[PATCH 1/1] drm/amdgpu: Sync with VM root BO when switching VM to CPU update mode

[Felix Kuehling]

Am 2020-05-21 um 9:50 a.m. schrieb Christian König:
> Am 21.05.20 um 00:51 schrieb Felix Kuehling:
>> This fixes an intermittent bug where a root PD clear operation still in
>> progress could overwrite a PDE update done by the CPU, resulting in a
>> VM fault.
>
> Mhm, maybe better add this to amdgpu_vm_cpu_prepare().
>
> This way we could (in theory) switch between CPU and SDMA based
> updates on the fly elsewhere as well.

That won't work. I want to wait for FENCE_OWNER_VM fences, so I need to
use FENCE_OWNER_UNDEFINED. But then I would also end up waiting for
FENCE_OWNER_KFD eviction fences, which would trigger unwanted evictions.

This works OK in amdgpu_vm_make_compute because it runs before the
eviction fence is attached to the VM.

Regards,
  Felix


>
> Christian.
>
>>
>> Fixes: 108b4d928c03 ("drm/amd/amdgpu: Update VM function pointer")
>> Reported-by: Jay Cornwall <Jay.Cornwall at amd.com>
>> Tested-by: Jay Cornwall <Jay.Cornwall at amd.com>
>> Signed-off-by: Felix Kuehling <Felix.Kuehling at amd.com>
>> ---
>>   drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 11 +++++++++--
>>   1 file changed, 9 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>> index 414a0b1c2e5a..7417754e9141 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>> @@ -3000,10 +3000,17 @@ int amdgpu_vm_make_compute(struct
>> amdgpu_device *adev, struct amdgpu_vm *vm,
>>              !amdgpu_gmc_vram_full_visible(&adev->gmc)),
>>             "CPU update of VM recommended only for large BAR system\n");
>>   -    if (vm->use_cpu_for_update)
>> +    if (vm->use_cpu_for_update) {
>> +        /* Sync with last SDMA update/clear before switching to CPU */
>> +        r = amdgpu_bo_sync_wait(vm->root.base.bo,
>> +                    AMDGPU_FENCE_OWNER_UNDEFINED, true);
>> +        if (r)
>> +            goto free_idr;
>> +
>>           vm->update_funcs = &amdgpu_vm_cpu_funcs;
>> -    else
>> +    } else {
>>           vm->update_funcs = &amdgpu_vm_sdma_funcs;
>> +    }
>>       dma_fence_put(vm->last_update);
>>       vm->last_update = NULL;
>>       vm->is_compute_context = true;
>