linux-kernel - RE: [PATCH 06/17] iommufd/hw_pagetable: Use domain_alloc

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Date:   Fri, 10 Feb 2023 10:50:44 +0000
From:   "Liu, Yi L" <yi.l.liu@...el.com>
To:     Nicolin Chen <nicolinc@...dia.com>,
        Jason Gunthorpe <jgg@...dia.com>
CC:     Matthew Rosato <mjrosato@...ux.ibm.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "cohuck@...hat.com" <cohuck@...hat.com>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "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>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>
Subject: RE: [PATCH 06/17] iommufd/hw_pagetable: Use domain_alloc_user op for
 domain allocation

> From: Nicolin Chen <nicolinc@...dia.com>
> Sent: Friday, February 10, 2023 6:22 AM
> 
> On Thu, Feb 09, 2023 at 04:39:37PM -0400, Jason Gunthorpe wrote:
> > On Thu, Feb 09, 2023 at 11:51:31AM -0800, Nicolin Chen wrote:
> > > On Thu, Feb 09, 2023 at 02:36:49PM -0400, Jason Gunthorpe wrote:
> > > > On Thu, Feb 09, 2023 at 12:59:58PM -0500, Matthew Rosato wrote:
> > > > > really should highlight that).  Otherwise, conditionally calling
> > > > > iommu_domain_alloc(dev->bus) when !ops->domain_alloc_user
> (instead
> > > > > of returning -EOPNOTSUPP) seems to restore the prior functionality
> > > > > for me.
> > > >
> > > > Yes, that is right if the input user data is 0 length or full of 0s
> > > > then we should call the normal driver function
> > >
> > > Maybe I am wrong, yet I recall that doing ops->domain_alloc_user
> > > without a fallback was intentional to rule out drivers that don't
> > > support IOMMUFD?
> >
> > I think we moved away from that to the idea of using the dma_domain
> > patch I suggested..
> >
> > > To be backward-compatible and concern about SMMU, we can opt in
> > > ops->domain_alloc_user upon availability and then add a fallback:
> > >
> > > 	if ((!ops || !ops->domain_alloc_user) && user_data) {
> > > 		rc = -EOPNOTSUPP;
> > > 		goto out_abort;
> > > 	}
> > >
> > > 	if (ops->domain_alloc_user)
> > > 		hwpt->domain = ops->domain_alloc_user(dev, NULL, NULL);
> > > 	else
> > > 		hwpt->domain = iommu_domain_alloc(dev->bus);
> > > 	if (!hwpt->domain) {
> > > 		rc = -ENOMEM;
> > > 		goto out_abort;
> > > 	}
> > >
> > > Yet, even by doing so, this series having the PATCH 07/17 that
> > > moves iopt_table_add_domain() would temporally break IOMMUFD on
> > > ARM platforms, until we add the ops->domain_alloc_user to SMMU
> > > drivers.
> >
> > Drop patch 7 and 8
> >
> > Change patch 12 so it has a unique flow to allocate and IOAS map a
> > HWPT that does not try to share so much code with the existing flow.
> >
> > The HWPT flow should always just call allocate and then map with no
> > effort to attach first. This will fail on ARM SMMU at this point, and
> > that is fine.

Ok. this sounds iopt_table_add_domain() should still be called
right after user hwpt is allocated instead of first device attached.

> >
> > All the existing code should work exactly as it is now and not have
> > any need to be changed.
> >
> > Where things when wrong was trying to share
> > "__iommufd_hw_pagetable_alloc", I think.
> >

Sure. 

> > Don't try to consolidate at this point. Once all the drivers are
> > updated then we could try to consolidate things.
> 
> Yea, I think that's the only way out for now. Though I am not
> sure about other drivers yet, hopefully the SMMU driver(s) is
> the last one that we need to update...

😊 hope it.

Regards,
Yi Liu