linux-kernel - [PATCH v2 1/4] KVM: x86: Factor out x86 instruction emulation with decoding

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Date:   Thu, 21 Jan 2021 01:55:05 -0500
From:   Wei Huang <wei.huang2@....com>
To:     kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, pbonzini@...hat.com,
        vkuznets@...hat.com, mlevitsk@...hat.com, seanjc@...gle.com,
        joro@...tes.org, bp@...en8.de, tglx@...utronix.de,
        mingo@...hat.com, x86@...nel.org, jmattson@...gle.com,
        wanpengli@...cent.com, bsd@...hat.com, dgilbert@...hat.com,
        luto@...capital.net, wei.huang2@....com
Subject: [PATCH v2 1/4] KVM: x86: Factor out x86 instruction emulation with decoding

Move the instruction decode part out of x86_emulate_instruction() for it
to be used in other places. Also kvm_clear_exception_queue() is moved
inside the if-statement as it doesn't apply when KVM are coming back from
userspace.

Co-developed-by: Bandan Das <bsd@...hat.com>
Signed-off-by: Bandan Das <bsd@...hat.com>
Signed-off-by: Wei Huang <wei.huang2@....com>
---
 arch/x86/kvm/x86.c | 63 +++++++++++++++++++++++++++++-----------------
 arch/x86/kvm/x86.h |  2 ++
 2 files changed, 42 insertions(+), 23 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 9a8969a6dd06..580883cee493 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7298,6 +7298,43 @@ static bool is_vmware_backdoor_opcode(struct x86_emulate_ctxt *ctxt)
 	return false;
 }
 
+/*
+ * Decode and emulate instruction. Return EMULATION_OK if success.
+ */
+int x86_emulate_decoded_instruction(struct kvm_vcpu *vcpu, int emulation_type,
+				    void *insn, int insn_len)
+{
+	int r = EMULATION_OK;
+	struct x86_emulate_ctxt *ctxt = vcpu->arch.emulate_ctxt;
+
+	init_emulate_ctxt(vcpu);
+
+	/*
+	 * We will reenter on the same instruction since
+	 * we do not set complete_userspace_io.  This does not
+	 * handle watchpoints yet, those would be handled in
+	 * the emulate_ops.
+	 */
+	if (!(emulation_type & EMULTYPE_SKIP) &&
+	    kvm_vcpu_check_breakpoint(vcpu, &r))
+		return r;
+
+	ctxt->interruptibility = 0;
+	ctxt->have_exception = false;
+	ctxt->exception.vector = -1;
+	ctxt->perm_ok = false;
+
+	ctxt->ud = emulation_type & EMULTYPE_TRAP_UD;
+
+	r = x86_decode_insn(ctxt, insn, insn_len);
+
+	trace_kvm_emulate_insn_start(vcpu);
+	++vcpu->stat.insn_emulation;
+
+	return r;
+}
+EXPORT_SYMBOL_GPL(x86_emulate_decoded_instruction);
+
 int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 			    int emulation_type, void *insn, int insn_len)
 {
@@ -7317,32 +7354,12 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 	 */
 	write_fault_to_spt = vcpu->arch.write_fault_to_shadow_pgtable;
 	vcpu->arch.write_fault_to_shadow_pgtable = false;
-	kvm_clear_exception_queue(vcpu);
 
 	if (!(emulation_type & EMULTYPE_NO_DECODE)) {
-		init_emulate_ctxt(vcpu);
-
-		/*
-		 * We will reenter on the same instruction since
-		 * we do not set complete_userspace_io.  This does not
-		 * handle watchpoints yet, those would be handled in
-		 * the emulate_ops.
-		 */
-		if (!(emulation_type & EMULTYPE_SKIP) &&
-		    kvm_vcpu_check_breakpoint(vcpu, &r))
-			return r;
-
-		ctxt->interruptibility = 0;
-		ctxt->have_exception = false;
-		ctxt->exception.vector = -1;
-		ctxt->perm_ok = false;
-
-		ctxt->ud = emulation_type & EMULTYPE_TRAP_UD;
-
-		r = x86_decode_insn(ctxt, insn, insn_len);
+		kvm_clear_exception_queue(vcpu);
 
-		trace_kvm_emulate_insn_start(vcpu);
-		++vcpu->stat.insn_emulation;
+		r = x86_emulate_decoded_instruction(vcpu, emulation_type,
+						    insn, insn_len);
 		if (r != EMULATION_OK)  {
 			if ((emulation_type & EMULTYPE_TRAP_UD) ||
 			    (emulation_type & EMULTYPE_TRAP_UD_FORCED)) {
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index c5ee0f5ce0f1..fc42454a4c27 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -273,6 +273,8 @@ bool kvm_mtrr_check_gfn_range_consistency(struct kvm_vcpu *vcpu, gfn_t gfn,
 					  int page_num);
 bool kvm_vector_hashing_enabled(void);
 void kvm_fixup_and_inject_pf_error(struct kvm_vcpu *vcpu, gva_t gva, u16 error_code);
+int x86_emulate_decoded_instruction(struct kvm_vcpu *vcpu, int emulation_type,
+				    void *insn, int insn_len);
 int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 			    int emulation_type, void *insn, int insn_len);
 fastpath_t handle_fastpath_set_msr_irqoff(struct kvm_vcpu *vcpu);
-- 
2.27.0