On Mon, 2025-02-24 at 20:43 -0800, Matthew Brost wrote:
> Migration is implemented with range granularity, with VRAM backing
> being
> a VM private TTM BO (i.e., shares dma-resv with VM). The lifetime of
> the
> TTM BO is limited to when the SVM range is in VRAM (i.e., when a VRAM
> SVM range is migrated to SRAM, the TTM BO is destroyed).
>
> The design choice for using TTM BO for VRAM backing store, as opposed
> to
> direct buddy allocation, is as follows:
>
> - DRM buddy allocations are not at page granularity, offering no
> advantage over a BO.
> - Unified eviction is required (SVM VRAM and TTM BOs need to be able
> to
> evict each other).
> - For exhaustive eviction [1], SVM VRAM allocations will almost
> certainly
> require a dma-resv.
> - Likely allocation size is 2M which makes of size of BO (872)
> acceptable per allocation (872 / 2M == .0004158).
>
> With this, using TTM BO for VRAM backing store seems to be an obvious
> choice as it allows leveraging of the TTM eviction code.
>
> Current migration policy is migrate any SVM range greater than or
> equal
> to 64k once.
>
> [1] https://patchwork.freedesktop.org/series/133643/
>
> v2:
> - Rebase on latest GPU SVM
> - Retry page fault on get pages returning mixed allocation
> - Use drm_gpusvm_devmem
> v3:
> - Use new BO flags
> - New range structure (Thomas)
> - Hide migration behind Kconfig
> - Kernel doc (Thomas)
> - Use check_pages_threshold
> v4:
> - Don't evict partial unmaps in garbage collector (Thomas)
> - Use %pe to print errors (Thomas)
> - Use %p to print pointers (Thomas)
> v5:
> - Use range size helper (Thomas)
> - Make BO external (Thomas)
> - Set tile to NULL for BO creation (Thomas)
> - Drop BO mirror flag (Thomas)
> - Hold BO dma-resv lock across migration (Auld, Thomas)
> v6:
> - s/drm_info/drm_dbg (Thomas)
> - s/migrated/skip_migrate (Himal)
> - Better debug message on VRAM migration failure (Himal)
> - Drop return BO from VRAM allocation function (Thomas)
>
> Signed-off-by: Matthew Brost <matthew.br...@intel.com>
Reviewed-by: Thomas Hellström <thomas.hellst...@linux.intel.com>
> ---
> drivers/gpu/drm/xe/xe_svm.c | 97
> +++++++++++++++++++++++++++++++++++--
> drivers/gpu/drm/xe/xe_svm.h | 5 ++
> 2 files changed, 98 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/xe/xe_svm.c
> b/drivers/gpu/drm/xe/xe_svm.c
> index cb3567b561be..d8ff7fc708ee 100644
> --- a/drivers/gpu/drm/xe/xe_svm.c
> +++ b/drivers/gpu/drm/xe/xe_svm.c
> @@ -32,6 +32,11 @@ static unsigned long xe_svm_range_end(struct
> xe_svm_range *range)
> return drm_gpusvm_range_end(&range->base);
> }
>
> +static unsigned long xe_svm_range_size(struct xe_svm_range *range)
> +{
> + return drm_gpusvm_range_size(&range->base);
> +}
> +
> static void *xe_svm_devm_owner(struct xe_device *xe)
> {
> return xe;
> @@ -508,7 +513,6 @@ static int xe_svm_populate_devmem_pfn(struct
> drm_gpusvm_devmem *devmem_allocatio
> return 0;
> }
>
> -__maybe_unused
> static const struct drm_gpusvm_devmem_ops gpusvm_devmem_ops = {
> .devmem_release = xe_svm_devmem_release,
> .populate_devmem_pfn = xe_svm_populate_devmem_pfn,
> @@ -588,6 +592,62 @@ static bool xe_svm_range_is_valid(struct
> xe_svm_range *range,
> return (range->tile_present & ~range->tile_invalidated) &
> BIT(tile->id);
> }
>
> +static struct xe_vram_region *tile_to_vr(struct xe_tile *tile)
> +{
> + return &tile->mem.vram;
> +}
> +
> +static int xe_svm_alloc_vram(struct xe_vm *vm, struct xe_tile *tile,
> + struct xe_svm_range *range,
> + const struct drm_gpusvm_ctx *ctx)
> +{
> + struct mm_struct *mm = vm->svm.gpusvm.mm;
> + struct xe_vram_region *vr = tile_to_vr(tile);
> + struct drm_buddy_block *block;
> + struct list_head *blocks;
> + struct xe_bo *bo;
> + ktime_t end = 0;
> + int err;
> +
> + if (!mmget_not_zero(mm))
> + return -EFAULT;
> + mmap_read_lock(mm);
> +
> +retry:
> + bo = xe_bo_create_locked(tile_to_xe(tile), NULL, NULL,
> + xe_svm_range_size(range),
> + ttm_bo_type_device,
> + XE_BO_FLAG_VRAM_IF_DGFX(tile));
> + if (IS_ERR(bo)) {
> + err = PTR_ERR(bo);
> + if (xe_vm_validate_should_retry(NULL, err, &end))
> + goto retry;
> + goto unlock;
> + }
> +
> + drm_gpusvm_devmem_init(&bo->devmem_allocation,
> + vm->xe->drm.dev, mm,
> + &gpusvm_devmem_ops,
> + &tile->mem.vram.dpagemap,
> + xe_svm_range_size(range));
> +
> + blocks = &to_xe_ttm_vram_mgr_resource(bo->ttm.resource)-
> >blocks;
> + list_for_each_entry(block, blocks, link)
> + block->private = vr;
> +
> + err = drm_gpusvm_migrate_to_devmem(&vm->svm.gpusvm, &range-
> >base,
> + &bo->devmem_allocation,
> ctx);
> + xe_bo_unlock(bo);
> + if (err)
> + xe_bo_put(bo); /* Creation ref */
> +
> +unlock:
> + mmap_read_unlock(mm);
> + mmput(mm);
> +
> + return err;
> +}
> +
> /**
> * xe_svm_handle_pagefault() - SVM handle page fault
> * @vm: The VM.
> @@ -596,7 +656,8 @@ static bool xe_svm_range_is_valid(struct
> xe_svm_range *range,
> * @fault_addr: The GPU fault address.
> * @atomic: The fault atomic access bit.
> *
> - * Create GPU bindings for a SVM page fault.
> + * Create GPU bindings for a SVM page fault. Optionally migrate to
> device
> + * memory.
> *
> * Return: 0 on success, negative error code on error.
> */
> @@ -604,7 +665,13 @@ int xe_svm_handle_pagefault(struct xe_vm *vm,
> struct xe_vma *vma,
> struct xe_tile *tile, u64 fault_addr,
> bool atomic)
> {
> - struct drm_gpusvm_ctx ctx = { .read_only =
> xe_vma_read_only(vma), };
> + struct drm_gpusvm_ctx ctx = {
> + .read_only = xe_vma_read_only(vma),
> + .devmem_possible = IS_DGFX(vm->xe) &&
> + IS_ENABLED(CONFIG_DRM_XE_DEVMEM_MIRROR),
> + .check_pages_threshold = IS_DGFX(vm->xe) &&
> + IS_ENABLED(CONFIG_DRM_XE_DEVMEM_MIRROR) ?
> SZ_64K : 0,
> + };
> struct xe_svm_range *range;
> struct drm_gpusvm_range *r;
> struct drm_exec exec;
> @@ -631,9 +698,31 @@ int xe_svm_handle_pagefault(struct xe_vm *vm,
> struct xe_vma *vma,
> if (xe_svm_range_is_valid(range, tile))
> return 0;
>
> + /* 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;
> +
> + 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;
> + }
> + }
> +
> err = drm_gpusvm_range_get_pages(&vm->svm.gpusvm, r, &ctx);
> - if (err == -EFAULT || err == -EPERM) /* Corner where CPU
> mappings have changed */
> + /* Corner where CPU mappings have changed */
> + if (err == -EOPNOTSUPP || err == -EFAULT || err == -EPERM) {
> + if (err == -EOPNOTSUPP)
> + 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));
> goto retry;
> + }
> if (err)
> goto err_out;
>
> diff --git a/drivers/gpu/drm/xe/xe_svm.h
> b/drivers/gpu/drm/xe/xe_svm.h
> index 49c35e9ec183..5d4eeb2d34ce 100644
> --- a/drivers/gpu/drm/xe/xe_svm.h
> +++ b/drivers/gpu/drm/xe/xe_svm.h
> @@ -35,6 +35,11 @@ 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;
> };
>
> #if IS_ENABLED(CONFIG_DRM_GPUSVM)
