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.pa...@wdc.com>
Acked-by: Paolo Bonzini <pbonz...@redhat.com>
Reviewed-by: Paolo Bonzini <pbonz...@redhat.com>
---
 arch/riscv/kvm/vcpu_exit.c | 76 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 76 insertions(+)

diff --git a/arch/riscv/kvm/vcpu_exit.c b/arch/riscv/kvm/vcpu_exit.c
index 7fd603acd97a..6ef833e29e71 100644
--- a/arch/riscv/kvm/vcpu_exit.c
+++ b/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          0xffffff00
+#define INSN_MATCH_WFI         0x10500000
+
 #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)
 {
@@ -565,6 +637,10 @@ 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:
-- 
2.25.1

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