KVM: x86: Refactor can_emulate_instruction() return to be more expressive

Refactor and rename can_emulate_instruction() to allow vendor code to
return more than true/false, e.g. to explicitly differentiate between
"retry", "fault", and "unhandleable".  For now, just do the plumbing, a
future patch will expand SVM's implementation to signal outright failure
if KVM attempts EMULTYPE_SKIP on an SEV guest.

No functional change intended (or rather, none that are visible to the
guest or userspace).

Link: https://lore.kernel.org/r/20230825013621.2845700-4-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

1 files changed, 17 insertions, 14 deletions

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index f36a6d819280..c4e700f945f8 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -364,8 +364,8 @@ static void svm_set_interrupt_shadow(struct kvm_vcpu *vcpu, int mask)
 		svm->vmcb->control.int_state |= SVM_INTERRUPT_SHADOW_MASK;
 
 }
-static bool svm_can_emulate_instruction(struct kvm_vcpu *vcpu, int emul_type,
-					void *insn, int insn_len);
+static int svm_check_emulate_instruction(struct kvm_vcpu *vcpu, int emul_type,
+					 void *insn, int insn_len);
 
 static int __svm_skip_emulated_instruction(struct kvm_vcpu *vcpu,
 					   bool commit_side_effects)
@@ -391,7 +391,7 @@ static int __svm_skip_emulated_instruction(struct kvm_vcpu *vcpu,
 		 * right thing and treats "can't emulate" as outright failure
 		 * for EMULTYPE_SKIP.
 		 */
-		if (!svm_can_emulate_instruction(vcpu, EMULTYPE_SKIP, NULL, 0))
+		if (svm_check_emulate_instruction(vcpu, EMULTYPE_SKIP, NULL, 0) != X86EMUL_CONTINUE)
 			return 0;
 
 		if (unlikely(!commit_side_effects))
@@ -4727,15 +4727,15 @@ static void svm_enable_smi_window(struct kvm_vcpu *vcpu)
 }
 #endif
 
-static bool svm_can_emulate_instruction(struct kvm_vcpu *vcpu, int emul_type,
-					void *insn, int insn_len)
+static int svm_check_emulate_instruction(struct kvm_vcpu *vcpu, int emul_type,
+					 void *insn, int insn_len)
 {
 	bool smep, smap, is_user;
 	u64 error_code;
 
 	/* Emulation is always possible when KVM has access to all guest state. */
 	if (!sev_guest(vcpu->kvm))
-		return true;
+		return X86EMUL_CONTINUE;
 
 	/* #UD and #GP should never be intercepted for SEV guests. */
 	WARN_ON_ONCE(emul_type & (EMULTYPE_TRAP_UD |
@@ -4747,14 +4747,14 @@ static bool svm_can_emulate_instruction(struct kvm_vcpu *vcpu, int emul_type,
 	 * to guest register state.
 	 */
 	if (sev_es_guest(vcpu->kvm))
-		return false;
+		return X86EMUL_RETRY_INSTR;
 
 	/*
 	 * Emulation is possible if the instruction is already decoded, e.g.
 	 * when completing I/O after returning from userspace.
 	 */
 	if (emul_type & EMULTYPE_NO_DECODE)
-		return true;
+		return X86EMUL_CONTINUE;
 
 	/*
 	 * Emulation is possible for SEV guests if and only if a prefilled
@@ -4780,9 +4780,11 @@ static bool svm_can_emulate_instruction(struct kvm_vcpu *vcpu, int emul_type,
 	 * success (and in practice it will work the vast majority of the time).
 	 */
 	if (unlikely(!insn)) {
-		if (!(emul_type & EMULTYPE_SKIP))
-			kvm_queue_exception(vcpu, UD_VECTOR);
-		return false;
+		if (emul_type & EMULTYPE_SKIP)
+			return X86EMUL_RETRY_INSTR;
+
+		kvm_queue_exception(vcpu, UD_VECTOR);
+		return X86EMUL_PROPAGATE_FAULT;
 	}
 
 	/*
@@ -4793,7 +4795,7 @@ static bool svm_can_emulate_instruction(struct kvm_vcpu *vcpu, int emul_type,
 	 * table used to translate CS:RIP resides in emulated MMIO.
 	 */
 	if (likely(insn_len))
-		return true;
+		return X86EMUL_CONTINUE;
 
 	/*
 	 * Detect and workaround Errata 1096 Fam_17h_00_0Fh.
@@ -4851,6 +4853,7 @@ static bool svm_can_emulate_instruction(struct kvm_vcpu *vcpu, int emul_type,
 			kvm_inject_gp(vcpu, 0);
 		else
 			kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
+		return X86EMUL_PROPAGATE_FAULT;
 	}
 
 resume_guest:
@@ -4868,7 +4871,7 @@ resume_guest:
 	 * doesn't explicitly define "ignored", i.e. doing nothing and letting
 	 * the guest spin is technically "ignoring" the access.
 	 */
-	return false;
+	return X86EMUL_RETRY_INSTR;
 }
 
 static bool svm_apic_init_signal_blocked(struct kvm_vcpu *vcpu)
@@ -5028,7 +5031,7 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {
 	.vm_copy_enc_context_from = sev_vm_copy_enc_context_from,
 	.vm_move_enc_context_from = sev_vm_move_enc_context_from,
 
-	.can_emulate_instruction = svm_can_emulate_instruction,
+	.check_emulate_instruction = svm_check_emulate_instruction,
 
 	.apic_init_signal_blocked = svm_apic_init_signal_blocked,