linux-kernel - Re: [PATCH v5 3/9] x86/bugs: Decouple ALTERNATIVE usage from VERW macro definition

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Message-ID: <20251117101129.GGaRr00XgEln3XzR5N@fat_crate.local>
Date: Mon, 17 Nov 2025 11:11:29 +0100
From: Borislav Petkov <bp@...en8.de>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Josh Poimboeuf <jpoimboe@...nel.org>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
	Brendan Jackman <jackmanb@...gle.com>
Subject: Re: [PATCH v5 3/9] x86/bugs: Decouple ALTERNATIVE usage from VERW
 macro definition

On Thu, Nov 13, 2025 at 03:37:40PM -0800, Sean Christopherson wrote:
> +#define __CLEAR_CPU_BUFFERS	__stringify(VERW)

Let's get rid of one indirection level pls:

diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 8b4885a1b2ef..59945cb5e5f9 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -309,23 +309,21 @@
  * Note: Only the memory operand variant of VERW clears the CPU buffers.
  */
 #ifdef CONFIG_X86_64
-#define VERW	verw x86_verw_sel(%rip)
+#define VERW	__stringify(verw x86_verw_sel(%rip))
 #else
 /*
  * In 32bit mode, the memory operand must be a %cs reference. The data segments
  * may not be usable (vm86 mode), and the stack segment may not be flat (ESPFIX32).
  */
-#define VERW	verw %cs:x86_verw_sel
+#define VERW	__stringify(verw %cs:x86_verw_sel)
 #endif
 
-#define __CLEAR_CPU_BUFFERS	__stringify(VERW)
-
 /* If necessary, emit VERW on exit-to-userspace to clear CPU buffers. */
 #define CLEAR_CPU_BUFFERS \
-	ALTERNATIVE "", __CLEAR_CPU_BUFFERS, X86_FEATURE_CLEAR_CPU_BUF
+	ALTERNATIVE "", VERW, X86_FEATURE_CLEAR_CPU_BUF
 
 #define VM_CLEAR_CPU_BUFFERS \
-	ALTERNATIVE "", __CLEAR_CPU_BUFFERS, X86_FEATURE_CLEAR_CPU_BUF_VM
+	ALTERNATIVE "", VERW, X86_FEATURE_CLEAR_CPU_BUF_VM
 
 #ifdef CONFIG_X86_64
 .macro CLEAR_BRANCH_HISTORY

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette