On Wed, 2025-02-12 at 18:11 -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) > > Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx> > --- > drivers/gpu/drm/xe/xe_svm.c | 111 > ++++++++++++++++++++++++++++++++++-- > drivers/gpu/drm/xe/xe_svm.h | 5 ++ > 2 files changed, 112 insertions(+), 4 deletions(-) > > diff --git a/drivers/gpu/drm/xe/xe_svm.c > b/drivers/gpu/drm/xe/xe_svm.c > index 0a78a838508c..2e1e0f31c1a8 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; > @@ -512,7 +517,6 @@ 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, > @@ -592,6 +596,71 @@ 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 struct xe_bo *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 ERR_PTR(-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)); The way this is done now looks good, although the corresponding multi- device commit https://gitlab.freedesktop.org/thomash/kernel/-/commit/1f204b5d05896e5cf63ab54a679ee343e76600ff Goes one step further and removes the bo return of this function to favor an int error code. The caller doesn't really use the bo, right? > + > + blocks = &to_xe_ttm_vram_mgr_resource(bo->ttm.resource)- > >blocks; > + list_for_each_entry(block, blocks, link) > + block->private = vr; > + > + /* > + * Take ref because as soon as drm_gpusvm_migrate_to_devmem > succeeds the > + * creation ref can be dropped upon CPU fault or unmap. > + */ > + xe_bo_get(bo); > + > + 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); /* Local ref */ > + xe_bo_put(bo); /* Creation ref */ Strictly, with the drm_gpusvm_devmem_init() succeeding, this bo put should be an xe_svm_devmem_release(), right? While equivalent here, if devmem_init moving forward sets up other resources that are expected to be released at devmem_release time, they'd be leaked. > + bo = ERR_PTR(err); > + } > + > +unlock: > + mmap_read_unlock(mm); > + mmput(mm); > + > + return bo; > +} > + > /** > * xe_svm_handle_pagefault() - SVM handle page fault > * @vm: The VM. > @@ -600,7 +669,8 @@ 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. > */ > @@ -608,11 +678,18 @@ 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; > struct dma_fence *fence; > + struct xe_bo *bo = NULL; > ktime_t end = 0; > int err; > > @@ -620,6 +697,9 @@ int xe_svm_handle_pagefault(struct xe_vm *vm, > struct xe_vma *vma, > xe_assert(vm->xe, xe_vma_is_cpu_addr_mirror(vma)); > > retry: > + xe_bo_put(bo); > + bo = NULL; > + > /* Always process UNMAPs first so view SVM ranges is current > */ > err = xe_svm_garbage_collector(vm); > if (err) > @@ -635,9 +715,31 @@ 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->migrated && range->base.flags.migrate_devmem && > + xe_svm_range_size(range) >= SZ_64K) { > + range->migrated = true; > + > + bo = xe_svm_alloc_vram(vm, tile, range, &ctx); > + if (IS_ERR(bo)) { > + drm_info(&vm->xe->drm, > + "VRAM allocation failed, falling > back to retrying, asid=%u, errno %pe\n", > + vm->usm.asid, bo); Typically we use drm_dbg() to print error messages to avoid spamming the logs and facilitate dynamic debug. Should we change this. /Thomas > + bo = NULL; > + 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_info(&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; > > @@ -668,6 +770,7 @@ int xe_svm_handle_pagefault(struct xe_vm *vm, > struct xe_vma *vma, > dma_fence_put(fence); > > err_out: > + xe_bo_put(bo); > > return err; > } > diff --git a/drivers/gpu/drm/xe/xe_svm.h > b/drivers/gpu/drm/xe/xe_svm.h > index 0fa525d34987..984a61651d9e 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; > + /** > + * @migrated: Range has been migrated to device memory, > protected by > + * GPU fault handler locking. > + */ > + u8 migrated :1; > }; > > int xe_devm_add(struct xe_tile *tile, struct xe_vram_region *vr);
