linux-kernel - Re: [PATCH 3/7] iommu/vt-d: Use device_block_translation() in dev

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Message-ID: <3dac436c-29e1-de3d-85f3-67e8af608124@linux.intel.com>
Date:   Sat, 5 Nov 2022 10:59:08 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>
Cc:     baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/7] iommu/vt-d: Use device_block_translation() in
 dev_attach error path

On 2022/11/5 10:09, Baolu Lu wrote:
>>
>> btw this change is partial. @attach_dev still calls 
>> iommu_enable_pci_caps()
>> which always tries to enable PCI capabilities w/o checking whether they
>> have been enabled or not. Then user will hit -EBUSY when related PCI
>> helpers are called.
> 
> Good catch!
> 
> How about moving iommu_enable/disable_pci_caps() into
> iommu_probe/release_device() path? I may look into details if there's no
> significant arch gaps.

After reconsideration, it seems that this is not a feasible solution.
This changes the order in which PCI devices enable DMA.In addition, for
the kdump kernel, this is not feasible because there may be on-going DMA
on the device.

Perhaps I can make the iommu_enable_pci_caps() reentrant.

Best regards,
baolu