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

[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.

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;