x86/speculation: Change STIPB to STIBP

Since conditional STIBP is the default, it should be treated as the likely case. Changes the use of static_branch_unlikely() to static_branch_likely() for switch_to_cond_stibp.

Signed-off-by Waiman Long <[email protected]>

---
 arch/x86/kernel/cpu/bugs.c | 2 +-
 arch/x86/kernel/process.c  | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

arch/x86/kernel/cpu/bugs.c +1 -1

index a68b32c..bd11119 100644
@@ -153,7 +153,7 @@ void __init check_bugs(void)
 			hostval |= ssbd_tif_to_spec_ctrl(ti->flags);
 
 		/* Conditional STIBP enabled? */
-		if (static_branch_unlikely(&switch_to_cond_stibp))
+		if (static_branch_likely(&switch_to_cond_stibp))
 			hostval |= stibp_tif_to_spec_ctrl(ti->flags);
 
 		if (hostval != guestval) {

arch/x86/kernel/process.c +1 -1

index 7d31192..39a21ae 100644
@@ -434,7 +434,7 @@ static __always_inline void __speculation_ctrl_update(unsigned long tifp,
 	 * otherwise avoid the MSR write.
 	 */
 	if (IS_ENABLED(CONFIG_SMP) &&
-	    static_branch_unlikely(&switch_to_cond_stibp)) {
+	    static_branch_likely(&switch_to_cond_stibp)) {
 		updmsr |= !!(tif_diff & _TIF_SPEC_IB);
 		msr |= stibp_tif_to_spec_ctrl(tifn);
 	}

Signature · 1 line

1.8.3.1

Quoted 3 lines · Waiman Long

Since conditional STIBP is the default, it should be treated as the likely case. Changes the use of static_branch_unlikely() to static_branch_likely() for switch_to_cond_stibp.

So now you're making kernels on 'fixed' or unaffected hardware slower.

Quoted 5 lines · Peter Zijlstra

Quoted 3 lines · Waiman Long

Since conditional STIBP is the default, it should be treated as the likely case. Changes the use of static_branch_unlikely() to static_branch_likely() for switch_to_cond_stibp.

So now you're making kernels on 'fixed' or unaffected hardware slower.

Good point.

The reason I sent out this patch is because of the inconsistency in the use of likely/unlikely hints.

arch/x86/kernel/cpu/bugs.c:156:        if
(static_branch_unlikely(&switch_to_cond_stibp))
arch/x86/kernel/process.c:440:
static_branch_unlikely(&switch_to_cond_stibp)) {
arch/x86/kernel/process.h:26:        if
(!static_branch_likely(&switch_to_cond_stibp)) {

So if we are aiming to optimize for "fixed" or unaffected hardware, maybe we should modify the likely hint to unlikely then.

Quoted 19 lines · Waiman Long

Quoted 5 lines · Peter Zijlstra

Quoted 3 lines · Waiman Long

Since conditional STIBP is the default, it should be treated as the likely case. Changes the use of static_branch_unlikely() to static_branch_likely() for switch_to_cond_stibp.

So now you're making kernels on 'fixed' or unaffected hardware slower.

Good point.

The reason I sent out this patch is because of the inconsistency in the use of likely/unlikely hints.

arch/x86/kernel/cpu/bugs.c:156:        if
(static_branch_unlikely(&switch_to_cond_stibp))
arch/x86/kernel/process.c:440:
static_branch_unlikely(&switch_to_cond_stibp)) {
arch/x86/kernel/process.h:26:        if
(!static_branch_likely(&switch_to_cond_stibp)) {

Quoted 2 lines

So if we are aiming to optimize for "fixed" or unaffected hardware, maybe we should modify the likely hint to unlikely then.

Right, I think that makes sense, Thomas?