linux-kernel - [RFC PATCH 09/16] RISC-V: KVM: Handle WFI exits for VCPU

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Date:   Mon, 29 Jul 2019 11:57:17 +0000
From:   Anup Patel <Anup.Patel@....com>
To:     Palmer Dabbelt <palmer@...ive.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim K <rkrcmar@...hat.com>
CC:     Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Atish Patra <Atish.Patra@....com>,
        Alistair Francis <Alistair.Francis@....com>,
        Damien Le Moal <Damien.LeMoal@....com>,
        Christoph Hellwig <hch@...radead.org>,
        Anup Patel <anup@...infault.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Anup Patel <Anup.Patel@....com>
Subject: [RFC PATCH 09/16] 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@....com>
---
 arch/riscv/kvm/vcpu_exit.c | 86 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 86 insertions(+)

diff --git a/arch/riscv/kvm/vcpu_exit.c b/arch/riscv/kvm/vcpu_exit.c
index 4dafefa59338..2d09640c98b2 100644
--- a/arch/riscv/kvm/vcpu_exit.c
+++ b/arch/riscv/kvm/vcpu_exit.c
@@ -12,6 +12,9 @@
 #include <linux/kvm_host.h>
 #include <asm/csr.h>
 
+#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
@@ -178,6 +181,85 @@ static ulong get_insn(struct kvm_vcpu *vcpu)
 	return val;
 }
 
+typedef int (*illegal_insn_func)(struct kvm_vcpu *vcpu,
+				 struct kvm_run *run,
+				 ulong insn);
+
+static int truly_illegal_insn(struct kvm_vcpu *vcpu,
+			      struct kvm_run *run,
+			      ulong insn)
+{
+	/* TODO: Redirect trap to Guest VCPU */
+	return -ENOTSUPP;
+}
+
+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_riscv_vcpu_has_interrupt(vcpu)) {
+			kvm_vcpu_block(vcpu);
+			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 illegal_insn_func illegal_insn_table[32] = {
+	truly_illegal_insn, /* 0 */
+	truly_illegal_insn, /* 1 */
+	truly_illegal_insn, /* 2 */
+	truly_illegal_insn, /* 3 */
+	truly_illegal_insn, /* 4 */
+	truly_illegal_insn, /* 5 */
+	truly_illegal_insn, /* 6 */
+	truly_illegal_insn, /* 7 */
+	truly_illegal_insn, /* 8 */
+	truly_illegal_insn, /* 9 */
+	truly_illegal_insn, /* 10 */
+	truly_illegal_insn, /* 11 */
+	truly_illegal_insn, /* 12 */
+	truly_illegal_insn, /* 13 */
+	truly_illegal_insn, /* 14 */
+	truly_illegal_insn, /* 15 */
+	truly_illegal_insn, /* 16 */
+	truly_illegal_insn, /* 17 */
+	truly_illegal_insn, /* 18 */
+	truly_illegal_insn, /* 19 */
+	truly_illegal_insn, /* 20 */
+	truly_illegal_insn, /* 21 */
+	truly_illegal_insn, /* 22 */
+	truly_illegal_insn, /* 23 */
+	truly_illegal_insn, /* 24 */
+	truly_illegal_insn, /* 25 */
+	truly_illegal_insn, /* 26 */
+	truly_illegal_insn, /* 27 */
+	system_opcode_insn, /* 28 */
+	truly_illegal_insn, /* 29 */
+	truly_illegal_insn, /* 30 */
+	truly_illegal_insn  /* 31 */
+};
+
+static int illegal_inst_fault(struct kvm_vcpu *vcpu, struct kvm_run *run,
+			      unsigned long stval)
+{
+	ulong insn = stval;
+
+	if (unlikely((insn & 3) != 3)) {
+		if (insn == 0)
+			insn = get_insn(vcpu);
+		if ((insn & 3) != 3)
+			return truly_illegal_insn(vcpu, run, insn);
+	}
+
+	return illegal_insn_table[(insn & 0x7c) >> 2](vcpu, run, insn);
+}
+
 static int emulate_load(struct kvm_vcpu *vcpu, struct kvm_run *run,
 			unsigned long fault_addr)
 {
@@ -438,6 +520,10 @@ int kvm_riscv_vcpu_exit(struct kvm_vcpu *vcpu, struct kvm_run *run,
 	ret = -EFAULT;
 	run->exit_reason = KVM_EXIT_UNKNOWN;
 	switch (scause) {
+	case EXC_INST_ILLEGAL:
+		if (vcpu->arch.guest_context.hstatus & HSTATUS_SPV)
+			ret = illegal_inst_fault(vcpu, run, stval);
+		break;
 	case EXC_INST_PAGE_FAULT:
 	case EXC_LOAD_PAGE_FAULT:
 	case EXC_STORE_PAGE_FAULT:
-- 
2.17.1