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

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>

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