On Wed, Oct 29, 2025 at 9:36 PM Harish Kasiviswanathan
<[email protected]> wrote:
>
> Fix the following corner case:-
> Consider a 2M huge page SVM allocation, followed by prefetch call for
> the first 4K page. The whole range is initially mapped with single PTE.
> After the prefetch, this range gets split to first page + rest of the
> pages. Currently, the first page mapping is not updated on MI300A (APU)
> since page hasn't migrated. However, after range split PTE mapping it not
> valid.
>
> Fix this by forcing page table update for the whole range when prefetch
> is called. Calling prefetch on APU doesn't improve performance. If all
> it deteriotes. However, functionality has to be supported.
>
> v2: Use apu_prefer_gtt as this issue doesn't apply to APUs with carveout
> VRAM
apu_prefer_gtt is used by small APUs as well. It depends on how much
VRAM vs GTT is available on the system.
if (adev->flags & AMD_IS_APU) {
if (adev->gmc.real_vram_size < gtt_size)
adev->apu_prefer_gtt = true;
}
Alex
>
> Suggested-by: Philip Yang <[email protected]>
> Signed-off-by: Harish Kasiviswanathan <[email protected]>
> ---
> drivers/gpu/drm/amd/amdkfd/kfd_svm.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
> b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
> index c30dfb8ec236..76cab1c8aaa2 100644
> --- a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
> @@ -766,14 +766,21 @@ svm_range_apply_attrs(struct kfd_process *p, struct
> svm_range *prange,
> {
> uint32_t i;
> int gpuidx;
> + struct kfd_node *node;
>
> for (i = 0; i < nattr; i++) {
> switch (attrs[i].type) {
> case KFD_IOCTL_SVM_ATTR_PREFERRED_LOC:
> prange->preferred_loc = attrs[i].value;
> + node = svm_range_get_node_by_id(prange,
> attrs[i].value);
> + if (node && node->adev->apu_prefer_gtt &&
> !p->xnack_enabled)
> + *update_mapping = true;
> break;
> case KFD_IOCTL_SVM_ATTR_PREFETCH_LOC:
> prange->prefetch_loc = attrs[i].value;
> + node = svm_range_get_node_by_id(prange,
> attrs[i].value);
> + if (node && node->adev->apu_prefer_gtt &&
> !p->xnack_enabled)
> + *update_mapping = true;
> break;
> case KFD_IOCTL_SVM_ATTR_ACCESS:
> case KFD_IOCTL_SVM_ATTR_ACCESS_IN_PLACE:
> --
> 2.34.1
>
