linux-kernel - [PATCH RFC v1 15/20] KVM: x86: Reject EVEX-prefix instructions in the emulator

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Message-ID: <20251110180131.28264-16-chang.seok.bae@intel.com>
Date: Mon, 10 Nov 2025 18:01:26 +0000
From: "Chang S. Bae" <chang.seok.bae@...el.com>
To: kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: pbonzini@...hat.com,
	seanjc@...gle.com,
	chao.gao@...el.com,
	zhao1.liu@...el.com,
	chang.seok.bae@...el.com
Subject: [PATCH RFC v1 15/20] KVM: x86: Reject EVEX-prefix instructions in the emulator

Explicitly mark EVEX-prefixed opcodes (0x62) as unsupported, clarifying
current decoding behavior.

While new prefixes like REX2 extend GPR handling, EVEX emulation should
be addressed separately once after VEX support is implemented.

Signed-off-by: Chang S. Bae <chang.seok.bae@...el.com>
---
 arch/x86/kvm/emulate.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 03f8e007b14e..9bd61ea496e5 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -4952,8 +4952,8 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len, int
 	if (ctxt->d & ModRM)
 		ctxt->modrm = insn_fetch(u8, ctxt);
 
-	/* vex-prefix instructions are not implemented */
-	if (ctxt->opcode_len == 1 && (ctxt->b == 0xc5 || ctxt->b == 0xc4) &&
+	/* VEX and EVEX-prefixed instructions are not implemented */
+	if (ctxt->opcode_len == 1 && (ctxt->b == 0xc5 || ctxt->b == 0xc4 || ctxt->b == 0x62) &&
 	    (mode == X86EMUL_MODE_PROT64 || (ctxt->modrm & 0xc0) == 0xc0)) {
 		ctxt->d = NotImpl;
 	}
-- 
2.51.0