linux-kernel - Re: [RFC PATCH v1 3/8] iommu/arm-smmu-v3-sva: Allocate new ASID from installed

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Date:   Tue, 22 Aug 2023 16:53:33 +0800
From:   Michael Shavit <mshavit@...gle.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     iommu@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, will@...nel.org, nicolinc@...dia.com,
        tina.zhang@...el.com, jean-philippe@...aro.org,
        robin.murphy@....com
Subject: Re: [RFC PATCH v1 3/8] iommu/arm-smmu-v3-sva: Allocate new ASID from installed_smmus

On Mon, Aug 21, 2023 at 10:56 PM Jason Gunthorpe <jgg@...dia.com> wrote:
>
> On Mon, Aug 21, 2023 at 10:39:14PM +0800, Michael Shavit wrote:
> > > > > > (on a loop over every smmu the domain in arm_smmu_mmu_notifier_get is
> > > > > > attached to, which just at a glance looks headache inducing because of
> > > > > > sva's piggybacking on the rid domain.)
> > > > >
> > > > > Not every smmu, just the one you are *currently* attaching to. We
> > > > > don't care if the *other* smmu's have different ASIDs, maybe they are
> > > > > not using BTM, or won't use SVA.
> > > >
> > > > I mean because the domain in arm_smmu_mmu_notifier_get is the RID
> > > > domain (not the SVA domain, same issue we discussed in previous
> > > > thread) , which can be attached to multiple SMMUs.
> > >
> > > Oh that is totally nonsensical. I expect you will need to fix that
> > > sooner than later. Once the CD table is moved and there is a proper
> > > way to track the PASID it should not be needed. It shouldn't fall into
> > > the decision making about where to put the ASID xarray.
> >
> > Right I got a bit of a chicken and egg problem with all these series.
>
> Yes, I'm not surprised to hear this
>
> Still, it would nice to move forward without going in a weird
> direction too much.
>
> Once the CD table is moved to the master what do you think is blocking
> fixing up the SVA stuff to not rely on a RID domain?

These aren't necessarily strict dependencies, but ideally I'd like to:
1. Natively support PASID attachments in the smmu domain (patch(es)
from the set_dev_pasid series)
2. Support attaching a domain to multiple SMMUs (this series)
3. SVA framework support for allocating a single SVA domain per MM
struct (Tina's series)

SVA can then directly attach an sva domain to a master in its
set_dev_pasid call, without having to do any sort of sharing of
smmu_notifiers or CDs across domains. The SVA domain allocated would
directly be attached to the master.