linux-kernel - Re: [PATCH v6 2/6] iommufd: Add IOMMU_HWPT

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Message-ID: <20231213141138.GX3014157@nvidia.com>
Date:   Wed, 13 Dec 2023 10:11:38 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Liu, Yi L" <yi.l.liu@...el.com>
Cc:     "Tian, Kevin" <kevin.tian@...el.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
        "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>,
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        "yi.y.sun@...ux.intel.com" <yi.y.sun@...ux.intel.com>,
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        "jasowang@...hat.com" <jasowang@...hat.com>,
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        <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>,
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        "joao.m.martins@...cle.com" <joao.m.martins@...cle.com>,
        "Zeng, Xin" <xin.zeng@...el.com>,
        "Zhao, Yan Y" <yan.y.zhao@...el.com>
Subject: Re: [PATCH v6 2/6] iommufd: Add IOMMU_HWPT_INVALIDATE

On Wed, Dec 13, 2023 at 01:47:54PM +0000, Liu, Yi L wrote:
> > From: Jason Gunthorpe <jgg@...dia.com>
> > Sent: Tuesday, December 12, 2023 10:40 PM
> > 
> > On Tue, Dec 12, 2023 at 01:45:16PM +0000, Liu, Yi L wrote:
> > > > From: Jason Gunthorpe <jgg@...dia.com>
> > > > Sent: Monday, December 11, 2023 9:22 PM
> > > >
> > > > On Mon, Dec 11, 2023 at 03:53:40PM +0800, Yi Liu wrote:
> > > >
> > > > > > >  From that thread Jason mentioned to make the invalidation format
> > > > > > > part of domain allocation. If that is the direction to go then there
> > > > > > > won't be multiple invalidation formats per hwpt. The user should
> > > > > > > create multiple hwpt's per invalidation format (though mixing
> > > > > > > formats in one virtual platform is very unlikely)?
> > > > > >
> > > > > > I think we could do either, but I have a vauge cleanness preference
> > > > > > that the enums are just different? That would follow a pretty typical
> > > > > > pattern for a structure tag to reflect the content of the structure.
> > > > >
> > > > > Is this still following the direction to make the invalidation format
> > > > > part of domain allocation?
> > > >
> > > > I think you should make it seperate
> > >
> > > Sure. I'll add a separate enum for cache invalidation format. Just to
> > > see if it is good to pass down the invalidation format in the hwpt
> > > alloc path? So iommu driver can check if the invalidation format
> > > can be used for the hwpt to be allocated.
> > 
> > I would skip it in the invalidation. If necessary drivers can push a 0
> > length invalidation to do 'try and fail' discovery of supported types.
> 
> I think you mean keep passing the req_type in cache invalidation path
> instead of the way I proposed. For the 'try and fail' discovery, we should
> allow a zero-length array, is it? If the req_type is supported by the iommu
> driver, then return successful, otherwise fail the ioctl. Is it?

Yes

Jason