Re: [PATCH v6 02/20] drm/xe: Strict migration policy for atomic SVM faults

Hi, Himal,

On Wed, 2025-04-30 at 17:48 +0530, Himal Prasad Ghimiray wrote:

From: Matthew Brost matthew.brost@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@vger.kernel.org Signed-off-by: Himal Prasad Ghimiray himal.prasad.ghimiray@intel.com Signed-off-by: Matthew Brost matthew.brost@intel.com Acked-by: Himal Prasad Ghimiray himal.prasad.ghimiray@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.ca...

(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;

};    /**