RISC-V: KVM: Fix SRCU deadlock caused by kvm_riscv_check_vcpu_requests()

The kvm_riscv_check_vcpu_requests() is called with SRCU read lock held
and for KVM_REQ_SLEEP request it will block the VCPU without releasing
SRCU read lock. This causes KVM ioctls (such as KVM_IOEVENTFD) from
other VCPUs of the same Guest/VM to hang/deadlock if there is any
synchronize_srcu() or synchronize_srcu_expedited() in the path.

To fix the above in kvm_riscv_check_vcpu_requests(), we should do SRCU
read unlock before blocking the VCPU and do SRCU read lock after VCPU
wakeup.

Fixes: cce69aff689e ("RISC-V: KVM: Implement VCPU interrupts and requests handling")
Reported-by: Bin Meng <bmeng.cn@gmail.com>
Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Tested-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>
Signed-off-by: Anup Patel <anup@brainfault.org>

diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
index 7f4ad5e4373a9d72a9f1cd6acb962a4a929c9f9c..f3455dc013fa0cd8dfefd7a7116477c510985cf7 100644 (file)
--- a/arch/riscv/kvm/vcpu.c
+++ b/arch/riscv/kvm/vcpu.c
@@ -781,9 +781,11 @@ static void kvm_riscv_check_vcpu_requests(struct kvm_vcpu *vcpu)
 
        if (kvm_request_pending(vcpu)) {
                if (kvm_check_request(KVM_REQ_SLEEP, vcpu)) {
+                       kvm_vcpu_srcu_read_unlock(vcpu);
                        rcuwait_wait_event(wait,
                                (!vcpu->arch.power_off) && (!vcpu->arch.pause),
                                TASK_INTERRUPTIBLE);
+                       kvm_vcpu_srcu_read_lock(vcpu);
 
                        if (vcpu->arch.power_off || vcpu->arch.pause) {
                                /*