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

[Marc Zyngier]

On Fri, 19 Jul 2024 10:42:02 +0100,
Zhou Wang <wangzhou1@xxxxxxxxxxxxx> 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@xxxxxxxxxx>
> > ---
> >  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;
 }
 

-- 
Without deviation from the norm, progress is not possible.