linux-kernel - Re: [PATCH v1 7/7] iommu/arm-smmu-v3: Move CD table to arm_smmu

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Date:   Fri, 28 Jul 2023 15:52:55 +0800
From:   Michael Shavit <mshavit@...gle.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>, jean-philippe@...aro.org,
        nicolinc@...dia.com, baolu.lu@...ux.intel.com,
        linux-arm-kernel@...ts.infradead.org, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 7/7] iommu/arm-smmu-v3: Move CD table to arm_smmu_master

On Fri, Jul 28, 2023 at 2:43 AM Jason Gunthorpe <jgg@...dia.com> wrote:
>
> On Fri, Jul 28, 2023 at 02:26:23AM +0800, Michael Shavit wrote:
> > Each master is now allocated a CD table at probe time,
>
> Currently it is allocated during arm_smmu_domain_finalise_s1(), so it
> isn't allocated at probe time.

Urh right, I meant that this patch moves the allocation to the probe,
but that was misleading wording for sure.

> I think the right place to put the allocation is during the attach op,
> the first time we need a CD table then go and allocate it. If we can't
> then domain attach fails with -ENOMEM.
>
> Then you can put the free in a detach op once the CD table becomes
> empty and it behaves much like it already does.

Hmmm fair. I can't think of a reason that the table *must* be
pre-allocated for the PASID feature, and that could always be a
different commit if it turns out to be necessary.