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

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Date:   Thu, 7 Dec 2023 10:42:08 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     "Liu, Yi L" <yi.l.liu@...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>,
        "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>
Subject: Re: [PATCH v6 2/6] iommufd: Add IOMMU_HWPT_INVALIDATE

On Thu, Dec 07, 2023 at 09:04:00AM +0000, Tian, Kevin wrote:
> > From: Liu, Yi L <yi.l.liu@...el.com>
> > Sent: Thursday, December 7, 2023 2:59 PM
> > 
> > On 2023/11/17 21:07, Yi Liu wrote:
> > > @@ -613,4 +614,38 @@ struct iommu_hwpt_get_dirty_bitmap {
> > >   #define IOMMU_HWPT_GET_DIRTY_BITMAP _IO(IOMMUFD_TYPE, \
> > >
> > 	IOMMUFD_CMD_HWPT_GET_DIRTY_BITMAP)
> > >
> > > +/**
> > > + * struct iommu_hwpt_invalidate - ioctl(IOMMU_HWPT_INVALIDATE)
> > > + * @size: sizeof(struct iommu_hwpt_invalidate)
> > > + * @hwpt_id: HWPT ID of a nested HWPT for cache invalidation
> > > + * @reqs_uptr: User pointer to an array having @req_num of cache
> > invalidation
> > > + *             requests. The request entries in the array are of fixed width
> > > + *             @req_len, and contain a user data structure for invalidation
> > > + *             request specific to the given hardware page table.
> > > + * @req_type: One of enum iommu_hwpt_data_type, defining the data
> > type of all
> > > + *            the entries in the invalidation request array. It should suit
> > > + *            with the data_type passed per the allocation of the hwpt pointed
> > > + *            by @hwpt_id.
> > 
> > @Jason and Kevin,
> > 
> > Here a check with you two. I had a conversation with Nic on the definition
> > of req_type here. It was added to support potential multiple kinds of cache
> > invalidation data types for a invalidating cache for a single hwpt type[1].
> > But we defined it as reusing the hwpt_data_type. In this way, it is not
> > able to support the potential case in[1]. is it? Shall we define a separate
> > enum for invalidation data types? And how can we let user know the
> > available invalidation data types for a hwpt type? Any idea?
> > 
> > [1] https://lore.kernel.org/linux-
> > iommu/20231018163720.GA3952@...dia.com/
> > 
> 
> 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.

Jason