linux-kernel - RE: [PATCH v7 7/9] iommu/vt-d: Allow qi_submit

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Date: Wed, 27 Dec 2023 09:06:19 +0000
From: "Duan, Zhenzhong" <zhenzhong.duan@...el.com>
To: "Liu, Yi L" <yi.l.liu@...el.com>, "Tian, Kevin" <kevin.tian@...el.com>,
	"joro@...tes.org" <joro@...tes.org>, "alex.williamson@...hat.com"
	<alex.williamson@...hat.com>, "jgg@...dia.com" <jgg@...dia.com>,
	"robin.murphy@....com" <robin.murphy@....com>, "baolu.lu@...ux.intel.com"
	<baolu.lu@...ux.intel.com>
CC: "cohuck@...hat.com" <cohuck@...hat.com>, "eric.auger@...hat.com"
	<eric.auger@...hat.com>, "nicolinc@...dia.com" <nicolinc@...dia.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>, "mjrosato@...ux.ibm.com"
	<mjrosato@...ux.ibm.com>, "chao.p.peng@...ux.intel.com"
	<chao.p.peng@...ux.intel.com>, "yi.y.sun@...ux.intel.com"
	<yi.y.sun@...ux.intel.com>, "peterx@...hat.com" <peterx@...hat.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	"shameerali.kolothum.thodi@...wei.com"
	<shameerali.kolothum.thodi@...wei.com>, "lulu@...hat.com" <lulu@...hat.com>,
	"suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
	"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
	"joao.m.martins@...cle.com" <joao.m.martins@...cle.com>, "Zeng, Xin"
	<xin.zeng@...el.com>, "Zhao, Yan Y" <yan.y.zhao@...el.com>,
	"j.granados@...sung.com" <j.granados@...sung.com>
Subject: RE: [PATCH v7 7/9] iommu/vt-d: Allow qi_submit_sync() to return the
 QI faults



>-----Original Message-----
>From: Liu, Yi L <yi.l.liu@...el.com>
>Sent: Tuesday, December 26, 2023 4:44 PM
>Subject: Re: [PATCH v7 7/9] iommu/vt-d: Allow qi_submit_sync() to return
>the QI faults
>
>On 2023/12/26 14:15, Yi Liu wrote:
>>
>>
>> On 2023/12/26 12:13, Tian, Kevin wrote:
>>>> From: Liu, Yi L <yi.l.liu@...el.com>
>>>> Sent: Tuesday, December 26, 2023 12:03 PM
>>>>
>>>> On 2023/12/22 12:23, Tian, Kevin wrote:
>>>>>> From: Liu, Yi L <yi.l.liu@...el.com>
>>>>>> Sent: Thursday, December 21, 2023 11:40 PM
>>>>>>
>>>>>> +    fault &= DMA_FSTS_IQE | DMA_FSTS_ITE | DMA_FSTS_ICE;
>>>>>> +    if (fault) {
>>>>>> +        if (fsts)
>>>>>> +            *fsts |= fault;
>>>>>
>>>>> do we expect the fault to be accumulated? otherwise it's clearer to
>>>>> just do direct assignment instead of asking for the caller to clear
>>>>> the variable before invocation.
>>>>
>>>> not quite get. do you mean the fault should not be cleared in the caller
>>>> side?
>>>>
>>>
>>> I meant:
>>>
>>>     if (fsts)
>>>         *fsts = fault;
>>>
>>> unless there is a reason to *OR* the original value.
>>
>> I guess no such a reason. :) let me modify it.
>
>hmmm, replied too soon. The qi_check_fault() would be called multiple
>times in one invalidation circle as qi_submit_sync() needs to see if any
>fault happened before the hw writes back QI_DONE to the wait descriptor.
>There can be ICE which may eventually result in ITE. So caller of
>qi_check_fault()
>would continue to wait for QI_DONE. So qi_check_fault() returns 0 to let
>qi_submit_sync() go on though ICE detected. If we use '*fsts = fault;',
>then ICE would be missed since the input fsts pointer is the same in
>one qi_submit_sync() call.

Is it necessary to return fault to user if qi_check_fault() return -EAGAIN and
a restart run succeeds?

Thanks
Zhenzhong