linux-kernel - [PATCH 1/2] x86/msr: Rename the WRMSRNS opcode macro to ASM

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Message-ID: <20250227010111.3222742-2-seanjc@google.com>
Date: Wed, 26 Feb 2025 17:01:10 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, Xin Li <xin@...or.com>
Subject: [PATCH 1/2] x86/msr: Rename the WRMSRNS opcode macro to ASM_WRMSRNS
 (for KVM)

Rename the WRMSRNS instruction opcode macro so that it doesn't collide
with X86_FEATURE_WRMSRNS when using token pasting to generate references
to X86_FEATURE_WRMSRNS.  KVM heavily uses token pasting to generate KVM's
set of support feature bits, and adding WRMSRNS support in KVM will run
will run afoul of the opcode macro.

  arch/x86/kvm/cpuid.c:719:37: error: pasting "X86_FEATURE_" and "" "" does not
                                      give a valid preprocessing token
  719 |         u32 __leaf = __feature_leaf(X86_FEATURE_##name);                \
      |                                     ^~~~~~~~~~~~

KVM has worked around one such collision in the past by #undef'ing the
problematic macro in order to avoid blocking a KVM rework, but such games
are generally undesirable, e.g. requires bleeding macro details into KVM,
risks weird behavior if what KVM is #undef'ing changes, etc.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/include/asm/msr.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/msr.h b/arch/x86/include/asm/msr.h
index 001853541f1e..60b80a36d045 100644
--- a/arch/x86/include/asm/msr.h
+++ b/arch/x86/include/asm/msr.h
@@ -300,7 +300,7 @@ do {							\
 #endif	/* !CONFIG_PARAVIRT_XXL */
 
 /* Instruction opcode for WRMSRNS supported in binutils >= 2.40 */
-#define WRMSRNS _ASM_BYTES(0x0f,0x01,0xc6)
+#define ASM_WRMSRNS _ASM_BYTES(0x0f,0x01,0xc6)
 
 /* Non-serializing WRMSR, when available.  Falls back to a serializing WRMSR. */
 static __always_inline void wrmsrns(u32 msr, u64 val)
@@ -309,7 +309,7 @@ static __always_inline void wrmsrns(u32 msr, u64 val)
 	 * WRMSR is 2 bytes.  WRMSRNS is 3 bytes.  Pad WRMSR with a redundant
 	 * DS prefix to avoid a trailing NOP.
 	 */
-	asm volatile("1: " ALTERNATIVE("ds wrmsr", WRMSRNS, X86_FEATURE_WRMSRNS)
+	asm volatile("1: " ALTERNATIVE("ds wrmsr", ASM_WRMSRNS, X86_FEATURE_WRMSRNS)
 		     "2: " _ASM_EXTABLE_TYPE(1b, 2b, EX_TYPE_WRMSR)
 		     : : "c" (msr), "a" ((u32)val), "d" ((u32)(val >> 32)));
 }
-- 
2.48.1.711.g2feabab25a-goog