Re: [PATCH 3/3] irqchip/gic-v4: Make sure a VPE is locked when VMAPP is issued

[Zhou Wang <wangzhou1@hisilicon.com>]

On 2024/7/19 19:31, Marc Zyngier wrote:
> On Fri, 19 Jul 2024 10:42:02 +0100,
> Zhou Wang <wangzhou1@hisilicon.com> wrote:
>>
>> On 2024/7/5 17:31, Marc Zyngier wrote:
>>> In order to make sure that vpe->col_idx is correctly sampled
>>> when a VMAPP command is issued, we must hold the lock for the
>>> VPE. This is now possible since the introduction of the per-VM
>>> vmapp_lock, which can be taken before vpe_lock in the locking
>>> order.
>>>
>>> Signed-off-by: Marc Zyngier <maz@kernel.org>
>>> ---
>>>  drivers/irqchip/irq-gic-v3-its.c | 8 ++++++--
>>>  1 file changed, 6 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
>>> index b52d60097cad5..951ec140bcea2 100644
>>> --- a/drivers/irqchip/irq-gic-v3-its.c
>>> +++ b/drivers/irqchip/irq-gic-v3-its.c
>>> @@ -1810,7 +1810,9 @@ static void its_map_vm(struct its_node *its, struct its_vm *vm)
>>>  		for (i = 0; i < vm->nr_vpes; i++) {
>>>  			struct its_vpe *vpe = vm->vpes[i];
>>>  
>>> -			its_send_vmapp(its, vpe, true);
>>> +			scoped_guard(raw_spinlock, &vpe->vpe_lock)
>>> +				its_send_vmapp(its, vpe, true);
>>> +
>>>  			its_send_vinvall(its, vpe);
>>>  		}
>>>  	}
>>> @@ -1827,8 +1829,10 @@ static void its_unmap_vm(struct its_node *its, struct its_vm *vm)
>>>  	if (!--vm->vlpi_count[its->list_nr]) {
>>>  		int i;
>>>  
>>> -		for (i = 0; i < vm->nr_vpes; i++)
>>> +		for (i = 0; i < vm->nr_vpes; i++) {
>>> +			guard(raw_spinlock)(&vm->vpes[i]->vpe_lock);
>>>  			its_send_vmapp(its, vm->vpes[i], false);
>>> +		}
>>>  	}
>>>  }
>>>  
>>
>> Hi Marc,
>>
>> It looks like there is ABBA deadlock after applying this series:
>>
>> In its_map_vm: vmapp_lock -> vpe_lock
>> In its_vpe_set_affinity: vpe_to_cpuid_lock(vpe_lock) -> its_send_vmovp(vmapp_lock)
>>
>> Any idea about this?
> 
> Hmmm, well spotted. That's an annoying one.
> 
> Can you give the below hack a go? I've only lightly tested it, as my
> D05 box is on its last leg (it is literally falling apart) and I don't
> have any other GICv4.x box to test on.
> 
> Thanks,
> 
> 	M.
> 
> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
> index 951ec140bcea2..b88c6011c8771 100644
> --- a/drivers/irqchip/irq-gic-v3-its.c
> +++ b/drivers/irqchip/irq-gic-v3-its.c
> @@ -1328,12 +1328,6 @@ static void its_send_vmovp(struct its_vpe *vpe)
>  		return;
>  	}
>  
> -	/*
> -	 * Protect against concurrent updates of the mapping state on
> -	 * individual VMs.
> -	 */
> -	guard(raw_spinlock_irqsave)(&vpe->its_vm->vmapp_lock);
> -
>  	/*
>  	 * Yet another marvel of the architecture. If using the
>  	 * its_list "feature", we need to make sure that all ITSs
> @@ -3808,7 +3802,7 @@ static int its_vpe_set_affinity(struct irq_data *d,
>  	struct its_vpe *vpe = irq_data_get_irq_chip_data(d);
>  	unsigned int from, cpu = nr_cpu_ids;
>  	struct cpumask *table_mask;
> -	unsigned long flags;
> +	unsigned long flags, vmapp_flags;
>  
>  	/*
>  	 * Changing affinity is mega expensive, so let's be as lazy as
> @@ -3822,7 +3816,14 @@ static int its_vpe_set_affinity(struct irq_data *d,
>  	 * protect us, and that we must ensure nobody samples vpe->col_idx
>  	 * during the update, hence the lock below which must also be
>  	 * taken on any vLPI handling path that evaluates vpe->col_idx.
> +	 *
> +	 * Finally, we must protect ourselves against concurrent
> +	 * updates of the mapping state on this VM should the ITS list
> +	 * be in use.
>  	 */
> +	if (its_list_map)
> +		raw_spin_lock_irqsave(&vpe->its_vm->vmapp_lock, vmapp_flags);
> +
>  	from = vpe_to_cpuid_lock(vpe, &flags);
>  	table_mask = gic_data_rdist_cpu(from)->vpe_table_mask;
>  
> @@ -3852,6 +3853,9 @@ static int its_vpe_set_affinity(struct irq_data *d,
>  	irq_data_update_effective_affinity(d, cpumask_of(cpu));
>  	vpe_to_cpuid_unlock(vpe, flags);
>  
> +	if (its_list_map)
> +		raw_spin_unlock_irqrestore(&vpe->its_vm->vmapp_lock, vmapp_flags);
> +
>  	return IRQ_SET_MASK_OK_DONE;
>  }
>

Hi Marc，

We add above code to do test again. Now it is OK.

Bests,
Zhou

>