LoongArch: KVM: Protect kvm_io_bus_{read,write}() with SRCU

When we enable lockdep we get such a warning:

 =============================
 WARNING: suspicious RCU usage
 6.12.0-rc7+ #1891 Tainted: G        W
 -----------------------------
 arch/loongarch/kvm/../../../virt/kvm/kvm_main.c:5945 suspicious rcu_dereference_check() usage!
 other info that might help us debug this:
 rcu_scheduler_active = 2, debug_locks = 1
 1 lock held by qemu-system-loo/948:
  #0: 90000001184a00a8 (&vcpu->mutex){+.+.}-{4:4}, at: kvm_vcpu_ioctl+0xf4/0xe20 [kvm]
 stack backtrace:
 CPU: 2 UID: 0 PID: 948 Comm: qemu-system-loo Tainted: G        W          6.12.0-rc7+ #1891
 Tainted: [W]=WARN
 Hardware name: Loongson Loongson-3A5000-7A1000-1w-CRB/Loongson-LS3A5000-7A1000-1w-CRB, BIOS vUDK2018-LoongArch-V2.0.0-prebeta9 10/21/2022
 Stack : 0000000000000089 9000000005a0db9c 90000000071519c8 900000012c578000
         900000012c57b940 0000000000000000 900000012c57b948 9000000007e53788
         900000000815bcc8 900000000815bcc0 900000012c57b7b0 0000000000000001
         0000000000000001 4b031894b9d6b725 0000000005dec000 9000000100427b00
         00000000000003d2 0000000000000001 000000000000002d 0000000000000003
         0000000000000030 00000000000003b4 0000000005dec000 0000000000000000
         900000000806d000 9000000007e53788 00000000000000b4 0000000000000004
         0000000000000004 0000000000000000 0000000000000000 9000000107baf600
         9000000008916000 9000000007e53788 9000000005924778 000000001fe001e5
         00000000000000b0 0000000000000007 0000000000000000 0000000000071c1d
         ...
 Call Trace:
 [<9000000005924778>] show_stack+0x38/0x180
 [<90000000071519c4>] dump_stack_lvl+0x94/0xe4
 [<90000000059eb754>] lockdep_rcu_suspicious+0x194/0x240
 [<ffff80000221f47c>] kvm_io_bus_read+0x19c/0x1e0 [kvm]
 [<ffff800002225118>] kvm_emu_mmio_read+0xd8/0x440 [kvm]
 [<ffff8000022254bc>] kvm_handle_read_fault+0x3c/0xe0 [kvm]
 [<ffff80000222b3c8>] kvm_handle_exit+0x228/0x480 [kvm]

Fix it by protecting kvm_io_bus_{read,write}() with SRCU.

Cc: stable@vger.kernel.org
Reviewed-by: Bibo Mao <maobibo@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

Author: chenhuacai

arch/loongarch/kvm/exit.c

@@ -156,7 +156,7 @@ static int kvm_handle_csr(struct kvm_vcpu *vcpu, larch_inst inst)
 
 int kvm_emu_iocsr(larch_inst inst, struct kvm_run *run, struct kvm_vcpu *vcpu)
 {
-	int ret;
+	int idx, ret;
 	unsigned long *val;
 	u32 addr, rd, rj, opcode;
 
@@ -167,7 +167,6 @@ int kvm_emu_iocsr(larch_inst inst, struct kvm_run *run, struct kvm_vcpu *vcpu)
 	rj = inst.reg2_format.rj;
 	opcode = inst.reg2_format.opcode;
 	addr = vcpu->arch.gprs[rj];
-	ret = EMULATE_DO_IOCSR;
 	run->iocsr_io.phys_addr = addr;
 	run->iocsr_io.is_write = 0;
 	val = &vcpu->arch.gprs[rd];
@@ -207,20 +206,28 @@ int kvm_emu_iocsr(larch_inst inst, struct kvm_run *run, struct kvm_vcpu *vcpu)
 	}
 
 	if (run->iocsr_io.is_write) {
-		if (!kvm_io_bus_write(vcpu, KVM_IOCSR_BUS, addr, run->iocsr_io.len, val))
+		idx = srcu_read_lock(&vcpu->kvm->srcu);
+		ret = kvm_io_bus_write(vcpu, KVM_IOCSR_BUS, addr, run->iocsr_io.len, val);
+		srcu_read_unlock(&vcpu->kvm->srcu, idx);
+		if (ret == 0)
 			ret = EMULATE_DONE;
-		else
+		else {
+			ret = EMULATE_DO_IOCSR;
 			/* Save data and let user space to write it */
 			memcpy(run->iocsr_io.data, val, run->iocsr_io.len);
-
+		}
 		trace_kvm_iocsr(KVM_TRACE_IOCSR_WRITE, run->iocsr_io.len, addr, val);
 	} else {
-		if (!kvm_io_bus_read(vcpu, KVM_IOCSR_BUS, addr, run->iocsr_io.len, val))
+		idx = srcu_read_lock(&vcpu->kvm->srcu);
+		ret = kvm_io_bus_read(vcpu, KVM_IOCSR_BUS, addr, run->iocsr_io.len, val);
+		srcu_read_unlock(&vcpu->kvm->srcu, idx);
+		if (ret == 0)
 			ret = EMULATE_DONE;
-		else
+		else {
+			ret = EMULATE_DO_IOCSR;
 			/* Save register id for iocsr read completion */
 			vcpu->arch.io_gpr = rd;
-
+		}
 		trace_kvm_iocsr(KVM_TRACE_IOCSR_READ, run->iocsr_io.len, addr, NULL);
 	}
 
@@ -359,7 +366,7 @@ static int kvm_handle_gspr(struct kvm_vcpu *vcpu)
 
 int kvm_emu_mmio_read(struct kvm_vcpu *vcpu, larch_inst inst)
 {
-	int ret;
+	int idx, ret;
 	unsigned int op8, opcode, rd;
 	struct kvm_run *run = vcpu->run;
 
@@ -464,8 +471,10 @@ int kvm_emu_mmio_read(struct kvm_vcpu *vcpu, larch_inst inst)
 		 * it need not return to user space to handle the mmio
 		 * exception.
 		 */
+		idx = srcu_read_lock(&vcpu->kvm->srcu);
 		ret = kvm_io_bus_read(vcpu, KVM_MMIO_BUS, vcpu->arch.badv,
 				      run->mmio.len, &vcpu->arch.gprs[rd]);
+		srcu_read_unlock(&vcpu->kvm->srcu, idx);
 		if (!ret) {
 			update_pc(&vcpu->arch);
 			vcpu->mmio_needed = 0;
@@ -531,7 +540,7 @@ int kvm_complete_mmio_read(struct kvm_vcpu *vcpu, struct kvm_run *run)
 
 int kvm_emu_mmio_write(struct kvm_vcpu *vcpu, larch_inst inst)
 {
-	int ret;
+	int idx, ret;
 	unsigned int rd, op8, opcode;
 	unsigned long curr_pc, rd_val = 0;
 	struct kvm_run *run = vcpu->run;
@@ -631,7 +640,9 @@ int kvm_emu_mmio_write(struct kvm_vcpu *vcpu, larch_inst inst)
 		 * it need not return to user space to handle the mmio
 		 * exception.
 		 */
+		idx = srcu_read_lock(&vcpu->kvm->srcu);
 		ret = kvm_io_bus_write(vcpu, KVM_MMIO_BUS, vcpu->arch.badv, run->mmio.len, data);
+		srcu_read_unlock(&vcpu->kvm->srcu, idx);
 		if (!ret)
 			return EMULATE_DONE;
 

arch/loongarch/kvm/intc/ipi.c

@@ -98,7 +98,7 @@ static void write_mailbox(struct kvm_vcpu *vcpu, int offset, uint64_t data, int
 
 static int send_ipi_data(struct kvm_vcpu *vcpu, gpa_t addr, uint64_t data)
 {
-	int i, ret;
+	int i, idx, ret;
 	uint32_t val = 0, mask = 0;
 
 	/*
@@ -107,7 +107,9 @@ static int send_ipi_data(struct kvm_vcpu *vcpu, gpa_t addr, uint64_t data)
 	 */
 	if ((data >> 27) & 0xf) {
 		/* Read the old val */
+		idx = srcu_read_lock(&vcpu->kvm->srcu);
 		ret = kvm_io_bus_read(vcpu, KVM_IOCSR_BUS, addr, sizeof(val), &val);
+		srcu_read_unlock(&vcpu->kvm->srcu, idx);
 		if (unlikely(ret)) {
 			kvm_err("%s: : read date from addr %llx failed\n", __func__, addr);
 			return ret;
@@ -121,7 +123,9 @@ static int send_ipi_data(struct kvm_vcpu *vcpu, gpa_t addr, uint64_t data)
 		val &= mask;
 	}
 	val |= ((uint32_t)(data >> 32) & ~mask);
+	idx = srcu_read_lock(&vcpu->kvm->srcu);
 	ret = kvm_io_bus_write(vcpu, KVM_IOCSR_BUS, addr, sizeof(val), &val);
+	srcu_read_unlock(&vcpu->kvm->srcu, idx);
 	if (unlikely(ret))
 		kvm_err("%s: : write date to addr %llx failed\n", __func__, addr);