linux-kernel - Re: [PATCH v5 6/9] iommu/arm-smmu-v3: Move CD table to arm_smmu

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Date:   Thu, 10 Aug 2023 15:38:29 +0100
From:   Will Deacon <will@...nel.org>
To:     Michael Shavit <mshavit@...gle.com>
Cc:     iommu@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, robin.murphy@....com,
        nicolinc@...dia.com, jgg@...dia.com, jean-philippe@...aro.org
Subject: Re: [PATCH v5 6/9] iommu/arm-smmu-v3: Move CD table to
 arm_smmu_master

On Thu, Aug 10, 2023 at 05:23:37PM +0800, Michael Shavit wrote:
> >
> > > @@ -2465,6 +2450,22 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
> > >       if (smmu_domain->stage != ARM_SMMU_DOMAIN_BYPASS)
> > >               master->ats_enabled = arm_smmu_ats_supported(master);
> > >
> > > +     if (smmu_domain->stage == ARM_SMMU_DOMAIN_S1) {
> > > +             if (!master->cd_table.cdtab) {
> > > +                     ret = arm_smmu_alloc_cd_tables(master);
> > > +                     if (ret) {
> > > +                             master->domain = NULL;
> > > +                             return ret;
> > > +                     }
> > > +             }
> > > +
> > > +             ret = arm_smmu_write_ctx_desc(master, 0, &smmu_domain->cd);
> > > +             if (ret) {
> > > +                     master->domain = NULL;
> > > +                     return ret;
> >
> > Can you leak the cd tables here if you just allocated them?
> 
> The CD table is only de-allocated when the SMMU device is released, so
> this isn't "leaked" anymore than on a successful attachment. In a
> previous version of this patch, this CD table was even pre-allocated
> at probe time but is deferred to first attach following this
> discussion: https://lore.kernel.org/lkml/ZMOzs1%2FxoEPX2+vA@nvidia.com/

Thanks, that makes sense.

> > > @@ -2472,10 +2473,7 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
> > >       spin_unlock_irqrestore(&smmu_domain->devices_lock, flags);
> > >
> > >       arm_smmu_enable_ats(master);
> > > -
> > > -out_unlock:
> > > -     mutex_unlock(&smmu_domain->init_mutex);
> > > -     return ret;
> > > +     return 0;
> > >  }
> > >
> > >  static int arm_smmu_map_pages(struct iommu_domain *domain, unsigned long iova,
> > > @@ -2719,6 +2717,8 @@ static void arm_smmu_release_device(struct device *dev)
> > >       arm_smmu_detach_dev(master);
> > >       arm_smmu_disable_pasid(master);
> > >       arm_smmu_remove_master(master);
> > > +     if (master->cd_table.cdtab_dma)
> >
> > Why are you checking 'cdtab_dma' here instead of just 'cdtab'?
> 
> cd_table is statically allocated as part of the arm_smmu_master
> struct. I suppose it could be allocated by arm_smmu_alloc_cd_tables()
> instead?

I just mean you could check 'master->cd_table.cdtab' like you do in other
places. The DMA pointer is supposed to be opaque.

Will