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From:   Anup Patel <apatel@ventanamicro.com>
Date:   Mon, 11 Jul 2022 09:46:19 +0530
Message-ID: <CAK9=C2UjJ8eqXSBzsbpdUn9E=5_6Zp2NAnHts_FaGpxWxN-Krw@mail.gmail.com>
Subject: Re: [PATCH] RISC-V: KVM: Fix SRCU deadlock caused by kvm_riscv_check_vcpu_requests()
To:     Paolo Bonzini <pbonzini@redhat.com>,
        Atish Patra <atishp@atishpatra.org>
Cc:     Palmer Dabbelt <palmer@dabbelt.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Alistair Francis <Alistair.Francis@wdc.com>,
        Bin Meng <bmeng.cn@gmail.com>,
        Heinrich Schuchardt <heinrich.schuchardt@canonical.com>,
        Anup Patel <anup@brainfault.org>,
        KVM General <kvm@vger.kernel.org>,
        "open list:KERNEL VIRTUAL MACHINE FOR RISC-V (KVM/riscv)" 
        <kvm-riscv@lists.infradead.org>,
        linux-riscv <linux-riscv@lists.infradead.org>,
        "linux-kernel@vger.kernel.org List" <linux-kernel@vger.kernel.org>
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On Sun, Jul 10, 2022 at 8:41 PM Anup Patel <apatel@ventanamicro.com> 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")
> Reported-by: Bin Meng <bmeng.cn@gmail.com>
> Signed-off-by: Anup Patel <apatel@ventanamicro.com>

Thanks everyone for providing Tested-by and Reviewed-by.

I have queued this patch for 5.19-rcX fixes.

Regards,
Anup

> ---
>  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) {
>                                 /*
> --
> 2.34.1
>