linux-kernel - RE: [PATCH v7 1/3] iommufd: Add data structure for Intel VT-d stage-1 cache invalidation

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Message-ID: <BN9PR11MB5276EF10FCE9C96F593696E18CBBA@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Tue, 21 Nov 2023 02:54:15 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Jason Gunthorpe <jgg@...dia.com>
CC:     "Liu, Yi L" <yi.l.liu@...el.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
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        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
        "cohuck@...hat.com" <cohuck@...hat.com>,
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        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
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        "Zeng, Xin" <xin.zeng@...el.com>,
        "Zhao, Yan Y" <yan.y.zhao@...el.com>
Subject: RE: [PATCH v7 1/3] iommufd: Add data structure for Intel VT-d stage-1
 cache invalidation

> From: Jason Gunthorpe <jgg@...dia.com>
> Sent: Tuesday, November 21, 2023 7:05 AM
> 
> On Mon, Nov 20, 2023 at 08:26:31AM +0000, Tian, Kevin wrote:
> > > From: Liu, Yi L <yi.l.liu@...el.com>
> > > Sent: Friday, November 17, 2023 9:18 PM
> > >
> > > This adds the data structure for flushing iotlb for the nested domain
> > > allocated with IOMMU_HWPT_DATA_VTD_S1 type.
> > >
> > > This only supports invalidating IOTLB, but no for device-TLB as device-TLB
> > > invalidation will be covered automatically in the IOTLB invalidation if the
> > > underlying IOMMU driver has enabled ATS for the affected device.
> >
> > "no for device-TLB" is misleading. Here just say that cache invalidation
> > request applies to both IOTLB and device TLB (if ATS is enabled ...)
> 
> I think we should forward the ATS invalidation from the guest too?
> That is what ARM and AMD will have to do, can we keep them all
> consistent?
> 
> I understand Intel keeps track of enough stuff to know what the RIDs
> are, but is it necessary to make it different?
> 

probably ask the other way. Now intel-iommu driver always flushes
iotlb and device tlb together then is it necessary to separate them
in uAPI for no good (except doubled syscalls)? :)

anyway this is driver specific contract. I don't see a need to keep
it consistent for all.