linux-kernel - [PATCH] KVM: X86: Avoid explictly fetch instruction in x86_decode

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Message-Id: <20200304021637.17856-1-peterx@redhat.com>
Date:   Tue,  3 Mar 2020 21:16:37 -0500
From:   Peter Xu <peterx@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        peterx@...hat.com, Vitaly Kuznetsov <vkuznets@...hat.com>
Subject: [PATCH] KVM: X86: Avoid explictly fetch instruction in x86_decode_insn()

insn_fetch() will always implicitly refill instruction buffer properly
when the buffer is empty, so we don't need to explicitly fetch it even
if insn_len==0 for x86_decode_insn().

Signed-off-by: Peter Xu <peterx@...hat.com>
---
 arch/x86/kvm/emulate.c | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index dd19fb3539e0..04f33c1ca926 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -5175,11 +5175,6 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len)
 	ctxt->opcode_len = 1;
 	if (insn_len > 0)
 		memcpy(ctxt->fetch.data, insn, insn_len);
-	else {
-		rc = __do_insn_fetch_bytes(ctxt, 1);
-		if (rc != X86EMUL_CONTINUE)
-			goto done;
-	}
 
 	switch (mode) {
 	case X86EMUL_MODE_REAL:
-- 
2.24.1