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 09:25:23 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Michael Shavit <mshavit@...gle.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 07:11:46PM +0800, Michael Shavit wrote:
> On Fri, Jul 28, 2023 at 2:43 AM Jason Gunthorpe <jgg@...dia.com> wrote:
> 
> > Then you can put the free in a detach op once the CD table becomes
> > empty and it behaves much like it already does.
> 
> This turns out to be a bit tricky; the SMMU driver detaches the
> currently attached domain whenever a new domain is attached with
> attach_dev().

Oh, yeah, it is a bit quirky that way

> More generally, do we really want to be de-allocating
> the table whenever we switch between an S1 domain and other domain
> types that don't make use of the table (such as IDENTITY or NESTED)?

Probably.

> One solution is to defer the allocation to the first attach_op, but
> only free when the master is freed (this patch's v1 behavior).

That seems reasonable, just don't allocate it at probe time since
PASID is very rarely used.

Jason