[PATCH v6 02/20] drm/xe: Strict migration policy for atomic SVM faults
Thomas Hellström
thomas.hellstrom at linux.intel.com
Mon May 5 15:20:00 UTC 2025
Hi, Himal,
On Wed, 2025-04-30 at 17:48 +0530, Himal Prasad Ghimiray wrote:
> From: Matthew Brost <matthew.brost at intel.com>
>
> 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 3 attempts, if retry loop fails abort
> fault.
>
> Removing always_migrate_to_vram modparam as we now have real
> migration
> policy.
>
> 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
> v5:
> - Fix commit message (Himal)
> - Mention removing always_migrate_to_vram in commit message (Lucas)
> - Fix xe_svm_range_is_valid to check for devmem pages
> - Bail on devmem_only && !migrate_devmem (Thomas)
> v6:
> - Add READ_ONCE barriers for opportunistic checks (Thomas)
>
> Fixes: 2f118c949160 ("drm/xe: Add SVM VRAM migration")
> Cc: stable at vger.kernel.org
> Signed-off-by: Himal Prasad Ghimiray
> <himal.prasad.ghimiray at intel.com>
> Signed-off-by: Matthew Brost <matthew.brost at intel.com>
> Acked-by: Himal Prasad Ghimiray <himal.prasad.ghimiray at 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 | 103 ++++++++++++++++++++++++-------
> --
> drivers/gpu/drm/xe/xe_svm.h | 5 --
> include/drm/drm_gpusvm.h | 40 ++++++++-----
> 5 files changed, 103 insertions(+), 49 deletions(-)
>
> diff --git a/drivers/gpu/drm/xe/xe_module.c
> b/drivers/gpu/drm/xe/xe_module.c
> index 64bf46646544..e4742e27e2cd 100644
> --- a/drivers/gpu/drm/xe/xe_module.c
> +++ b/drivers/gpu/drm/xe/xe_module.c
> @@ -30,9 +30,6 @@ 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..dcc84e65ca96 100644
> --- a/drivers/gpu/drm/xe/xe_svm.c
> +++ b/drivers/gpu/drm/xe/xe_svm.c
> @@ -16,8 +16,12 @@
>
> static bool xe_svm_range_in_vram(struct xe_svm_range *range)
> {
> - /* Not reliable without notifier lock */
> - return range->base.flags.has_devmem_pages;
> + /* Not reliable without notifier lock, opportunistic only */
> + struct drm_gpusvm_range_flags flags = {
> + .__flags = READ_ONCE(range->base.flags.__flags),
> + };
> +
> + return flags.has_devmem_pages;
> }
>
> static bool xe_svm_range_has_vram_binding(struct xe_svm_range
> *range)
> @@ -650,9 +654,13 @@ 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);
> + /* Not reliable without notifier lock, opportunistic only */
> + return ((READ_ONCE(range->tile_present) &
> + ~READ_ONCE(range->tile_invalidated)) & BIT(tile-
> >id)) &&
> + (!devmem_only || xe_svm_range_in_vram(range));
> }
Hmm, TBH I had something more elaborate in mind:
https://lore.kernel.org/intel-xe/b5569de8cc036e23b976f21a51c4eb5ca104d4bb.camel@linux.intel.com/
(Separate function for lockless access and a lockdep assert for locked
access + similar documentation as the functions I mentioned there + a
"Pairs with" comment.
Thanks,
Thomas
>
> #if IS_ENABLED(CONFIG_DRM_XE_DEVMEM_MIRROR)
> @@ -726,6 +734,36 @@ 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;
> +}
> +
> +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;
> +
> + /* Not reliable without notifier lock, opportunistic only */
> + 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 +788,15 @@ 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;
>
> @@ -776,24 +817,30 @@ int xe_svm_handle_pagefault(struct xe_vm *vm,
> struct xe_vma *vma,
> if (IS_ERR(r))
> return PTR_ERR(r);
>
> + if (ctx.devmem_only && !r->flags.migrate_devmem)
> + return -EACCES;
> +
> range = to_xe_range(r);
> - if (xe_svm_range_is_valid(range, tile))
> + if (xe_svm_range_is_valid(range, tile, ctx.devmem_only))
> 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)) {
> 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 +848,22 @@ 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 +897,6 @@ 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;
> };
>
> /**
> diff --git a/include/drm/drm_gpusvm.h b/include/drm/drm_gpusvm.h
> index 9fd25fc880a4..653d48dbe1c1 100644
> --- a/include/drm/drm_gpusvm.h
> +++ b/include/drm/drm_gpusvm.h
> @@ -185,6 +185,31 @@ struct drm_gpusvm_notifier {
> } flags;
> };
>
> +/**
> + * struct drm_gpusvm_range_flags - Structure representing a GPU SVM
> range flags
> + *
> + * @migrate_devmem: Flag indicating whether the range can be
> migrated to device memory
> + * @unmapped: Flag indicating if the range has been unmapped
> + * @partial_unmap: Flag indicating if the range has been partially
> unmapped
> + * @has_devmem_pages: Flag indicating if the range has devmem pages
> + * @has_dma_mapping: Flag indicating if the range has a DMA mapping
> + * @__flags: Flags for range in u16 form (used for READ_ONCE)
> + */
> +struct drm_gpusvm_range_flags {
> + union {
> + struct {
> + /* All flags below must be set upon creation
> */
> + u16 migrate_devmem : 1;
> + /* All flags below must be set / cleared
> under notifier lock */
> + u16 unmapped : 1;
> + u16 partial_unmap : 1;
> + u16 has_devmem_pages : 1;
> + u16 has_dma_mapping : 1;
> + };
> + u16 __flags;
> + };
> +};
> +
> /**
> * struct drm_gpusvm_range - Structure representing a GPU SVM range
> *
> @@ -198,11 +223,6 @@ struct drm_gpusvm_notifier {
> * @dpagemap: The struct drm_pagemap of the device pages we're dma-
> mapping.
> * Note this is assuming only one drm_pagemap per range
> is allowed.
> * @flags: Flags for range
> - * @flags.migrate_devmem: Flag indicating whether the range can be
> migrated to device memory
> - * @flags.unmapped: Flag indicating if the range has been unmapped
> - * @flags.partial_unmap: Flag indicating if the range has been
> partially unmapped
> - * @flags.has_devmem_pages: Flag indicating if the range has devmem
> pages
> - * @flags.has_dma_mapping: Flag indicating if the range has a DMA
> mapping
> *
> * This structure represents a GPU SVM range used for tracking
> memory ranges
> * mapped in a DRM device.
> @@ -216,15 +236,7 @@ struct drm_gpusvm_range {
> unsigned long notifier_seq;
> struct drm_pagemap_device_addr *dma_addr;
> struct drm_pagemap *dpagemap;
> - struct {
> - /* All flags below must be set upon creation */
> - u16 migrate_devmem : 1;
> - /* All flags below must be set / cleared under
> notifier lock */
> - u16 unmapped : 1;
> - u16 partial_unmap : 1;
> - u16 has_devmem_pages : 1;
> - u16 has_dma_mapping : 1;
> - } flags;
> + struct drm_gpusvm_range_flags flags;
> };
>
> /**
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