linux-kernel - Re: [RFC 3/8] iommufd: Support attach/replace hwpt per pasid

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Date:   Wed, 27 Sep 2023 10:49:29 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Yi Liu <yi.l.liu@...el.com>, joro@...tes.org,
        alex.williamson@...hat.com, jgg@...dia.com, kevin.tian@...el.com,
        robin.murphy@....com
Cc:     baolu.lu@...ux.intel.com, cohuck@...hat.com, eric.auger@...hat.com,
        nicolinc@...dia.com, kvm@...r.kernel.org, mjrosato@...ux.ibm.com,
        chao.p.peng@...ux.intel.com, yi.y.sun@...ux.intel.com,
        peterx@...hat.com, jasowang@...hat.com,
        shameerali.kolothum.thodi@...wei.com, lulu@...hat.com,
        suravee.suthikulpanit@....com, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        zhenzhong.duan@...el.com, joao.m.martins@...cle.com
Subject: Re: [RFC 3/8] iommufd: Support attach/replace hwpt per pasid

On 9/26/23 5:26 PM, Yi Liu wrote:
> From: Kevin Tian<kevin.tian@...el.com>
> 
> This introduces three APIs for device drivers to manage pasid attach/
> replace/detach.
> 
>      int iommufd_device_pasid_attach(struct iommufd_device *idev,
> 				    u32 pasid, u32 *pt_id);
>      int iommufd_device_pasid_replace(struct iommufd_device *idev,
> 				     u32 pasid, u32 *pt_id);
>      void iommufd_device_pasid_detach(struct iommufd_device *idev,
> 				     u32 pasid);

I am a bit puzzled. Do we really need both attach and replace interfaces
to install a hwpt onto a pasid on device? The IOMMUFD already tracks the
connections between hwpt and {device, pasid}, so it could easily call
the right iommu interfaces (attach vs. replace). Perhaps I overlooked
previous discussion on this.

Best regards,
baolu