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

[Dmitry Baryshkov]

On Tue, 13 Feb 2024 at 14:59, Will Deacon <will at kernel.org> wrote:
>
> On Tue, Feb 13, 2024 at 08:53:03AM -0400, Jason Gunthorpe wrote:
> > 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 can't say I'm aware of any consensus for how to handle this, to be
> completely honest with you. I just personally see a lot of benefit in
> reverting to a known-good state, especially when the revert has been
> posted by the bug reporter. Then we can add stuff on top of that known
> good state without having to worry about any other problems that we're
> yet to uncover. Doesn't really sound controversial...

Well, I'm open to any patch set that ends up fixing the issue. I won't
insist on landing the revert first, it's up to Will and Robin, I'd
say.

If there are any patches for this matter, please Cc me and
linux-arm-msm@, so that we can reply with the Tested-by trailer.

> > I'll send another patch if you want, but it seems like a waste of all
> > our time.
>
> It's a bug fix, of course it's a waste of time! We're talking minutes
> though, right?
>
> Will
-- 
With best wishes
Dmitry