linux-kernel - Re: [PATCH v3 4/7] iommu/vt-d: Fold dmar_remove_one_dev

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Date:   Wed, 16 Nov 2022 16:02:46 +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 v3 4/7] iommu/vt-d: Fold dmar_remove_one_dev_info() into
 its caller

On 2022/11/16 13:35, Tian, Kevin wrote:
>> From: Baolu Lu<baolu.lu@...ux.intel.com>
>> Sent: Wednesday, November 16, 2022 12:36 PM
>>
>> On 11/16/22 11:53 AM, Tian, Kevin wrote:
>>>> From: Lu Baolu<baolu.lu@...ux.intel.com>
>>>> Sent: Monday, November 14, 2022 9:41 AM
>>>> @@ -4562,7 +4538,10 @@ static void intel_iommu_release_device(struct
>>>> device *dev)
>>>>    {
>>>>    	struct device_domain_info *info = dev_iommu_priv_get(dev);
>>>>
>>>> -	dmar_remove_one_dev_info(dev);
>>>> +	iommu_disable_pci_caps(info);
>>>> +	domain_context_clear(info);
>>>> +	device_block_translation(dev);
>>> clear context after blocking translation.
>> Unfortunately domain_context_clear() needs reference to info->domain
>> (for domain id when flushing cache), which is cleared in
>> device_block_translation().
>>
> this sounds an ordering problem. clearing context should be after
> blocking translation in concept.

At present, when the default domain is attached to the device, we first
populate the pasid table entry, and then populate the device context
entry. Above code is just the reverse operation.

Can you see any practical problems caused by this sequence? If so, it
seems that we should carefully consider whether such problems already
exist.

Best regards,
baolu