The idea behind this patch is to delay the freeing of PT entry objects
until the TLB flush is done.

This patch:
- Adds a tlb_flush_waitlist in amdgpu_vm_update_params which will keep the
  objects that need to be freed after tlb_flush.
- Adds PT entries in this list in amdgpu_vm_ptes_update after finding
  the PT entry.
- Changes functionality of amdgpu_vm_pt_free_dfs from (df_search + free)
  to simply freeing of the BOs, also renames it to
  amdgpu_vm_pt_free_list to reflect this same.
- Exports function amdgpu_vm_pt_free_list to be called directly.
- Calls amdgpu_vm_pt_free_list directly from amdgpu_vm_update_range.

V2: rebase
V4: Addressed review comments from Christian
    - add only locked PTEs entries in TLB flush waitlist.
    - do not create a separate function for list flush.
    - do not create a new lock for TLB flush.
    - there is no need to wait on tlb_flush_fence exclusively.

V5: Addressed review comments from Christian
    - change the amdgpu_vm_pt_free_dfs's functionality to simple freeing
      of the objects and rename it.
    - add all the PTE objects in params->tlb_flush_waitlist
    - let amdgpu_vm_pt_free_root handle the freeing of BOs independently
    - call amdgpu_vm_pt_free_list directly

V6: Rebase
V7: Rebase
V8: Added a NULL check to fix this backtrace issue:
[  415.351447] BUG: kernel NULL pointer dereference, address: 0000000000000008
[  415.359245] #PF: supervisor write access in kernel mode
[  415.365081] #PF: error_code(0x0002) - not-present page
[  415.370817] PGD 101259067 P4D 101259067 PUD 10125a067 PMD 0
[  415.377140] Oops: 0002 [#1] PREEMPT SMP NOPTI
[  415.382004] CPU: 0 PID: 25481 Comm: test_with_MPI.e Tainted: G           OE     5.18.2-mi300-build-140423-ubuntu-22.04+ #24
[  415.394437] Hardware name: AMD Corporation Sh51p/Sh51p, BIOS RMO1001AS 02/21/2024
[  415.402797] RIP: 0010:amdgpu_vm_ptes_update+0x6fd/0xa10 [amdgpu]
[  415.409648] Code: 4c 89 ff 4d 8d 66 30 e8 f1 ed ff ff 48 85 db 74 42 48 39 5d a0 74 40 48 8b 53 20 48 8b 4b 18 48 8d 43 18 48 8d 75 b0 4c 89 ff <48
> 89 51 08 48 89 0a 49 8b 56 30 48 89 42 08 48 89 53 18 4c 89 63
[  415.430621] RSP: 0018:ffffc9000401f990 EFLAGS: 00010287
[  415.436456] RAX: ffff888147bb82f0 RBX: ffff888147bb82d8 RCX: 0000000000000000
[  415.444426] RDX: 0000000000000000 RSI: ffffc9000401fa30 RDI: ffff888161f80000
[  415.452397] RBP: ffffc9000401fa80 R08: 0000000000000000 R09: ffffc9000401fa00
[  415.460368] R10: 00000007f0cc0000 R11: 00000007f0c85000 R12: ffffc9000401fb20
[  415.468340] R13: 00000007f0d00000 R14: ffffc9000401faf0 R15: ffff888161f80000
[  415.476312] FS:  00007f132ff89840(0000) GS:ffff889f87c00000(0000) knlGS:0000000000000000
[  415.485350] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  415.491767] CR2: 0000000000000008 CR3: 0000000161d46003 CR4: 0000000000770ef0
[  415.499738] PKRU: 55555554
[  415.502750] Call Trace:
[  415.505482]  <TASK>
[  415.507825]  amdgpu_vm_update_range+0x32a/0x880 [amdgpu]
[  415.513869]  amdgpu_vm_clear_freed+0x117/0x250 [amdgpu]
[  415.519814]  amdgpu_amdkfd_gpuvm_unmap_memory_from_gpu+0x18c/0x250 [amdgpu]
[  415.527729]  kfd_ioctl_unmap_memory_from_gpu+0xed/0x340 [amdgpu]
[  415.534551]  kfd_ioctl+0x3b6/0x510 [amdgpu]

V9: Addressed review comments from Christian
    - No NULL check reqd for root PT freeing
    - Free PT list regardless of needs_flush
    - Move adding BOs in list in a separate function

V10: Added Christian's RB
V11: squash in list fix

Cc: Christian König <Christian.Koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Felix Kuehling <felix.kuehling@amd.com>
Cc: Rajneesh Bhardwaj <rajneesh.bhardwaj@amd.com>
Acked-by: Felix Kuehling <felix.kuehling@amd.com>
Acked-by: Rajneesh Bhardwaj <rajneesh.bhardwaj@amd.com>
Reviewed-by: Christian König <Christian.Koenig@amd.com>
Tested-by: Rajneesh Bhardwaj <rajneesh.bhardwaj@amd.com>
Signed-off-by: Shashank Sharma <shashank.sharma@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>