linux-kernel - Re: [PATCH 03/12] iommu/vt-d: Remove clearing translation data in disable_dmar

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Message-ID: <a1e27717-3761-a521-79fa-6f74b6f88ffd@linux.intel.com>
Date:   Sun, 29 May 2022 13:22:47 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Liu Yi L <yi.l.liu@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 03/12] iommu/vt-d: Remove clearing translation data in
 disable_dmar_iommu()

On 2022/5/27 23:01, Jason Gunthorpe wrote:
> On Fri, May 27, 2022 at 02:30:10PM +0800, Lu Baolu wrote:
>> The disable_dmar_iommu() is called when IOMMU initialzation fails or
>> the IOMMU is hot-removed from the system. In both cases, there is no
>> need to clear the IOMMU translation data structures for devices.
>>
>> On the initialization path, the device probing only happens after the
>> IOMMU is initialized successfully, hence there're no translation data
>> structures.
>>
>> On the hot-remove path, there is no real use case where the IOMMU is
>> hot-removed, but the devices that it manages are still alive in the
>> system. The translation data structures were torn down during device
>> release, hence there's no need to repeat it in IOMMU hot-remove path
>> either.
> 
> Can you leave behind a 1 statement WARN_ON of some kind to check this?

Sure. As the default domain is the first domain allocated for a device
and the last one freed. We can WARN_ON the case where there's still
domain IDs in use. How do you like this?

+       /*
+        * All iommu domains must have been detached from the devices,
+        * hence there should be no domain IDs in use.
+        */
+       if (WARN_ON(bitmap_weight(iommu->domain_ids, cap_ndoms(iommu->cap))
+                   != NUM_RESERVED_DID))
+               return;

Best regards,
baolu