Re: [PATCH v2 11/19] iommu/arm-smmu-v3: Do not change the STE twice during arm_smmu_attach_dev()

[Nicolin Chen <nicolinc@nvidia.com>]

On Mon, Nov 13, 2023 at 01:53:18PM -0400, Jason Gunthorpe wrote:
> This was needed because the STE code required the STE to be in
> ABORT/BYPASS inorder to program a cdtable or S2 STE. Now that the STE code
> can automatically handle all transitions we can remove this step
> from the attach_dev flow.
> 
> A few small bugs exist because of this:
> 
> 1) If the core code does BLOCKED -> UNMANAGED with disable_bypass=false
>    then there will be a moment where the STE points at BYPASS. Since
>    this can be done by VFIO/IOMMUFD it is a small security race.
> 
> 2) If the core code does IDENTITY -> DMA then any IOMMU_RESV_DIRECT
>    regions will temporarily become BLOCKED. We'd like drivers to
>    work in a way that allows IOMMU_RESV_DIRECT to be continuously
>    functional during these transitions.
> 
> Make arm_smmu_release_device() put the STE back to the correct
> ABORT/BYPASS setting. Fix a bug where a IOMMU_RESV_DIRECT was ignored on
> this path.
> 
> Notice this subtly depends on the prior arm_smmu_asid_lock change as the
> STE must be put to non-paging before removing the device for the linked
> list to avoid races with arm_smmu_share_asid().
> 
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>