Re: [PATCH v8] drm/amdgpu: sync page table freeing with tlb flush

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On 18/03/2024 16:01, Christian König wrote:
Am 18.03.24 um 15:44 schrieb Shashank Sharma:
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]

Cc: Christian König <Christian.Koenig@xxxxxxx>
Cc: Alex Deucher <alexander.deucher@xxxxxxx>
Cc: Felix Kuehling <felix.kuehling@xxxxxxx>
Cc: Rajneesh Bhardwaj <rajneesh.bhardwaj@xxxxxxx>
Acked-by: Felix Kuehling <felix.kuehling@xxxxxxx>
Acked-by: Rajneesh Bhardwaj <rajneesh.bhardwaj@xxxxxxx>
Tested-by: Rajneesh Bhardwaj <rajneesh.bhardwaj@xxxxxxx>
Signed-off-by: Shashank Sharma <shashank.sharma@xxxxxxx>
---
  drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c    |  5 +-
  drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h    |  7 +++
  drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c | 58 +++++++++++++----------
  3 files changed, 45 insertions(+), 25 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
index 26f1c3359642..eaa402f99fe0 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
@@ -977,6 +977,7 @@ int amdgpu_vm_update_range(struct amdgpu_device *adev, struct amdgpu_vm *vm,
      params.unlocked = unlocked;
      params.needs_flush = flush_tlb;
      params.allow_override = allow_override;
+    INIT_LIST_HEAD(&params.tlb_flush_waitlist);
        /* Implicitly sync to command submissions in the same VM before
       * unmapping. Sync to moving fences before mapping.
@@ -1062,8 +1063,10 @@ int amdgpu_vm_update_range(struct amdgpu_device *adev, struct amdgpu_vm *vm,
      if (r)
          goto error_unlock;
  -    if (params.needs_flush)
+    if (params.needs_flush) {
          r = amdgpu_vm_tlb_flush(&params, fence);
+        amdgpu_vm_pt_free_list(adev, &params);

This is completed independent of the VM flush and should always be called.

+    }
    error_unlock:
      amdgpu_vm_eviction_unlock(vm);
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
index b0a4fe683352..54d7da396de0 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
@@ -266,6 +266,11 @@ struct amdgpu_vm_update_params {
       * to be overridden for NUMA local memory.
       */
      bool allow_override;
+
+    /**
+     * @tlb_flush_waitlist: temporary storage for BOs until tlb_flush
+     */
+    struct list_head tlb_flush_waitlist;
  };
    struct amdgpu_vm_update_funcs {
@@ -547,6 +552,8 @@ int amdgpu_vm_ptes_update(struct amdgpu_vm_update_params *params,
                uint64_t start, uint64_t end,
                uint64_t dst, uint64_t flags);
  void amdgpu_vm_pt_free_work(struct work_struct *work);
+void amdgpu_vm_pt_free_list(struct amdgpu_device *adev,
+                struct amdgpu_vm_update_params *params);
    #if defined(CONFIG_DEBUG_FS)
  void amdgpu_debugfs_vm_bo_info(struct amdgpu_vm *vm, struct seq_file *m); diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
index 601df0ce8290..9231edfb427e 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
@@ -622,40 +622,30 @@ void amdgpu_vm_pt_free_work(struct work_struct *work)
  }
    /**
- * amdgpu_vm_pt_free_dfs - free PD/PT levels
+ * amdgpu_vm_pt_free_list - free PD/PT levels
   *
   * @adev: amdgpu device structure
- * @vm: amdgpu vm structure
- * @start: optional cursor where to start freeing PDs/PTs
- * @unlocked: vm resv unlock status
+ * @params: see amdgpu_vm_update_params definition
   *
- * Free the page directory or page table level and all sub levels.
+ * Free the page directory objects saved in the flush list
   */
-static void amdgpu_vm_pt_free_dfs(struct amdgpu_device *adev,
-                  struct amdgpu_vm *vm,
-                  struct amdgpu_vm_pt_cursor *start,
-                  bool unlocked)
+void amdgpu_vm_pt_free_list(struct amdgpu_device *adev,
+                struct amdgpu_vm_update_params *params)
  {
-    struct amdgpu_vm_pt_cursor cursor;
-    struct amdgpu_vm_bo_base *entry;
+    struct amdgpu_vm_bo_base *entry, *next;
+    struct amdgpu_vm *vm = params->vm;
+    bool unlocked = params->unlocked;
        if (unlocked) {
          spin_lock(&vm->status_lock);
-        for_each_amdgpu_vm_pt_dfs_safe(adev, vm, start, cursor, entry)
-            list_move(&entry->vm_status, &vm->pt_freed);
-
-        if (start)
-            list_move(&start->entry->vm_status, &vm->pt_freed);
+        list_splice_init(&vm->pt_freed, &params->tlb_flush_waitlist);
          spin_unlock(&vm->status_lock);
          schedule_work(&vm->pt_free_work);
          return;
      }
  -    for_each_amdgpu_vm_pt_dfs_safe(adev, vm, start, cursor, entry)
+    list_for_each_entry_safe(entry, next, &params->tlb_flush_waitlist, vm_status)
          amdgpu_vm_pt_free(entry);
-
-    if (start)
-        amdgpu_vm_pt_free(start->entry);
  }
    /**
@@ -667,7 +657,13 @@ static void amdgpu_vm_pt_free_dfs(struct amdgpu_device *adev,
   */
  void amdgpu_vm_pt_free_root(struct amdgpu_device *adev, struct amdgpu_vm *vm)
  {
-    amdgpu_vm_pt_free_dfs(adev, vm, NULL, false);
+    struct amdgpu_vm_pt_cursor cursor;
+    struct amdgpu_vm_bo_base *entry;
+
+    for_each_amdgpu_vm_pt_dfs_safe(adev, vm, NULL, cursor, entry) {
+        if (entry)

Entry can't be NULL here I think.
Yeah, makes sense, if there is a GPU process, it will have at-least one page table entry.

+            amdgpu_vm_pt_free(entry);
+    }
  }
    /**
@@ -972,10 +968,24 @@ int amdgpu_vm_ptes_update(struct amdgpu_vm_update_params *params,
              while (cursor.pfn < frag_start) {
                  /* Make sure previous mapping is freed */
                  if (cursor.entry->bo) {
+                    struct amdgpu_vm_pt_cursor seek;
+                    struct amdgpu_vm_bo_base *entry;
+
                      params->needs_flush = true;
-                    amdgpu_vm_pt_free_dfs(adev, params->vm,
-                                  &cursor,
-                                  params->unlocked);
+ spin_lock(&params->vm->status_lock);
+                    for_each_amdgpu_vm_pt_dfs_safe(adev, params->vm, &cursor,
+                                       seek, entry) {
+                        if (!entry || !entry->bo)
+                            continue;
+
+                        list_move(&entry->vm_status,
+ &params->tlb_flush_waitlist);
+                    }
+
+                    /* enter start node now */
+                    list_move(&cursor.entry->vm_status,
+                          &params->tlb_flush_waitlist);
+ spin_unlock(&params->vm->status_lock);

I would put this into a separate function maybe.

Noted,

- Shashank


Apart from those nit-picks looks good to me.

Regards,
Christian.

                  }
                  amdgpu_vm_pt_next(adev, &cursor);
              }




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