Re: [PATCH 09/12] iommu/vt-d: Check device list of domain in domain free path

[Baolu Lu <baolu.lu@linux.intel.com>]

On 2022/6/2 14:29, Tian, Kevin wrote:
>> From: Baolu Lu <baolu.lu@linux.intel.com>
>> Sent: Wednesday, June 1, 2022 7:02 PM
>>
>> On 2022/6/1 17:28, Tian, Kevin wrote:
>>>> From: Lu Baolu <baolu.lu@linux.intel.com>
>>>> Sent: Friday, May 27, 2022 2:30 PM
>>>>
>>>> When the IOMMU domain is about to be freed, it should not be set on
>> any
>>>> device. Instead of silently dealing with some bug cases, it's better to
>>>> trigger a warning to report and fix any potential bugs at the first time.
>>>>
>>>
>>>
>>>>    static void domain_exit(struct dmar_domain *domain)
>>>>    {
>>>> -
>>>> -	/* Remove associated devices and clear attached or cached domains
>>>> */
>>>> -	domain_remove_dev_info(domain);
>>>> +	if (WARN_ON(!list_empty(&domain->devices)))
>>>> +		return;
>>>>
>>>
>>> warning is good but it doesn't mean the driver shouldn't deal with
>>> that situation to make it safer e.g. blocking DMA from all attached
>>> device...
>>
>> I have ever thought the same thing. :-)
>>
>> Blocking DMA from attached device should be done when setting blocking
>> domain to the device. It should not be part of freeing a domain.
> 
> yes but here we are talking about some bug scenario.
> 
>>
>> Here, the caller asks the driver to free the domain, but the driver
>> finds that something is wrong. Therefore, it warns and returns directly.
>> The domain will still be there in use until the next set_domain().
>>
> 
> at least it'd look safer if we always try to unmap the entire domain i.e.:
> 
> static void domain_exit(struct dmar_domain *domain)
> {
> -
> -	/* Remove associated devices and clear attached or cached domains */
> -	domain_remove_dev_info(domain);
> 
> 	if (domain->pgd) {
> 		LIST_HEAD(freelist);
> 
> 		domain_unmap(domain, 0, DOMAIN_MAX_PFN(domain->gaw), &freelist);
> 		put_pages_list(&freelist);
> 	}
> 
> +	if (WARN_ON(!list_empty(&domain->devices)))
> +		return;
> 
> 	kfree(domain);
> }

Fair enough. Removing all mappings is safer.

Best regards,
baolu
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