Re: [PATCH 1/2] drm/amdkfd: set prefetch GPU has access attribute

[Felix Kuehling <felix.kuehling@amd.com>]

Am 2021-05-05 um 1:56 p.m. schrieb Philip Yang:
> After svm range prefetch and migrate to GPU, if GPU has no access or
> access in place attribute, add GPU to range access_bitmap to be able to
> update GPU page table.

I don't think we should change the bitmap_access, because this is
persistent and can be queried by user mode. Changing this would not be
expected by the application. I think instead we should either pass the
prefetch location to the gpuidx parameter of validate_and_map (we should
only do that is xnack is enabled), or change the logic in
validate_and_map to add the prefetch location to the bitmap.

I think to make this reliable we'll need to add more sanity checks to
prefetch to make sure the prefetch location is compatible with all GPUs
that have access_in_place. Otherwise we have to reject the prefetch.

Regards,
  Felix


>
> Signed-off-by: Philip Yang <Philip.Yang@amd.com>
> ---
>  drivers/gpu/drm/amd/amdkfd/kfd_svm.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
>
> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
> index d9111fea724b..3b640772d9c5 100644
> --- a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
> @@ -2869,6 +2869,17 @@ svm_range_set_attr(struct kfd_process *p, uint64_t start, uint64_t size,
>  			continue;
>  		}
>  
> +		if (migrated && prange->prefetch_loc) {
> +			int gpuidx;
> +
> +			gpuidx = kfd_process_gpuidx_from_gpuid(p,
> +							prange->prefetch_loc);
> +			if (gpuidx >= 0 &&
> +			    !test_bit(gpuidx, prange->bitmap_access) &&
> +			    !test_bit(gpuidx, prange->bitmap_aip))
> +				bitmap_set(prange->bitmap_access, gpuidx, 1);
> +		}
> +
>  		r = svm_range_validate_and_map(mm, prange, MAX_GPU_INSTANCE,
>  					       true, true);
>  		if (r)
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