linux-kernel - [PATCH v2] KVM:x86: Clean up ModR/M "reg" initialization in reg op decoding

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Date:   Thu,  8 Sep 2022 22:12:10 +0800
From:   Liam Ni <zhiguangni01@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org, x86@...nel.org
Cc:     pbonzini@...hat.com, tglx@...utronix.de,
        dave.hansen@...ux.intel.com, seanjc@...gle.com,
        zhiguangni01@...il.com
Subject: [PATCH v2] KVM:x86: Clean up ModR/M "reg" initialization in reg op decoding

From: Liam Ni <zhiguangni01@...il.com>

Refactor decode_register_operand() to get the ModR/M register if and
only if the instruction uses a ModR/M encoding to make it more obvious
how the register operand is retrieved.

Signed-off-by: Liam Ni <zhiguangni01@...il.com>
---
 arch/x86/kvm/emulate.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index f092c54d1a2f..879b52af763a 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -1137,9 +1137,11 @@ static int em_fnstsw(struct x86_emulate_ctxt *ctxt)
 static void decode_register_operand(struct x86_emulate_ctxt *ctxt,
 				    struct operand *op)
 {
-	unsigned reg = ctxt->modrm_reg;
+	unsigned int reg;
 
-	if (!(ctxt->d & ModRM))
+	if ((ctxt->d & ModRM))
+		reg = ctxt->modrm_reg;
+	else
 		reg = (ctxt->b & 7) | ((ctxt->rex_prefix & 1) << 3);
 
 	if (ctxt->d & Sse) {
-- 
2.34.1