Re: [PATCH] RISC-V: KVM: Fix SRCU deadlock caused by kvm_riscv_check_vcpu_requests()

[Bin Meng]

On Sun, Jul 10, 2022 at 11:11 PM Anup Patel <apatel@xxxxxxxxxxxxxxxx> wrote:
>
> 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")

nites: the "Fixes" tag should be put in a single line to avoid
breaking scripts that parse the "Fixes" tag

> Reported-by: Bin Meng <bmeng.cn@xxxxxxxxx>
> Signed-off-by: Anup Patel <apatel@xxxxxxxxxxxxxxxx>
> ---
>  arch/riscv/kvm/vcpu.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
> index b7a433c54d0f..5d271b597613 100644
> --- a/arch/riscv/kvm/vcpu.c
> +++ b/arch/riscv/kvm/vcpu.c
> @@ -845,9 +845,11 @@ 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) {
>                                 /*
> --

Tested-by: Bin Meng <bmeng.cn@xxxxxxxxx>