iommu/tegra241-cmdqv: Do not statically map LVCMDQs

To simplify the mappings from global VCMDQs to VINTFs' LVCMDQs, the design
chose to do static allocations and mappings in the global reset function.

However, with the user-owned VINTF support, it exposes a security concern:
if user space VM only wants one LVCMDQ for a VINTF, statically mapping two
or more LVCMDQs creates a hidden VCMDQ that user space could DoS attack by
writing random stuff to overwhelm the kernel with unhandleable IRQs.

Thus, to support the user-owned VINTF feature, a LVCMDQ mapping has to be
done dynamically.

HW allows pre-assigning global VCMDQs in the CMDQ_ALLOC registers, without
finalizing the mappings by keeping CMDQV_CMDQ_ALLOCATED=0. So, add a pair
of map/unmap helper that simply sets/clears that bit.

For kernel-owned VINTF0, move LVCMDQ mappings to tegra241_vintf_hw_init(),
and the unmappings to tegra241_vintf_hw_deinit().

For user-owned VINTFs that will be added, the mappings/unmappings will be
on demand upon an LVCMDQ allocation from the user space.

However, the dynamic LVCMDQ mapping/unmapping can complicate the timing of
calling tegra241_vcmdq_hw_init/deinit(), which write LVCMDQ address space,
i.e. requiring LVCMDQ to be mapped. Highlight that with a note to the top
of either of them.

Link: https://patch.msgid.link/r/be115a8f75537632daf5995b3e583d8a76553fba.1752126748.git.nicolinc@nvidia.com
Acked-by: Pranjal Shrivastava <praan@google.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

0 files changed, 0 insertions, 0 deletions