On Tue, 2025-04-22 at 10:04 -0700, Matthew Brost wrote:
> Mixing GPU and CPU atomics does not work unless a strict migration
> policy of GPU atomics must be device memory. Enforce a policy of must
> be
> in VRAM with a retry loop of 2 attempts, if retry loop fails abort
> fault.
>
> v2:
> - Only retry migration on atomics
> - Drop alway migrate modparam
> v3:
> - Only set vram_only on DGFX (Himal)
> - Bail on get_pages failure if vram_only and retry count exceeded
> (Himal)
> - s/vram_only/devmem_only
> - Update xe_svm_range_is_valid to accept devmem_only argument
> v4:
> - Fix logic bug get_pages failure
>
> Signed-off-by: Himal Prasad Ghimiray
> <himal.prasad.ghimi...@intel.com>
> Signed-off-by: Matthew Brost <matthew.br...@intel.com>
> ---
> drivers/gpu/drm/xe/xe_module.c | 3 --
> drivers/gpu/drm/xe/xe_module.h | 1 -
> drivers/gpu/drm/xe/xe_svm.c | 89 +++++++++++++++++++++++++-------
> --
> drivers/gpu/drm/xe/xe_svm.h | 5 --
> 4 files changed, 65 insertions(+), 33 deletions(-)
>
> diff --git a/drivers/gpu/drm/xe/xe_module.c
> b/drivers/gpu/drm/xe/xe_module.c
> index 05c7d0ae6d83..1c4dfafbcd0b 100644
> --- a/drivers/gpu/drm/xe/xe_module.c
> +++ b/drivers/gpu/drm/xe/xe_module.c
> @@ -33,9 +33,6 @@ struct xe_modparam xe_modparam = {
> module_param_named(svm_notifier_size, xe_modparam.svm_notifier_size,
> uint, 0600);
> MODULE_PARM_DESC(svm_notifier_size, "Set the svm notifier size(in
> MiB), must be power of 2");
>
> -module_param_named(always_migrate_to_vram,
> xe_modparam.always_migrate_to_vram, bool, 0444);
> -MODULE_PARM_DESC(always_migrate_to_vram, "Always migrate to VRAM on
> GPU fault");
> -
module_param_named_unsafe(force_execlist,
> xe_modparam.force_execlist, bool, 0444);
> MODULE_PARM_DESC(force_execlist, "Force Execlist submission");
>
> diff --git a/drivers/gpu/drm/xe/xe_module.h
> b/drivers/gpu/drm/xe/xe_module.h
> index 84339e509c80..5a3bfea8b7b4 100644
> --- a/drivers/gpu/drm/xe/xe_module.h
> +++ b/drivers/gpu/drm/xe/xe_module.h
> @@ -12,7 +12,6 @@
> struct xe_modparam {
> bool force_execlist;
> bool probe_display;
> - bool always_migrate_to_vram;
> u32 force_vram_bar_size;
> int guc_log_level;
> char *guc_firmware_path;
> diff --git a/drivers/gpu/drm/xe/xe_svm.c
> b/drivers/gpu/drm/xe/xe_svm.c
> index 890f6b2f40e9..f749ae367a8f 100644
> --- a/drivers/gpu/drm/xe/xe_svm.c
> +++ b/drivers/gpu/drm/xe/xe_svm.c
> @@ -650,9 +650,11 @@ void xe_svm_fini(struct xe_vm *vm)
> }
>
> static bool xe_svm_range_is_valid(struct xe_svm_range *range,
> - struct xe_tile *tile)
> + struct xe_tile *tile,
> + bool devmem_only)
> {
> - return (range->tile_present & ~range->tile_invalidated) &
> BIT(tile->id);
> + return ((range->tile_present & ~range->tile_invalidated) &
> BIT(tile->id))
> + && (!devmem_only || range-
> >base.flags.migrate_devmem);
> }
So let's say devmem_only is true here, and range-
>base.flags.migrate_devmem is false. Wouldn't that mean the range is
unusable and needs to be freed and re-allocated?
Also another thing going back to older code, it seems like range-
>tile_invalidated is protected by the notifier lock, so shouldn't we
assert that to be held in the function? It seems not to be held further
below:
>
> #if IS_ENABLED(CONFIG_DRM_XE_DEVMEM_MIRROR)
> @@ -726,6 +728,35 @@ static int xe_svm_alloc_vram(struct xe_vm *vm,
> struct xe_tile *tile,
> }
> #endif
>
> +static bool supports_4K_migration(struct xe_device *xe)
> +{
> + if (xe->info.vram_flags & XE_VRAM_FLAGS_NEED64K)
> + return false;
> +
> + return true;
> +}
Do we have any hardware that supports pagefaults but not 4K VRAM pages?
> +
> +static bool xe_svm_range_needs_migrate_to_vram(struct xe_svm_range
> *range,
> + struct xe_vma *vma)
> +{
> + struct xe_vm *vm = range_to_vm(&range->base);
> + u64 range_size = xe_svm_range_size(range);
> +
> + if (!range->base.flags.migrate_devmem)
> + return false;
> +
> + if (xe_svm_range_in_vram(range)) {
> + drm_dbg(&vm->xe->drm, "Range is already in VRAM\n");
> + return false;
> + }
> +
> + if (range_size <= SZ_64K && !supports_4K_migration(vm->xe))
> {
> + drm_dbg(&vm->xe->drm, "Platform doesn't support
> SZ_4K range migration\n");
> + return false;
> + }
> +
> + return true;
> +}
>
> /**
> * xe_svm_handle_pagefault() - SVM handle page fault
> @@ -750,12 +781,15 @@ int xe_svm_handle_pagefault(struct xe_vm *vm,
> struct xe_vma *vma,
> IS_ENABLED(CONFIG_DRM_XE_DEVMEM_MIRROR),
> .check_pages_threshold = IS_DGFX(vm->xe) &&
> IS_ENABLED(CONFIG_DRM_XE_DEVMEM_MIRROR) ?
> SZ_64K : 0,
> + .devmem_only = atomic && IS_DGFX(vm->xe) &&
> + IS_ENABLED(CONFIG_DRM_XE_DEVMEM_MIRROR),
> };
> struct xe_svm_range *range;
> struct drm_gpusvm_range *r;
> struct drm_exec exec;
> struct dma_fence *fence;
> struct xe_tile *tile = gt_to_tile(gt);
> + int migrate_try_count = ctx.devmem_only ? 3 : 1;
> ktime_t end = 0;
> int err;
>
> @@ -777,23 +811,26 @@ int xe_svm_handle_pagefault(struct xe_vm *vm,
> struct xe_vma *vma,
> return PTR_ERR(r);
>
> range = to_xe_range(r);
> - if (xe_svm_range_is_valid(range, tile))
> + if (xe_svm_range_is_valid(range, tile, ctx.devmem_only))
Requires notifier lock. Also see comment on re-allocating the range
above.
> return 0;
>
> range_debug(range, "PAGE FAULT");
>
> - /* XXX: Add migration policy, for now migrate range once */
> - if (!range->skip_migrate && range->base.flags.migrate_devmem
> &&
> - xe_svm_range_size(range) >= SZ_64K) {
> - range->skip_migrate = true;
> -
> + if (--migrate_try_count >= 0 &&
> + xe_svm_range_needs_migrate_to_vram(range, vma)
Requires notifier lock.
Should we have some sort of timeout instead of a try-count? Perhaps as
a last resort fall back to a 4K range?
/Thomas
> ) {
> err = xe_svm_alloc_vram(vm, tile, range, &ctx);
> if (err) {
> - drm_dbg(&vm->xe->drm,
> - "VRAM allocation failed, falling
> back to "
> - "retrying fault, asid=%u,
> errno=%pe\n",
> - vm->usm.asid, ERR_PTR(err));
> - goto retry;
> + if (migrate_try_count || !ctx.devmem_only) {
> + drm_dbg(&vm->xe->drm,
> + "VRAM allocation failed,
> falling back to retrying fault, asid=%u, errno=%pe\n",
> + vm->usm.asid, ERR_PTR(err));
> + goto retry;
> + } else {
> + drm_err(&vm->xe->drm,
> + "VRAM allocation failed,
> retry count exceeded, asid=%u, errno=%pe\n",
> + vm->usm.asid, ERR_PTR(err));
> + return err;
> + }
> }
> }
>
> @@ -801,15 +838,22 @@ int xe_svm_handle_pagefault(struct xe_vm *vm,
> struct xe_vma *vma,
> err = drm_gpusvm_range_get_pages(&vm->svm.gpusvm, r, &ctx);
> /* Corner where CPU mappings have changed */
> if (err == -EOPNOTSUPP || err == -EFAULT || err == -EPERM) {
> - if (err == -EOPNOTSUPP) {
> - range_debug(range, "PAGE FAULT - EVICT
> PAGES");
> - drm_gpusvm_range_evict(&vm->svm.gpusvm,
> &range->base);
> + if (migrate_try_count > 0 || !ctx.devmem_only) {
> + if (err == -EOPNOTSUPP) {
> + range_debug(range, "PAGE FAULT -
> EVICT PAGES");
> + drm_gpusvm_range_evict(&vm-
> >svm.gpusvm,
> + &range-
> >base);
> + }
> + drm_dbg(&vm->xe->drm,
> + "Get pages failed, falling back to
> retrying, asid=%u, gpusvm=%p, errno=%pe\n",
> + vm->usm.asid, &vm->svm.gpusvm,
> ERR_PTR(err));
> + range_debug(range, "PAGE FAULT - RETRY
> PAGES");
> + goto retry;
> + } else {
> + drm_err(&vm->xe->drm,
> + "Get pages failed, retry count
> exceeded, asid=%u, gpusvm=%p, errno=%pe\n",
> + vm->usm.asid, &vm->svm.gpusvm,
> ERR_PTR(err));
> }
> - drm_dbg(&vm->xe->drm,
> - "Get pages failed, falling back to retrying,
> asid=%u, gpusvm=%p, errno=%pe\n",
> - vm->usm.asid, &vm->svm.gpusvm,
> ERR_PTR(err));
> - range_debug(range, "PAGE FAULT - RETRY PAGES");
> - goto retry;
> }
> if (err) {
> range_debug(range, "PAGE FAULT - FAIL PAGE
> COLLECT");
> @@ -843,9 +887,6 @@ int xe_svm_handle_pagefault(struct xe_vm *vm,
> struct xe_vma *vma,
> }
> drm_exec_fini(&exec);
>
> - if (xe_modparam.always_migrate_to_vram)
> - range->skip_migrate = false;
> -
> dma_fence_wait(fence, false);
> dma_fence_put(fence);
>
> diff --git a/drivers/gpu/drm/xe/xe_svm.h
> b/drivers/gpu/drm/xe/xe_svm.h
> index 3d441eb1f7ea..0e1f376a7471 100644
> --- a/drivers/gpu/drm/xe/xe_svm.h
> +++ b/drivers/gpu/drm/xe/xe_svm.h
> @@ -39,11 +39,6 @@ struct xe_svm_range {
> * range. Protected by GPU SVM notifier lock.
> */
> u8 tile_invalidated;
> - /**
> - * @skip_migrate: Skip migration to VRAM, protected by GPU
> fault handler
> - * locking.
> - */
> - u8 skip_migrate :1;
> };
>
> /**
