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
 
-	/* Select the proper spectre mitigation before patching alternatives */
-	spectre_v2_select_mitigation();
-
 	/*
 	 * Select proper mitigation for any exposure to the Speculative Store
 	 * Bypass vulnerability.
@@ -60,11 +57,14 @@ void __init check_bugs(void)
 	ssb_select_mitigation();
 
 	/*
-	 * Need to do this _after_ spec_store_bypass_select_mitigation to
-	 * figure if any mitigation should be latched.
+	 * Need to do this _after_ ssb_select_mitigation() to figure if any
+	 * mitigation should be latched.
 	 */
 	identify_boot_cpu();
 
+	/* Select the proper spectre mitigation before patching alternatives */
+	spectre_v2_select_mitigation();
+
 	if (!IS_ENABLED(CONFIG_SMP)) {
 		pr_info("CPU: ");
 		print_cpu_info(&boot_cpu_data);

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
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