x86/bugs: Don't say no mitigation available if kernel not compiled with retpoline

[PATCH v2] x86/bugs: Don't say no mitigation available if kernel not compiled with retpoline

Posted by Kim Phillips 3 weeks, 4 days ago

When the kernel lacks retpoline support, spectre_v2_select_retpoline()
emits

  "Kernel not compiled with retpoline; no mitigation available!"

before returning SPECTRE_V2_NONE to its callers.  SPECTRE_V2_NONE is not
the final answer, though: spectre_v2_update_mitigation() runs afterwards
and can still upgrade the mitigation.

On an Intel CPU affected by RETBleed, built with
CONFIG_MITIGATION_IBRS_ENTRY=y and CONFIG_MITIGATION_RETPOLINE=n, and
booted with spectre_v2=auto, retbleed_select_mitigation() picks
RETBLEED_MITIGATION_IBRS, and spectre_v2_update_mitigation() then promotes
SPECTRE_V2_NONE to SPECTRE_V2_IBRS.  The boot log claims no mitigation is
available immediately before reporting "Spectre V2 : Mitigation: IBRS",
and sysfs reports the machine as mitigated.  The message is alarming and
simply wrong.

Drop "no mitigation available!" because the final mitigation state is
printed afterwards in spectre_v2_update_mitigation() anyway.

Suggested-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Fixes: 480e803dacf8 ("x86/bugs: Restructure spectre_v2 mitigation")
Cc: stable@kernel.org
Signed-off-by: Kim Phillips <kim.phillips@amd.com>
Assisted-by: ClaudeCode:claude-opus-4-7
---
 arch/x86/kernel/cpu/bugs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 56eac5611c31..5a0533a41d30 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1957,7 +1957,7 @@ early_param("spectre_v2", spectre_v2_parse_cmdline);
 static enum spectre_v2_mitigation __init spectre_v2_select_retpoline(void)
 {
 	if (!IS_ENABLED(CONFIG_MITIGATION_RETPOLINE)) {
-		pr_err("Kernel not compiled with retpoline; no mitigation available!");
+		pr_err("Kernel not compiled with retpoline");
 		return SPECTRE_V2_NONE;
 	}
 
-- 
2.43.0

Re: [PATCH v2] x86/bugs: Don't say no mitigation available if kernel not compiled with retpoline

Posted by Pawan Gupta 3 weeks, 3 days ago

On Mon, Aug 31, 2026 at 04:09:16PM -0500, Kim Phillips wrote:
> When the kernel lacks retpoline support, spectre_v2_select_retpoline()
> emits
> 
>   "Kernel not compiled with retpoline; no mitigation available!"
> 
> before returning SPECTRE_V2_NONE to its callers.  SPECTRE_V2_NONE is not
> the final answer, though: spectre_v2_update_mitigation() runs afterwards
> and can still upgrade the mitigation.
> 
> On an Intel CPU affected by RETBleed, built with
> CONFIG_MITIGATION_IBRS_ENTRY=y and CONFIG_MITIGATION_RETPOLINE=n, and
> booted with spectre_v2=auto, retbleed_select_mitigation() picks
> RETBLEED_MITIGATION_IBRS, and spectre_v2_update_mitigation() then promotes
> SPECTRE_V2_NONE to SPECTRE_V2_IBRS.  The boot log claims no mitigation is
> available immediately before reporting "Spectre V2 : Mitigation: IBRS",
> and sysfs reports the machine as mitigated.  The message is alarming and
> simply wrong.
> 
> Drop "no mitigation available!" because the final mitigation state is
> printed afterwards in spectre_v2_update_mitigation() anyway.
> 
> Suggested-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
> Fixes: 480e803dacf8 ("x86/bugs: Restructure spectre_v2 mitigation")
> Cc: stable@kernel.org
> Signed-off-by: Kim Phillips <kim.phillips@amd.com>

Reviewed-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>