linux-kernel - RE: [PATCH 2/5] iommu: Call helper function to get assigned pasid value

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Date:   Fri, 11 Aug 2023 03:18:40 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
CC:     Baolu Lu <baolu.lu@...ux.intel.com>,
        "Zhang, Tina" <tina.zhang@...el.com>,
        Michael Shavit <mshavit@...gle.com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 2/5] iommu: Call helper function to get assigned pasid
 value

> From: Jason Gunthorpe <jgg@...pe.ca>
> Sent: Friday, August 11, 2023 12:37 AM
> 
> On Thu, Aug 10, 2023 at 07:52:52AM +0000, Tian, Kevin wrote:
> 
> > > The driver should rely on there being exactly one iommu_domain for SVA
> > > per mm so it can hang the mm_notifier off the iommu_domain
> >
> > I'm confused. Isn't this series trying to allow multiple domains per mm?
> 
> It is doing both.
> 
> The main objective is to allow de-duplicating the SVA domains in the
> core code. The driver should be able to assume one SVA domain per
> instance, or even one SVA domain per compatible instance. The driver
> should not do any de-duplication.
> 
> But we can't just store a single iommu_domain in the mm_struct - we
> have the same problem as iommufd and we need to create more domains if
> the domains we already have are incompatible with the device.
> 
> Arguably this should not happen, and in any sane configuration we
> should have only 1 type of IOMMU driver that needs only 1 SVA domain.
> 
> But right now things like SMMUv3 have problems crossing domains across
> instances, so we could have one SVA domain per IOMMU instance until
> that is fixed.
> 

Thanks for the explanation. Tina, please include this information in your
next version so others can easily understand the motivation of introducing
multiple sva domains per mm.