[PATCH v2] drm/amdkfd: reserve the BO before validating it

Yu, Lang Lang.Yu at amd.com
Mon Jan 29 02:30:48 UTC 2024


[AMD Official Use Only - General]

>-----Original Message-----
>From: Kuehling, Felix <Felix.Kuehling at amd.com>
>Sent: Saturday, January 27, 2024 3:22 AM
>To: Yu, Lang <Lang.Yu at amd.com>; amd-gfx at lists.freedesktop.org
>Cc: Francis, David <David.Francis at amd.com>
>Subject: Re: [PATCH v2] drm/amdkfd: reserve the BO before validating it
>
>
>On 2024-01-25 20:59, Yu, Lang wrote:
>> [AMD Official Use Only - General]
>>
>>> -----Original Message-----
>>> From: Kuehling, Felix <Felix.Kuehling at amd.com>
>>> Sent: Thursday, January 25, 2024 5:41 AM
>>> To: Yu, Lang <Lang.Yu at amd.com>; amd-gfx at lists.freedesktop.org
>>> Cc: Francis, David <David.Francis at amd.com>
>>> Subject: Re: [PATCH v2] drm/amdkfd: reserve the BO before validating
>>> it
>>>
>>> On 2024-01-22 4:08, Lang Yu wrote:
>>>> Fixes: 410f08516e0f ("drm/amdkfd: Move dma unmapping after TLB
>>>> flush")
>>>>
>>>> v2:
>>>> Avoid unmapping attachment twice when ERESTARTSYS.
>>>>
>>>> [   41.708711] WARNING: CPU: 0 PID: 1463 at
>>> drivers/gpu/drm/ttm/ttm_bo.c:846 ttm_bo_validate+0x146/0x1b0 [ttm]
>>>> [   41.708989] Call Trace:
>>>> [   41.708992]  <TASK>
>>>> [   41.708996]  ? show_regs+0x6c/0x80
>>>> [   41.709000]  ? ttm_bo_validate+0x146/0x1b0 [ttm]
>>>> [   41.709008]  ? __warn+0x93/0x190
>>>> [   41.709014]  ? ttm_bo_validate+0x146/0x1b0 [ttm]
>>>> [   41.709024]  ? report_bug+0x1f9/0x210
>>>> [   41.709035]  ? handle_bug+0x46/0x80
>>>> [   41.709041]  ? exc_invalid_op+0x1d/0x80
>>>> [   41.709048]  ? asm_exc_invalid_op+0x1f/0x30
>>>> [   41.709057]  ? amdgpu_amdkfd_gpuvm_dmaunmap_mem+0x2c/0x80
>>> [amdgpu]
>>>> [   41.709185]  ? ttm_bo_validate+0x146/0x1b0 [ttm]
>>>> [   41.709197]  ? amdgpu_amdkfd_gpuvm_dmaunmap_mem+0x2c/0x80
>>> [amdgpu]
>>>> [   41.709337]  ? srso_alias_return_thunk+0x5/0x7f
>>>> [   41.709346]  kfd_mem_dmaunmap_attachment+0x9e/0x1e0 [amdgpu]
>>>> [   41.709467]  amdgpu_amdkfd_gpuvm_dmaunmap_mem+0x56/0x80
>>> [amdgpu]
>>>> [   41.709586]  kfd_ioctl_unmap_memory_from_gpu+0x1b7/0x300 [amdgpu]
>>>> [   41.709710]  kfd_ioctl+0x1ec/0x650 [amdgpu]
>>>> [   41.709822]  ? __pfx_kfd_ioctl_unmap_memory_from_gpu+0x10/0x10
>>> [amdgpu]
>>>> [   41.709945]  ? srso_alias_return_thunk+0x5/0x7f
>>>> [   41.709949]  ? tomoyo_file_ioctl+0x20/0x30
>>>> [   41.709959]  __x64_sys_ioctl+0x9c/0xd0
>>>> [   41.709967]  do_syscall_64+0x3f/0x90
>>>> [   41.709973]  entry_SYSCALL_64_after_hwframe+0x6e/0xd8
>>>>
>>>> Signed-off-by: Lang Yu <Lang.Yu at amd.com>
>>>> ---
>>>>    drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h    |  2 +-
>>>>    .../gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c  | 28
>>> +++++++++++++++++--
>>>>    drivers/gpu/drm/amd/amdkfd/kfd_chardev.c      |  4 ++-
>>>>    3 files changed, 29 insertions(+), 5 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h
>>>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h
>>>> index 584a0cea5572..41854417e487 100644
>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h
>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h
>>>> @@ -311,7 +311,7 @@ int
>>> amdgpu_amdkfd_gpuvm_map_memory_to_gpu(struct amdgpu_device *adev,
>>>>                                         struct kgd_mem *mem, void
>>> *drm_priv);
>>>>    int amdgpu_amdkfd_gpuvm_unmap_memory_from_gpu(
>>>>               struct amdgpu_device *adev, struct kgd_mem *mem, void
>>> *drm_priv);
>>>> -void amdgpu_amdkfd_gpuvm_dmaunmap_mem(struct kgd_mem *mem, void
>>>> *drm_priv);
>>>> +int amdgpu_amdkfd_gpuvm_dmaunmap_mem(struct kgd_mem *mem, void
>>>> +*drm_priv);
>>>>    int amdgpu_amdkfd_gpuvm_sync_memory(
>>>>               struct amdgpu_device *adev, struct kgd_mem *mem, bool intr);
>>>>    int amdgpu_amdkfd_gpuvm_map_gtt_bo_to_kernel(struct kgd_mem *mem,
>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
>>>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
>>>> index 6f3a4cb2a9ef..7a050d46fa4d 100644
>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
>>>> @@ -2088,21 +2088,43 @@ int
>>> amdgpu_amdkfd_gpuvm_map_memory_to_gpu(
>>>>       return ret;
>>>>    }
>>>>
>>>> -void amdgpu_amdkfd_gpuvm_dmaunmap_mem(struct kgd_mem *mem, void
>>>> *drm_priv)
>>>> +int amdgpu_amdkfd_gpuvm_dmaunmap_mem(struct kgd_mem *mem, void
>>>> +*drm_priv)
>>>>    {
>>>>       struct kfd_mem_attachment *entry;
>>>>       struct amdgpu_vm *vm;
>>>> +    bool reserved = false;
>>>> +    int ret = 0;
>>>>
>>>>       vm = drm_priv_to_vm(drm_priv);
>>>>
>>>>       mutex_lock(&mem->lock);
>>>>
>>>>       list_for_each_entry(entry, &mem->attachments, list) {
>>>> -            if (entry->bo_va->base.vm == vm)
>>>> -                    kfd_mem_dmaunmap_attachment(mem, entry);
>>>> +            if (entry->bo_va->base.vm != vm)
>>>> +                    continue;
>>>> +            if (entry->type == KFD_MEM_ATT_SHARED ||
>>>> +                entry->type == KFD_MEM_ATT_DMABUF)
>>>> +                    continue;
>>>> +            if (!entry->bo_va->base.bo->tbo.ttm->sg)
>>>> +                    continue;
>>> You're going to great lengths to avoid the reservation when it's not
>>> needed by kfd_mem_dmaunmap_attachment. However, this feels a bit
>>> fragile. Any changes in the kfd_mem_dmaunmap_* functions could break this.
>>>
>>>> +
>>>> +            if (!reserved) {
>>>> +                    ret = amdgpu_bo_reserve(mem->bo, true);
>>>> +                    if (ret)
>>>> +                            goto out;
>>>> +                    reserved = true;
>>>> +            }
>>>> +
>>>> +            kfd_mem_dmaunmap_attachment(mem, entry);
>>>>       }
>>>>
>>>> +    if (reserved)
>>>> +            amdgpu_bo_unreserve(mem->bo);
>>>> +
>>>> +out:
>>>>       mutex_unlock(&mem->lock);
>>>> +
>>>> +    return ret;
>>>>    }
>>>>
>>>>    int amdgpu_amdkfd_gpuvm_unmap_memory_from_gpu(
>>>> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_chardev.c
>>>> b/drivers/gpu/drm/amd/amdkfd/kfd_chardev.c
>>>> index ce4c52ec34d8..80e90fdef291 100644
>>>> --- a/drivers/gpu/drm/amd/amdkfd/kfd_chardev.c
>>>> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_chardev.c
>>>> @@ -1442,7 +1442,9 @@ static int
>>>> kfd_ioctl_unmap_memory_from_gpu(struct
>>> file *filep,
>>>>                       kfd_flush_tlb(peer_pdd,
>>>> TLB_FLUSH_HEAVYWEIGHT);
>>>>
>>>>               /* Remove dma mapping after tlb flush to avoid
>>>> IO_PAGE_FAULT
>>> */
>>>> -            amdgpu_amdkfd_gpuvm_dmaunmap_mem(mem, peer_pdd-
>>>> drm_priv);
>>>> +            err = amdgpu_amdkfd_gpuvm_dmaunmap_mem(mem,
>>> peer_pdd->drm_priv);
>>>> +            if (err)
>>>> +                    goto sync_memory_failed;
>>> This handles the case that the system call got interrupted. But
>>> you're not handling the restart correctly. When the ioctl is
>>> restarted, you don't know how many dmaunmaps are already done. So
>>> you'd need to make sure that repeating the dmaunmap is safe in all
>>> cases. Or what David tried earlier, find a way to track the unmapping so you
>only try to dmaunmap on GPUs where it's actually dmamapped.
>>  From previous discussion, no one likes add another variable to track the
>unmappings. So I'm avoiding adding another variable.
>>
>> Actually, all memory attachments use sg_table, ttm->sg is NULL? can be used as
>an indicator to see whether an attachment is already unmapped.
>> That already unmapped will not be repeated.
>
>I think that should work. I'd add the checks in kfd_mem_dmaunmap_userptr and
>kfd_mem_dmaunmap_sg_bo, where we also set ttm->sg to NULL. In fact, both
>those functions already have that check. So looks like it should handle the the
>restart correctly with your patch.

Yes, both kfd_mem_dmaunmap_userptr() and kfd_mem_dmaunmap_sg_bo() have NULL check for ttm->sg.

And dmabuf also have this check in amdgpu_ttm_backend_unbind(). So dmaunmap won't be repeated actually.

Then the benefits of handling ERESTARTSYS is avoiding amdgpu_bo_reserve().

What do you think? It's worth avoiding reservation in this case?

Regards,
Lang

>Regards,
>   Felix
>
>
>>
>> Regards,
>> Lang
>>
>>> Regards,
>>>    Felix
>>>
>>>
>>>>       }
>>>>
>>>>       mutex_unlock(&p->mutex);


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