linux-kernel - [PATCH 2/6] x86/mm: Remove X86_FEATURE_USE_IBPB checks in cond

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Message-ID: <20250219220826.2453186-3-yosry.ahmed@linux.dev>
Date: Wed, 19 Feb 2025 22:08:22 +0000
From: Yosry Ahmed <yosry.ahmed@...ux.dev>
To: x86@...nel.org
Cc: Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
	Andy Lutomirski <luto@...nel.org>,
	Sean Christopherson <seanjc@...gle.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 2/6] x86/mm: Remove X86_FEATURE_USE_IBPB checks in cond_mitigation()

The check is performed when either switch_mm_cond_ibpb or
switch_mm_always_ibpb is set. In both cases, X86_FEATURE_USE_IBPB is
always set. Remove the redundant check.

Signed-off-by: Yosry Ahmed <yosry.ahmed@...ux.dev>
---
 arch/x86/mm/tlb.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index be0c1a509869c..e860fc8edfae4 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -437,8 +437,7 @@ static void cond_mitigation(struct task_struct *next)
 		 * both have the IBPB bit set.
 		 */
 		if (next_mm != prev_mm &&
-		    (next_mm | prev_mm) & LAST_USER_MM_IBPB &&
-		    cpu_feature_enabled(X86_FEATURE_USE_IBPB))
+		    (next_mm | prev_mm) & LAST_USER_MM_IBPB)
 			indirect_branch_prediction_barrier();
 	}
 
@@ -448,8 +447,7 @@ static void cond_mitigation(struct task_struct *next)
 		 * different context than the user space task which ran
 		 * last on this CPU.
 		 */
-		if ((prev_mm & ~LAST_USER_MM_SPEC_MASK) != (unsigned long)next->mm &&
-		    cpu_feature_enabled(X86_FEATURE_USE_IBPB))
+		if ((prev_mm & ~LAST_USER_MM_SPEC_MASK) != (unsigned long)next->mm)
 			indirect_branch_prediction_barrier();
 	}
 
-- 
2.48.1.601.g30ceb7b040-goog