Re: [PATCH v2 12/19] iommu/arm-smmu-v3: Put writing the context descriptor in the right order

[Jason Gunthorpe <jgg@nvidia.com>]

On Wed, Nov 15, 2023 at 11:32:28PM +0800, Michael Shavit wrote:

> > Lift this code out of arm_smmu_detach_dev() so it can all be sequenced
> > properly. The only other caller is arm_smmu_release_device() and it is
> > going to free the cdtable anyhow, so it doesn't matter what is in it.
> >
> > Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> Reviewed-by: Michael Shavit <mshavit@google.com>
> 
> This patch might be a better fit before the previous one. When going
> from S1 to S2 or bypass:
> Pre-both patches, attach_dev() installs a NULL STE, then clears the
> now unused CDE, then installs a new STE.
> After the previous patch, attach_dev() clears the *still used* CDE,
> and then replaces the STE.
> After this patch, attach_dev() replaces the STE, and then clears the CDE
> 
> Reordering the two patches removes the scenario where we could hit a
> NULL-ed CDE.

NULLed = non-valid

I see what you mean, but I haven't thought carefully about a different
order so I'd rather leave it..

Regardless of order the two prior patches will have cases that hit
non-valid/abort STE/CDEs, each step removes a few cases.

Thanks,
Jason