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

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Date: Tue, 26 Dec 2023 09:21:49 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: "Liu, Yi L" <yi.l.liu@...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>, "Duan,
 Zhenzhong" <zhenzhong.duan@...el.com>, "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

> From: Liu, Yi L <yi.l.liu@...el.com>
> Sent: Tuesday, December 26, 2023 4:44 PM
> 
> 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.
> 

ok, that makes sense then.