Re: [PATCH] Revert "iommu/arm-smmu: Convert to domain_alloc_paging()"

From: Jason Gunthorpe <jgg@ziepe.ca>
To: Will Deacon <will@kernel.org>
Cc: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>,
	Robin Murphy <robin.murphy@arm.com>,
	Joerg Roedel <joro@8bytes.org>, Rob Clark <robdclark@gmail.com>,
	linux-arm-kernel@lists.infradead.org, iommu@lists.linux.dev,
	linux-arm-msm@vger.kernel.org
Subject: Re: [PATCH] Revert "iommu/arm-smmu: Convert to domain_alloc_paging()"
Date: Tue, 13 Feb 2024 08:53:03 -0400	[thread overview]
Message-ID: <20240213125303.GJ765010@ziepe.ca> (raw)
In-Reply-To: <20240213121934.GA28726@willie-the-truck>

On Tue, Feb 13, 2024 at 12:19:34PM +0000, Will Deacon wrote:
> > > @@ -875,15 +879,6 @@ static struct iommu_domain *arm_smmu_domain_alloc_paging(struct device *dev)
> > >  	mutex_init(&smmu_domain->init_mutex);
> > >  	spin_lock_init(&smmu_domain->cb_lock);
> > >  
> > > -	if (dev) {
> > > -		struct arm_smmu_master_cfg *cfg = dev_iommu_priv_get(dev);
> > > -
> > > -		if (arm_smmu_init_domain_context(smmu_domain, cfg->smmu, dev)) {
> > > -			kfree(smmu_domain);
> > > -			return NULL;
> > > -		}
> > > -	}
> > > -
> > >  	return &smmu_domain->domain;
> > >  }
> > 
> > Everything else is fine, you already tested with that arrangement.
> 
> Partial reverts are a recipe for confusion, so I'll take this and if you'd
> like to bring back some of the hunks, please can you send a patch on top
> that does that?

The typical kernel standard is to fix bugs in patches and only reach
for a wholesale revert if the community is struggling with bug
fixing. Dmitry already tested removing that hunk, Robin explained the
issue, we understand the bug fix is to remove the
arm_smmu_init_domain_context() call. Nothing justifies a full scale
revert.

I'll send another patch if you want, but it seems like a waste of all
our time.

Jason