RISC-V: KVM: Handle WFI exits for VCPU

We get illegal instruction trap whenever Guest/VM executes WFI
instruction.

This patch handles WFI trap by blocking the trapped VCPU using
kvm_vcpu_block() API. The blocked VCPU will be automatically
resumed whenever a VCPU interrupt is injected from user-space
or from in-kernel IRQCHIP emulation.
Signed-off-by: Anup Patel <anup.patel@wdc.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Palmer Dabbelt <palmerdabbelt@google.com>

arch/riscv/kvm/vcpu_exit.c

@@ -12,6 +12,13 @@
 #include <linux/kvm_host.h>
 #include <asm/csr.h>
 
+#define INSN_OPCODE_MASK	0x007c
+#define INSN_OPCODE_SHIFT	2
+#define INSN_OPCODE_SYSTEM	28
+
+#define INSN_MASK_WFI		0xffffffff
+#define INSN_MATCH_WFI		0x10500073
+
 #define INSN_MATCH_LB		0x3
 #define INSN_MASK_LB		0x707f
 #define INSN_MATCH_LH		0x1003
@@ -116,6 +123,71 @@
 				 (s32)(((insn) >> 7) & 0x1f))
 #define MASK_FUNCT3		0x7000
 
+static int truly_illegal_insn(struct kvm_vcpu *vcpu,
+			      struct kvm_run *run,
+			      ulong insn)
+{
+	struct kvm_cpu_trap utrap = { 0 };
+
+	/* Redirect trap to Guest VCPU */
+	utrap.sepc = vcpu->arch.guest_context.sepc;
+	utrap.scause = EXC_INST_ILLEGAL;
+	utrap.stval = insn;
+	kvm_riscv_vcpu_trap_redirect(vcpu, &utrap);
+
+	return 1;
+}
+
+static int system_opcode_insn(struct kvm_vcpu *vcpu,
+			      struct kvm_run *run,
+			      ulong insn)
+{
+	if ((insn & INSN_MASK_WFI) == INSN_MATCH_WFI) {
+		vcpu->stat.wfi_exit_stat++;
+		if (!kvm_arch_vcpu_runnable(vcpu)) {
+			srcu_read_unlock(&vcpu->kvm->srcu, vcpu->arch.srcu_idx);
+			kvm_vcpu_block(vcpu);
+			vcpu->arch.srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
+			kvm_clear_request(KVM_REQ_UNHALT, vcpu);
+		}
+		vcpu->arch.guest_context.sepc += INSN_LEN(insn);
+		return 1;
+	}
+
+	return truly_illegal_insn(vcpu, run, insn);
+}
+
+static int virtual_inst_fault(struct kvm_vcpu *vcpu, struct kvm_run *run,
+			      struct kvm_cpu_trap *trap)
+{
+	unsigned long insn = trap->stval;
+	struct kvm_cpu_trap utrap = { 0 };
+	struct kvm_cpu_context *ct;
+
+	if (unlikely(INSN_IS_16BIT(insn))) {
+		if (insn == 0) {
+			ct = &vcpu->arch.guest_context;
+			insn = kvm_riscv_vcpu_unpriv_read(vcpu, true,
+							  ct->sepc,
+							  &utrap);
+			if (utrap.scause) {
+				utrap.sepc = ct->sepc;
+				kvm_riscv_vcpu_trap_redirect(vcpu, &utrap);
+				return 1;
+			}
+		}
+		if (INSN_IS_16BIT(insn))
+			return truly_illegal_insn(vcpu, run, insn);
+	}
+
+	switch ((insn & INSN_OPCODE_MASK) >> INSN_OPCODE_SHIFT) {
+	case INSN_OPCODE_SYSTEM:
+		return system_opcode_insn(vcpu, run, insn);
+	default:
+		return truly_illegal_insn(vcpu, run, insn);
+	}
+}
+
 static int emulate_load(struct kvm_vcpu *vcpu, struct kvm_run *run,
 			unsigned long fault_addr, unsigned long htinst)
 {
@@ -596,6 +668,10 @@ int kvm_riscv_vcpu_exit(struct kvm_vcpu *vcpu, struct kvm_run *run,
 	ret = -EFAULT;
 	run->exit_reason = KVM_EXIT_UNKNOWN;
 	switch (trap->scause) {
+	case EXC_VIRTUAL_INST_FAULT:
+		if (vcpu->arch.guest_context.hstatus & HSTATUS_SPV)
+			ret = virtual_inst_fault(vcpu, run, trap);
+		break;
 	case EXC_INST_GUEST_PAGE_FAULT:
 	case EXC_LOAD_GUEST_PAGE_FAULT:
 	case EXC_STORE_GUEST_PAGE_FAULT: