Re: [PATCH v3 3/7] x86/bugs: Exit early if return thunk is already set

[Borislav Petkov]

On Thu, May 22, 2025 at 06:21:02PM -0700, Pawan Gupta wrote:
> When the exact same return thunk is already set, avoid the warning and exit
> early. This is to prepare for ITS to also set CDT return thunk independent
> of retbleed.
> 
> Signed-off-by: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>
> ---
>  arch/x86/kernel/cpu/bugs.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
> index 94d0de3e61aec32b3b67c8d21f89a8c67b93dff3..354593065025fd7c5727e955d76523777b3da9ee 100644
> --- a/arch/x86/kernel/cpu/bugs.c
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -113,6 +113,9 @@ void (*x86_return_thunk)(void) __ro_after_init = __x86_return_thunk;
>  
>  static void __init set_return_thunk(void *thunk)
>  {
> +	if (thunk == x86_return_thunk)
> +		return;
> +
>  	if (x86_return_thunk != __x86_return_thunk)
>  		pr_warn("x86/bugs: return thunk changed\n");

Ok, let's drop those silly conditionals here and simply issue the name. We'll
see later whether this needs to be louder...

---
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 94d0de3e61ae..20696abd1bef 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -113,10 +113,9 @@ void (*x86_return_thunk)(void) __ro_after_init = __x86_return_thunk;
 
 static void __init set_return_thunk(void *thunk)
 {
-	if (x86_return_thunk != __x86_return_thunk)
-		pr_warn("x86/bugs: return thunk changed\n");
-
 	x86_return_thunk = thunk;
+
+	pr_info("active return thunk: %ps\n", thunk);
 }
 
 /* Update SPEC_CTRL MSR and its cached copy unconditionally */

-- 
Regards/Gruss,
    Boris.

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