[PATCH v6 2/5] drm/xe: Strict migration policy for atomic SVM faults
Thomas Hellström
thomas.hellstrom at linux.intel.com
Wed May 7 12:01:56 UTC 2025
This is v7, right? (Says v6 in the subject).
On Tue, 2025-05-06 at 16:01 -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 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)
> v7:
> - Pair READ_ONCE with WRITE_ONCE (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/drm_gpusvm.c | 23 +++++--
> drivers/gpu/drm/xe/xe_module.c | 3 -
> drivers/gpu/drm/xe/xe_module.h | 1 -
> drivers/gpu/drm/xe/xe_pt.c | 14 ++++-
> drivers/gpu/drm/xe/xe_svm.c | 109 +++++++++++++++++++++++++------
> --
> drivers/gpu/drm/xe/xe_svm.h | 5 --
> include/drm/drm_gpusvm.h | 40 +++++++-----
> 7 files changed, 138 insertions(+), 57 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_gpusvm.c
> b/drivers/gpu/drm/drm_gpusvm.c
> index a58d03e6cac2..41f6616bcf76 100644
> --- a/drivers/gpu/drm/drm_gpusvm.c
> +++ b/drivers/gpu/drm/drm_gpusvm.c
> @@ -1118,6 +1118,10 @@ static void
> __drm_gpusvm_range_unmap_pages(struct drm_gpusvm *gpusvm,
> lockdep_assert_held(&gpusvm->notifier_lock);
>
> if (range->flags.has_dma_mapping) {
> + struct drm_gpusvm_range_flags flags = {
> + .__flags = range->flags.__flags,
> + };
> +
> for (i = 0, j = 0; i < npages; j++) {
> struct drm_pagemap_device_addr *addr =
> &range->dma_addr[j];
>
> @@ -1131,8 +1135,12 @@ static void
> __drm_gpusvm_range_unmap_pages(struct drm_gpusvm *gpusvm,
> dev,
> *addr);
> i += 1 << addr->order;
> }
> - range->flags.has_devmem_pages = false;
> - range->flags.has_dma_mapping = false;
> +
> + /* WRITE_ONCE pairs with READ_ONCE for opportunistic
> checks */
> + flags.has_devmem_pages = false;
> + flags.has_dma_mapping = false;
> + WRITE_ONCE(range->flags.__flags, flags.__flags);
> +
> range->dpagemap = NULL;
> }
> }
> @@ -1334,6 +1342,7 @@ int drm_gpusvm_range_get_pages(struct
> drm_gpusvm *gpusvm,
> int err = 0;
> struct dev_pagemap *pagemap;
> struct drm_pagemap *dpagemap;
> + struct drm_gpusvm_range_flags flags;
>
> retry:
> hmm_range.notifier_seq = mmu_interval_read_begin(notifier);
> @@ -1378,7 +1387,8 @@ int drm_gpusvm_range_get_pages(struct
> drm_gpusvm *gpusvm,
> */
> drm_gpusvm_notifier_lock(gpusvm);
>
> - if (range->flags.unmapped) {
> + flags.__flags = range->flags.__flags;
> + if (flags.unmapped) {
> drm_gpusvm_notifier_unlock(gpusvm);
> err = -EFAULT;
> goto err_free;
> @@ -1474,14 +1484,17 @@ int drm_gpusvm_range_get_pages(struct
> drm_gpusvm *gpusvm,
> }
> i += 1 << order;
> num_dma_mapped = i;
> - range->flags.has_dma_mapping = true;
> + flags.has_dma_mapping = true;
> }
>
> if (zdd) {
> - range->flags.has_devmem_pages = true;
> + flags.has_devmem_pages = true;
> range->dpagemap = dpagemap;
> }
>
> + /* WRITE_ONCE pairs with READ_ONCE for opportunistic checks
> */
> + WRITE_ONCE(range->flags.__flags, flags.__flags);
> +
> drm_gpusvm_notifier_unlock(gpusvm);
> kvfree(pfns);
> set_seqno:
> 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_pt.c b/drivers/gpu/drm/xe/xe_pt.c
> index b42cf5d1b20c..b487e094178d 100644
> --- a/drivers/gpu/drm/xe/xe_pt.c
> +++ b/drivers/gpu/drm/xe/xe_pt.c
> @@ -2270,11 +2270,19 @@ static void op_commit(struct xe_vm *vm,
> }
> case DRM_GPUVA_OP_DRIVER:
> {
> + /* WRITE_ONCE pairs with READ_ONCE opportunistic
> checks */
> +
> if (op->subop == XE_VMA_SUBOP_MAP_RANGE) {
> - op->map_range.range->tile_present |=
> BIT(tile->id);
> - op->map_range.range->tile_invalidated &=
> ~BIT(tile->id);
> + WRITE_ONCE(op->map_range.range-
> >tile_present,
> + op->map_range.range->tile_present
> |
> + BIT(tile->id));
> + WRITE_ONCE(op->map_range.range-
> >tile_invalidated,
> + op->map_range.range-
> >tile_invalidated &
> + ~BIT(tile->id));
> } else if (op->subop == XE_VMA_SUBOP_UNMAP_RANGE) {
> - op->unmap_range.range->tile_present &=
> ~BIT(tile->id);
> + WRITE_ONCE(op->unmap_range.range-
> >tile_present,
> + op->unmap_range.range-
> >tile_present &
> + ~BIT(tile->id));
> }
> break;
> }
> diff --git a/drivers/gpu/drm/xe/xe_svm.c
> b/drivers/gpu/drm/xe/xe_svm.c
> index 890f6b2f40e9..8c0ef55cfd57 100644
> --- a/drivers/gpu/drm/xe/xe_svm.c
> +++ b/drivers/gpu/drm/xe/xe_svm.c
> @@ -16,8 +16,15 @@
>
So what I meant in the review comments is something along
/* Advisory only check whether the range is currently backed by VRAM
memory. */
(As said we shouldn need to look at the function implementation to
understand that it's opportunistic).
> 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,
> pairs with
> + * WRITE_ONCE
So if we assume that this function should is never be called with the
notifier lock held, we can leave that comment out, just
/* Pairs with WRITE_ONCE() in xe_pt.c */
And similar for the other places.
Thanks,
Thomas
> + */
> + 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 +657,16 @@ 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,
> pairs with
> + * WRITE_ONCE
> + */
> + return ((READ_ONCE(range->tile_present) &
> + ~READ_ONCE(range->tile_invalidated)) & BIT(tile-
> >id)) &&
> + (!devmem_only || xe_svm_range_in_vram(range));
> }
>
> #if IS_ENABLED(CONFIG_DRM_XE_DEVMEM_MIRROR)
> @@ -726,6 +740,36 @@ 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 +794,15 @@ 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 +823,30 @@ 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 +854,22 @@ 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 +903,6 @@ 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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