linux-kernel - Re: [PATCH v4 08/17] iommufd: Always setup MSI and anforce cc on kernel-managed domains

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Date:   Mon, 23 Oct 2023 11:49:18 -0700
From:   Nicolin Chen <nicolinc@...dia.com>
To:     Jason Gunthorpe <jgg@...dia.com>
CC:     "Tian, Kevin" <kevin.tian@...el.com>,
        "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>,
        "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>,
        "Martins, Joao" <joao.m.martins@...cle.com>
Subject: Re: [PATCH v4 08/17] iommufd: Always setup MSI and anforce cc on
 kernel-managed domains

On Mon, Oct 23, 2023 at 10:59:35AM -0300, Jason Gunthorpe wrote:
> On Sun, Oct 22, 2023 at 05:18:03PM -0700, Nicolin Chen wrote:
> 
> > > > And where should we add this comment? Kdoc of
> > > > the alloc uAPI?
> > > 
> > > Maybe right in front of the only enforce_cc op callback?
> > 
> > OK. How about this? Might be a bit verbose though:
> > 	/*
> > 	 * enforce_cache_coherenc must be determined during the HWPT allocation.
> > 	 * Note that a HWPT (non-CC) created for a device (non-CC) can be later
> > 	 * reused by another device (either non-CC or CC). However, A HWPT (CC)
> > 	 * created for a device (CC) cannot be reused by another device (non-CC)
> > 	 * but only devices (CC). Instead user space in this case would need to
> > 	 * allocate a separate HWPT (non-CC).
> > 	 */
> 
> Ok, fix the spello in enforce_cache_coherenc

Oops.

I also found the existing piece sorta says a similar thing:
         * Set the coherency mode before we do iopt_table_add_domain() as some
         * iommus have a per-PTE bit that controls it and need to decide before
         * doing any maps. 

So, did this and sending v3:
-        * enforce_cache_coherenc must be determined during the HWPT allocation.
+        * The cache coherency mode must be configured here and unchanged later.