Re: [PATCH 1/1] iommu/vt-d: Fix possible recursive locking in intel_iommu_init()

[Baolu Lu]

Hi Kevin,

On 2022/7/25 17:39, Baolu Lu wrote:
> On 2022/7/25 15:40, Tian, Kevin wrote:
> > > From: Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx>
> > > Sent: Sunday, July 24, 2022 11:00 AM
> > >
> > > Hi Kevin,
> > >
> > > On 2022/7/21 15:39, Tian, Kevin wrote:
> > > > > From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > > > > Sent: Tuesday, July 19, 2022 7:53 AM
> > > > >
> > > > > @@ -88,7 +89,8 @@ extern struct list_head dmar_drhd_units;
> > > > >    static inline bool dmar_rcu_check(void)
> > > > >    {
> > > > >        return rwsem_is_locked(&dmar_global_lock) ||
> > > > > -           system_state == SYSTEM_BOOTING;
> > > > > +           system_state == SYSTEM_BOOTING ||
> > > > > +           (IS_ENABLED(CONFIG_INTEL_IOMMU)
> > > > > && !intel_iommu_enabled);
> > > > >    }
> > > >
> > > > intel_iommu_enabled is 0 if CONFIG_INTEL_IOMMU is not set.
> > > >
> > > > same for other similar checks.
> > >
> > > Sorry that I didn't get your point. If CONFIG_INTEL_IOMMU is not set,
> > > IS_ENABLED(CONFIG_INTEL_IOMMU) is 0. The adding check has no effect.
> > > Did
> > > I miss anything?
> >
> > My point was that the check on CONFIG_INTEL_IOMMU is unnecessary.
>
> Oh, if INTEL_IOMMU is not configured, the interrupt remapping could also
> be supported, so we still need the rcu protection. We only relax the rcu
> check when INTEL_IOMMU is configured, but not enabled yet.

The next stepping, we will tie INTEL_IOMMU and VT-d IRQ_REMAPPING
together, that will make the VT-d software simpler.

Joerg also proposed this in another discussion thread:

https://lore.kernel.org/all/YrVPelnOi9nql%2F8C@xxxxxxxxxx/

After that, we have no need to add above check anymore. As this is a
quick fix for lockdep splat, we don't need to wait until that done.

Does this work for you?

Best regards,
baolu