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

Baolu Lu
2022-06-06T01:35:46Z

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