Re: [PATCH 2/3] iommu/vt-d: Drop stop marker messages

Lu Baolu
2022-04-18T11:37:34Z

On 2022/4/18 14:58, Tian, Kevin wrote:
>> From: Lu Baolu<baolu.lu@linux.intel.com>
>> Sent: Saturday, April 16, 2022 8:31 PM
>>
>> The VT-d driver explicitly drains the pending page requests when a CPU
>> page table (represented by a mm struct) is unbound from a PASID according
>> to the procedures defined in the VT-d spec. Hence, there's no need to
>> report the stop-marker message in prq_event_thread(). The stop marker
>> messages do not need a response. This drops stop marker messages silently
>> if any of them is found in the page request queue.
> The comment for iommu_queue_iopf says:
>
> * This module doesn't handle PCI PASID Stop Marker; IOMMU drivers must discard
> * them before reporting faults. A PASID Stop Marker (LRW = 0b100) doesn't
> * expect a response. It may be generated when disabling a PASID (issuing a
> * PASID stop request) by some PCI devices.
>
> So obviously the current vt-d driver behavior violates that requirement.
> Then should this be a bug fix instead?
>

Our platforms have no devices issuing Stop Marker messages yet. But in a
virtualization environment, a device might be emulated with this
capability. Yes! Let me make it as a fix.

Best regards,
baolu