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

[Sean Christopherson]

Decouple the use of ALTERNATIVE from the encoding of VERW to clear CPU
buffers so that KVM can use ALTERNATIVE_2 to handle "always clear buffers"
and "clear if guest can access host MMIO" in a single statement.

No functional change intended.

Reviewed-by: Brendan Jackman <jackmanb@xxxxxxxxxx>
Reviewed-by: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 arch/x86/include/asm/nospec-branch.h | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 08ed5a2e46a5..8b4885a1b2ef 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -308,24 +308,24 @@
  * CFLAGS.ZF.
  * Note: Only the memory operand variant of VERW clears the CPU buffers.
  */
-.macro __CLEAR_CPU_BUFFERS feature
 #ifdef CONFIG_X86_64
-	ALTERNATIVE "", "verw x86_verw_sel(%rip)", \feature
+#define VERW	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).
-	 */
-	ALTERNATIVE "", "verw %cs:x86_verw_sel", \feature
+/*
+ * 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
 #endif
-.endm
 
+#define __CLEAR_CPU_BUFFERS	__stringify(VERW)
+
+/* If necessary, emit VERW on exit-to-userspace to clear CPU buffers. */
 #define CLEAR_CPU_BUFFERS \
-	__CLEAR_CPU_BUFFERS X86_FEATURE_CLEAR_CPU_BUF
+	ALTERNATIVE "", __CLEAR_CPU_BUFFERS, X86_FEATURE_CLEAR_CPU_BUF
 
 #define VM_CLEAR_CPU_BUFFERS \
-	__CLEAR_CPU_BUFFERS X86_FEATURE_CLEAR_CPU_BUF_VM
+	ALTERNATIVE "", __CLEAR_CPU_BUFFERS, X86_FEATURE_CLEAR_CPU_BUF_VM
 
 #ifdef CONFIG_X86_64
 .macro CLEAR_BRANCH_HISTORY
-- 
2.52.0.rc1.455.g30608eb744-goog