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

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Message-ID: <15089cab-f896-3c4f-1986-2f84d418696b@linux.intel.com>
Date:   Mon, 18 Apr 2022 19:37:20 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>
Cc:     baolu.lu@...ux.intel.com,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>
Subject: Re: [PATCH 2/3] iommu/vt-d: Drop stop marker messages

On 2022/4/18 14:58, Tian, Kevin wrote:
>> From: Lu Baolu<baolu.lu@...ux.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