ACK: [SRU][J/allwinner-5.17][J/starfive-5.17][PATCH v2 1/1] RISC-V: KVM: Fix SRCU deadlock caused by kvm_riscv_check_vcpu_requests()

[Stefan Bader]

On 29.07.22 11:16, Emil Renner Berthing wrote:
> From: Anup Patel <apatel at ventanamicro.com>
> 
> BugLink: https://bugs.launchpad.net/bugs/1980594
> 
> 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 at gmail.com>
> Signed-off-by: Anup Patel <apatel at ventanamicro.com>
> Reviewed-by: Atish Patra <atishp at rivosinc.com>
> Tested-by: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>
> Tested-by: Bin Meng <bmeng.cn at gmail.com>
> Signed-off-by: Anup Patel <anup at brainfault.org>
> (backported from commit be82abe6a76ba8e76f25312566182b0f13c4fbf9)
> [esmil: open code the srcu lock/unlock that now has static inline wrappers]
> Signed-off-by: Emil Renner Berthing <emil.renner.berthing at canonical.com>
Acked-by: Stefan Bader <stefan.bader at canonical.com>
> ---
>   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 aad430668bb4..5c00a6526dca 100644
> --- a/arch/riscv/kvm/vcpu.c
> +++ b/arch/riscv/kvm/vcpu.c
> @@ -673,9 +673,11 @@ static void kvm_riscv_check_vcpu_requests(struct kvm_vcpu *vcpu)
>   
>   	if (kvm_request_pending(vcpu)) {
>   		if (kvm_check_request(KVM_REQ_SLEEP, vcpu)) {
> +			srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
>   			rcuwait_wait_event(wait,
>   				(!vcpu->arch.power_off) && (!vcpu->arch.pause),
>   				TASK_INTERRUPTIBLE);
> +			vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
>   
>   			if (vcpu->arch.power_off || vcpu->arch.pause) {
>   				/*

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