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

["Sharma, Shashank" <shashank.sharma@amd.com>]

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@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>
>> Tested-by: Rajneesh Bhardwaj <rajneesh.bhardwaj@amd.com>
>> Signed-off-by: Shashank Sharma <shashank.sharma@amd.com>
>> ---
>>   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);
>>               }
>