linux-kernel - RE: [PATCH 1/1] iommu/vt-d: Fix possible recursive locking in intel_iommu

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Date:   Thu, 8 Sep 2022 06:31:41 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Baolu Lu <baolu.lu@...ux.intel.com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>
CC:     Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        "Robin Murphy" <robin.murphy@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 1/1] iommu/vt-d: Fix possible recursive locking in
 intel_iommu_init()

> From: Baolu Lu <baolu.lu@...ux.intel.com>
> Sent: Thursday, September 8, 2022 2:13 PM
> 
> 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@...ux.intel.com>
> >>> Sent: Sunday, July 24, 2022 11:00 AM
> >>>
> >>> Hi Kevin,
> >>>
> >>> On 2022/7/21 15:39, Tian, Kevin wrote:
> >>>>> From: Lu Baolu <baolu.lu@...ux.intel.com>
> >>>>> 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@8bytes.org/
> 
> 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?
> 

Yes. With above I'm fine with it given Robin's series has been merged.

Reviewed-by: Kevin Tian <kevin.tian@...el.com>