Re: [PATCH v2 2/2] iommu/tegra241-cmdqv: Fix CMD_SYNC use-after-free on teardown

[Nicolin Chen <nicolinc@nvidia.com>]

On Thu, Jun 11, 2026 at 09:42:05AM +0100, Shameer Kolothum wrote:
> arm_smmu_impl_remove() is registered as a devres action in
> arm_smmu_impl_probe(), before arm_smmu_init_queues() allocates
> smmu->cmdq.q.base. On a devres unwind, whether a failed probe or an
> unbind, the queue is freed first and arm_smmu_impl_remove() then runs
> tegra241_cmdqv_remove_vintf(), whose VINTF deinit issues a CMD_SYNC on
> the freed memory.
> 
> Observed during testing with a QEMU hack that makes the VCMDQ fail to
> enable, so the impl reset fails and probe aborts into the devres unwind:
> 
>  platform NVDA200C:00: tegra241_cmdqv: VINTF0: VCMDQ0/LVCMDQ0: failed to enable, STATUS=0x00000000
>  platform NVDA200C:00: tegra241_cmdqv: VINTF0: VCMDQ0/LVCMDQ0: GERRORN=0x0, GERROR=0x4, CONS=0x0
>  platform NVDA200C:00: tegra241_cmdqv: VINTF0: VCMDQ0/LVCMDQ0: uncleared error detected, resetting
>  arm-smmu-v3 arm-smmu-v3.0.auto: failed to reset impl
>  arm-smmu-v3 arm-smmu-v3.0.auto: probe with driver arm-smmu-v3 failed with error -110
>  Unable to handle kernel paging request at virtual address ffff8000891e0098
>  ...
>  Internal error: Oops: 0000000096000047 [#1] SMP
>  ...
>  Call trace:
>   arm_smmu_cmdq_issue_cmdlist+0x320/0x6fc (P)
>   tegra241_vcmdq_hw_deinit+0x98/0x168
>   tegra241_vintf_hw_deinit+0x5c/0x1b0
>   tegra241_cmdqv_remove_vintf+0x34/0xec
>   tegra241_cmdqv_remove+0x40/0x9c
>   arm_smmu_impl_remove+0x20/0x30
>   devm_action_release+0x14/0x20
>   devres_release_all+0xa8/0x110
>   device_unbind_cleanup+0x18/0x84
>   really_probe+0x1f0/0x29c
> 
> Drop the VINTF deinit from tegra241_cmdqv_remove_vintf() so the unwind no
> longer touches the freed queue. Quiesce the VINTFs earlier instead. Add a
> device_disable() impl op and run it from arm_smmu_disable_action() while
> the CMDQ is still up. That handles a live unbind. A failed reset is already
> handled because tegra241_vintf_hw_init() deinits the VINTF on its own error
> path. tegra241_cmdqv_remove_vintf() is also used by the iommufd viommu
> destroy path, so quiesce there too.
> 
> Fixes: 4dc0d12474f9 ("iommu/tegra241-cmdqv: Add user-space use support")
> Cc: stable@vger.kernel.org
> Signed-off-by: Shameer Kolothum <skolothumtho@nvidia.com>

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