linux-kernel - Re: [PATCH v1 0/3] Clean-up arm-smmu-v3-sva.c: remove arm_smmu

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Date:   Tue, 5 Sep 2023 10:32:58 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Michael Shavit <mshavit@...gle.com>
Cc:     iommu@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, will@...nel.org,
        robin.murphy@....com, nicolinc@...dia.com,
        jean-philippe@...aro.org, tina.zhang@...el.com,
        Joerg Roedel <joro@...tes.org>,
        Kevin Tian <kevin.tian@...el.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Mark Brown <broonie@...nel.org>,
        Tomas Krcka <krckatom@...zon.de>,
        Yicong Yang <yangyicong@...ilicon.com>
Subject: Re: [PATCH v1 0/3] Clean-up arm-smmu-v3-sva.c: remove arm_smmu_bond

On Tue, Sep 05, 2023 at 09:24:22PM +0800, Michael Shavit wrote:
> On Tue, Sep 5, 2023 at 8:35 PM Jason Gunthorpe <jgg@...dia.com> wrote:
> >
> > On Tue, Sep 05, 2023 at 07:49:11PM +0800, Michael Shavit wrote:
> > >
> > > Note that arm-smmu-v3-sva performs a second level of normalization by
> > > mapping multiple bonds (now SVA domains) attached to devices with the
> > > same SMMU (if those devices have the same RID domain attached) to a
> > > single arm_smmu_mmu_notifier. This is not affected by these patches.
> >
> > Ultimately the notifier should be per-iommu_domain as well.
> 
> Speaking of, I'm questioning whether the multi-SMMU domain patchseries
> and Tina's sva domain sharing are really prerequisites to get rid of
> the notifier sharing. Is anyone really depending on or taking
> advantage of this?

Currently I don't see any in-tree user of SVA on ARM except for uacce,
which seems to work with only one device (HiSillicon QM).

So, yes, you can probably make it slightly less efficient for a
time. It will be functionally correct still with multiple registered
notifiers.

Jason