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

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Message-ID: <20220527150108.GS1343366@nvidia.com>
Date:   Fri, 27 May 2022 12:01:08 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     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 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?

Jason