linux-kernel - [PATCH v4 07/11] x86/vmscape: Use write_ibpb() instead of indirect_branch_prediction

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Message-ID: <20251119-vmscape-bhb-v4-7-1adad4e69ddc@linux.intel.com>
Date: Wed, 19 Nov 2025 22:19:19 -0800
From: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To: x86@...nel.org, David Kaplan <david.kaplan@....com>,
	Nikolay Borisov <nik.borisov@...e.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Sean Christopherson <seanjc@...gle.com>,
	Paolo Bonzini <pbonzini@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Asit Mallick <asit.k.mallick@...el.com>,
	Tao Zhang <tao1.zhang@...el.com>
Subject: [PATCH v4 07/11] x86/vmscape: Use write_ibpb() instead of
 indirect_branch_prediction_barrier()

indirect_branch_prediction_barrier() is a wrapper to write_ibpb(), which
also checks if the CPU supports IBPB. For VMSCAPE, call to
indirect_branch_prediction_barrier() is only possible when CPU supports
IBPB.

Simply call write_ibpb() directly to avoid unnecessary alternative
patching.

Suggested-by: Dave Hansen <dave.hansen@...ux.intel.com>
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
---
 arch/x86/include/asm/entry-common.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/entry-common.h b/arch/x86/include/asm/entry-common.h
index c45858db16c92fc1364fb818185fba7657840991..78b143673ca72642149eb2dbf3e3e31370fe6b28 100644
--- a/arch/x86/include/asm/entry-common.h
+++ b/arch/x86/include/asm/entry-common.h
@@ -97,7 +97,7 @@ static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs,
 	/* Avoid unnecessary reads of 'x86_predictor_flush_exit_to_user' */
 	if (cpu_feature_enabled(X86_FEATURE_IBPB_EXIT_TO_USER) &&
 	    this_cpu_read(x86_predictor_flush_exit_to_user)) {
-		indirect_branch_prediction_barrier();
+		write_ibpb();
 		this_cpu_write(x86_predictor_flush_exit_to_user, false);
 	}
 }

-- 
2.34.1