linux-kernel - Re: [PATCH v2 5/5] vfio/iommu_type1: Simplify group attachment

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Date:   Tue, 21 Jun 2022 14:08:29 -0700
From:   Nicolin Chen <nicolinc@...dia.com>
To:     Robin Murphy <robin.murphy@....com>
CC:     "Tian, Kevin" <kevin.tian@...el.com>,
        "cohuck@...hat.com" <cohuck@...hat.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "jordan@...micpenguin.net" <jordan@...micpenguin.net>,
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        "saiprakash.ranjan@...eaurora.org" <saiprakash.ranjan@...eaurora.org>,
        "zhang.lyra@...il.com" <zhang.lyra@...il.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
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        <linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH v2 5/5] vfio/iommu_type1: Simplify group attachment

On Mon, Jun 20, 2022 at 11:11:01AM +0100, Robin Murphy wrote:
> External email: Use caution opening links or attachments
> 
> 
> On 2022-06-17 03:53, Tian, Kevin wrote:
> > > From: Nicolin Chen <nicolinc@...dia.com>
> > > Sent: Friday, June 17, 2022 6:41 AM
> > > 
> > > > ...
> > > > > -     if (resv_msi) {
> > > > > +     if (resv_msi && !domain->msi_cookie) {
> > > > >                ret = iommu_get_msi_cookie(domain->domain,
> > > > > resv_msi_base);
> > > > >                if (ret && ret != -ENODEV)
> > > > >                        goto out_detach;
> > > > > +             domain->msi_cookie = true;
> > > > >        }
> > > > 
> > > > why not moving to alloc_attach_domain() then no need for the new
> > > > domain field? It's required only when a new domain is allocated.
> > > 
> > > When reusing an existing domain that doesn't have an msi_cookie,
> > > we can do iommu_get_msi_cookie() if resv_msi is found. So it is
> > > not limited to a new domain.
> > 
> > Looks msi_cookie requirement is per platform (currently only
> > for smmu. see arm_smmu_get_resv_regions()). If there is
> > no mixed case then above check is not required.
> > 
> > But let's hear whether Robin has a different thought here.
> 
> Yes, the cookie should logically be tied to the lifetime of the domain
> itself. In the relevant context, "an existing domain that doesn't have
> an msi_cookie" should never exist.

Thanks for the explanation. I will move the iommu_get_msi_cookie()
into alloc_attach_domain(), as Kevin suggested.