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From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
To: x86@kernel.org, David Kaplan <david.kaplan@amd.com>,
	Nikolay Borisov <nik.borisov@suse.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Josh Poimboeuf <jpoimboe@kernel.org>,
	Sean Christopherson <seanjc@google.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
	Asit Mallick <asit.k.mallick@intel.com>,
	Tao Zhang <tao1.zhang@intel.com>
Subject: [PATCH v5 5/9] x86/vmscape: Use write_ibpb() instead of indirect_branch_prediction_barrier()
Date: Wed, 26 Nov 2025 14:15:55 -0800	[thread overview]
Message-ID: <20251126-vmscape-bhb-v5-5-02d66e423b00@linux.intel.com> (raw)
In-Reply-To: <20251126-vmscape-bhb-v5-0-02d66e423b00@linux.intel.com>

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@linux.intel.com>
Reviewed-by: Nikolay Borisov <nik.borisov@suse.com>
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.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



  parent reply	other threads:[~2025-11-26 22:15 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-11-26 22:14 [PATCH v5 0/9] VMSCAPE optimization for BHI variant Pawan Gupta
2025-11-26 22:14 ` [PATCH v5 1/9] x86/bhi: x86/vmscape: Move LFENCE out of clear_bhb_loop() Pawan Gupta
2025-11-26 22:15 ` [PATCH v5 2/9] x86/bhi: Make clear_bhb_loop() effective on newer CPUs Pawan Gupta
2025-11-26 22:15 ` [PATCH v5 3/9] x86/vmscape: Rename x86_ibpb_exit_to_user to x86_predictor_flush_exit_to_user Pawan Gupta
2025-11-26 22:15 ` [PATCH v5 4/9] x86/vmscape: Move mitigation selection to a switch() Pawan Gupta
2025-11-27  1:04   ` kernel test robot
2025-11-29 19:35   ` kernel test robot
2025-11-26 22:15 ` Pawan Gupta [this message]
2025-11-26 22:16 ` [PATCH v5 6/9] x86/vmscape: Use static_call() for predictor flush Pawan Gupta
2025-11-26 22:16 ` [PATCH v5 7/9] x86/vmscape: Deploy BHB clearing mitigation Pawan Gupta
2025-11-26 22:16 ` [PATCH v5 8/9] x86/vmscape: Fix conflicting attack-vector controls with =force Pawan Gupta
2025-11-26 22:16 ` [PATCH v5 9/9] x86/vmscape: Add cmdline vmscape=on to override attack vector controls Pawan Gupta

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