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

From: Baolu Lu <baolu.lu@linux.intel.com>
To: "Tian, Kevin" <kevin.tian@intel.com>,
	"iommu@lists.linux.dev" <iommu@lists.linux.dev>
Cc: baolu.lu@linux.intel.com, Joerg Roedel <joro@8bytes.org>,
	Will Deacon <will@kernel.org>,
	Robin Murphy <robin.murphy@arm.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/1] iommu/vt-d: Fix possible recursive locking in intel_iommu_init()
Date: Mon, 25 Jul 2022 17:39:11 +0800	[thread overview]
Message-ID: <c24bd222-9356-0564-414d-d54ca1e2b79b@linux.intel.com> (raw)
In-Reply-To: <BN9PR11MB52765FEEC0ED0EAB5D691FA38C959@BN9PR11MB5276.namprd11.prod.outlook.com>

On 2022/7/25 15:40, Tian, Kevin wrote:
>> From: Baolu Lu <baolu.lu@linux.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@linux.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.

Best regards,
baolu