Re: [PATCH v2] drm/xe: Convert stolen memory over to ttm_range_manager

[Matthew Auld <matthew.auld@intel.com>]

On 16/04/2026 16:33, Maarten Lankhorst wrote:
> Hey,
> 
> Den 2026-04-16 kl. 17:19, skrev Sanjay Yadav:
>> Stolen memory requires physically contiguous allocations for display
>> scanout and compressed framebuffers. The stolen memory manager was
>> sharing the gpu_buddy allocator backend with the VRAM manager, but
>> buddy manages non-contiguous power-of-two blocks making it a poor fit.
>> Stolen memory also has fundamentally different allocation patterns:
>>
>> - Allocation sizes are not power-of-two. Since buddy rounds up to the
>>    next power-of-two block size, a ~17MB request can fail even with
>>    ~22MB free, because the free space is fragmented across non-fitting
>>    power-of-two blocks.
>> - Hardware restrictions prevent using the first 4K page of stolen for
>>    certain allocations (e.g., FBC). The display code sets fpfn=1 to
>>    enforce this, but when fpfn != 0, gpu_buddy enables
>>    GPU_BUDDY_RANGE_ALLOCATION mode which disables the try_harder
>>    coalescing path, further reducing allocation success.
>>
>> This combination caused FBC compressed framebuffer (CFB) allocation
>> failures on platforms like NVL/PTL. In case of NVL where stolen memory
>> is ~56MB and the initial plane framebuffer consumes ~34MB at probe time,
>> leaving ~22MB for subsequent allocations.
>>
>> Use ttm_range_man_init_nocheck() to set up a drm_mm-backed TTM resource
>> manager for stolen memory. This reuses the TTM core's ttm_range_manager
>> callbacks, avoiding duplicate implementations.
>>
>> Tested on NVL with a 4K DP display: stolen_mm shows a single ~22MB
>> contiguous free hole after initial plane framebuffer allocation, and
>> FBC successfully allocates its CFB from that region. The corresponding
>> IGT was previously skipped and now passes.
>>
>> v2:
>> - Clarify that stolen memory requires contiguous allocations (Matt B)
>> - Properly handle xe_ttm_resource_visible() for stolen instead of
>>    unconditionally returning true (Matt A)
>>
>> Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/work_items/7631
>> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
>> Cc: Matthew Brost <matthew.brost@intel.com>
>> Suggested-by: Matthew Auld <matthew.auld@intel.com>
>> Assisted-by: GitHub Copilot:claude-sonnet-4.6
>> Signed-off-by: Sanjay Yadav <sanjay.kumar.yadav@intel.com>
>> ---
> Acked-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> 
> The changes look good, I never considered the differences between the
> buddy allocator and range manager. Glad to see this works a lot better!
> 
> One thing I did notice that in most cases, is there any reason for the
> range manager to use pages? It should be able to use bytes and remove
> a lot of shifts to convert between bytes and pages in the code.

Ah, that reminds me of: dfd1d2f7eb39 ("drm/xe/fbdev: Fix BIOS FB vs. 
stolen size check")

That would need to be converted back to pages, I think.

> 
>>   drivers/gpu/drm/xe/xe_bo.c             | 16 +++++--
>>   drivers/gpu/drm/xe/xe_device_types.h   |  3 ++
>>   drivers/gpu/drm/xe/xe_res_cursor.h     | 14 +++++-
>>   drivers/gpu/drm/xe/xe_ttm_stolen_mgr.c | 64 +++++++++-----------------
>>   drivers/gpu/drm/xe/xe_ttm_stolen_mgr.h |  9 ++++
>>   drivers/gpu/drm/xe/xe_ttm_vram_mgr.c   | 11 ++---
>>   6 files changed, 63 insertions(+), 54 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
>> index a7c2dc7f224c..b737edf04d60 100644
>> --- a/drivers/gpu/drm/xe/xe_bo.c
>> +++ b/drivers/gpu/drm/xe/xe_bo.c
>> @@ -599,11 +599,17 @@ static void xe_ttm_tt_destroy(struct ttm_device *ttm_dev, struct ttm_tt *tt)
>>   	kfree(tt);
>>   }
>>   
>> -static bool xe_ttm_resource_visible(struct ttm_resource *mem)
>> +static bool xe_ttm_resource_visible(struct xe_device *xe, struct ttm_resource *mem)
>>   {
>> -	struct xe_ttm_vram_mgr_resource *vres =
>> -		to_xe_ttm_vram_mgr_resource(mem);
>> +	struct xe_ttm_vram_mgr_resource *vres;
>>   
>> +	if (mem->mem_type == XE_PL_STOLEN) {
>> +		struct xe_ttm_stolen_mgr *mgr = xe->mem.stolen_mgr;
>> +
>> +		return mgr->io_base && !xe_ttm_stolen_cpu_access_needs_ggtt(xe);
>> +	}
>> +
>> +	vres = to_xe_ttm_vram_mgr_resource(mem);
>>   	return vres->used_visible_size == mem->size;
>>   }
>>   
>> @@ -621,7 +627,7 @@ bool xe_bo_is_visible_vram(struct xe_bo *bo)
>>   	if (drm_WARN_ON(bo->ttm.base.dev, !xe_bo_is_vram(bo)))
>>   		return false;
>>   
>> -	return xe_ttm_resource_visible(bo->ttm.resource);
>> +	return xe_ttm_resource_visible(xe_bo_device(bo), bo->ttm.resource);
>>   }
>>   
>>   static int xe_ttm_io_mem_reserve(struct ttm_device *bdev,
>> @@ -637,7 +643,7 @@ static int xe_ttm_io_mem_reserve(struct ttm_device *bdev,
>>   	case XE_PL_VRAM1: {
>>   		struct xe_vram_region *vram = res_to_mem_region(mem);
>>   
>> -		if (!xe_ttm_resource_visible(mem))
>> +		if (!xe_ttm_resource_visible(xe, mem))
>>   			return -EINVAL;
>>   
>>   		mem->bus.offset = mem->start << PAGE_SHIFT;
>> diff --git a/drivers/gpu/drm/xe/xe_device_types.h b/drivers/gpu/drm/xe/xe_device_types.h
>> index 150c76b2acaf..ffb84659c413 100644
>> --- a/drivers/gpu/drm/xe/xe_device_types.h
>> +++ b/drivers/gpu/drm/xe/xe_device_types.h
>> @@ -42,6 +42,7 @@ struct xe_ggtt;
>>   struct xe_i2c;
>>   struct xe_pat_ops;
>>   struct xe_pxp;
>> +struct xe_ttm_stolen_mgr;
>>   struct xe_vram_region;
>>   
>>   /**
>> @@ -278,6 +279,8 @@ struct xe_device {
>>   		struct ttm_resource_manager sys_mgr;
>>   		/** @mem.sys_mgr: system memory shrinker. */
>>   		struct xe_shrinker *shrinker;
>> +		/** @mem.stolen_mgr: stolen memory manager. */
>> +		struct xe_ttm_stolen_mgr *stolen_mgr;
>>   	} mem;
>>   
>>   	/** @sriov: device level virtualization data */
>> diff --git a/drivers/gpu/drm/xe/xe_res_cursor.h b/drivers/gpu/drm/xe/xe_res_cursor.h
>> index 5f4ab08c0686..0522caafd89d 100644
>> --- a/drivers/gpu/drm/xe/xe_res_cursor.h
>> +++ b/drivers/gpu/drm/xe/xe_res_cursor.h
>> @@ -101,7 +101,15 @@ static inline void xe_res_first(struct ttm_resource *res,
>>   	cur->mem_type = res->mem_type;
>>   
>>   	switch (cur->mem_type) {
>> -	case XE_PL_STOLEN:
>> +	case XE_PL_STOLEN: {
>> +		/* res->start is in pages (ttm_range_manager). */
>> +		cur->start = (res->start << PAGE_SHIFT) + start;
>> +		cur->size = size;
>> +		cur->remaining = size;
>> +		cur->node = NULL;
>> +		cur->mm = NULL;
>> +		break;
>> +	}
>>   	case XE_PL_VRAM0:
>>   	case XE_PL_VRAM1: {
>>   		struct gpu_buddy_block *block;
>> @@ -289,6 +297,10 @@ static inline void xe_res_next(struct xe_res_cursor *cur, u64 size)
>>   
>>   	switch (cur->mem_type) {
>>   	case XE_PL_STOLEN:
>> +		/* Just advance within the contiguous region. */
>> +		cur->start += size;
>> +		cur->size = cur->remaining;
>> +		break;
>>   	case XE_PL_VRAM0:
>>   	case XE_PL_VRAM1:
>>   		start = size - cur->size;
>> diff --git a/drivers/gpu/drm/xe/xe_ttm_stolen_mgr.c b/drivers/gpu/drm/xe/xe_ttm_stolen_mgr.c
>> index 27c9d72222cf..5e9070739e65 100644
>> --- a/drivers/gpu/drm/xe/xe_ttm_stolen_mgr.c
>> +++ b/drivers/gpu/drm/xe/xe_ttm_stolen_mgr.c
>> @@ -19,30 +19,11 @@
>>   #include "xe_device.h"
>>   #include "xe_gt_printk.h"
>>   #include "xe_mmio.h"
>> -#include "xe_res_cursor.h"
>>   #include "xe_sriov.h"
>>   #include "xe_ttm_stolen_mgr.h"
>> -#include "xe_ttm_vram_mgr.h"
>>   #include "xe_vram.h"
>>   #include "xe_wa.h"
>>   
>> -struct xe_ttm_stolen_mgr {
>> -	struct xe_ttm_vram_mgr base;
>> -
>> -	/* PCI base offset */
>> -	resource_size_t io_base;
>> -	/* GPU base offset */
>> -	resource_size_t stolen_base;
>> -
>> -	void __iomem *mapping;
>> -};
>> -
>> -static inline struct xe_ttm_stolen_mgr *
>> -to_stolen_mgr(struct ttm_resource_manager *man)
>> -{
>> -	return container_of(man, struct xe_ttm_stolen_mgr, base.manager);
>> -}
>> -
>>   /**
>>    * xe_ttm_stolen_cpu_access_needs_ggtt() - If we can't directly CPU access
>>    * stolen, can we then fallback to mapping through the GGTT.
>> @@ -210,12 +191,19 @@ static u64 detect_stolen(struct xe_device *xe, struct xe_ttm_stolen_mgr *mgr)
>>   #endif
>>   }
>>   
>> +static void xe_ttm_stolen_mgr_fini(struct drm_device *dev, void *arg)
>> +{
>> +	struct xe_device *xe = to_xe_device(dev);
>> +
>> +	ttm_range_man_fini_nocheck(&xe->ttm, XE_PL_STOLEN);
>> +}
>> +
>>   int xe_ttm_stolen_mgr_init(struct xe_device *xe)
>>   {
>>   	struct pci_dev *pdev = to_pci_dev(xe->drm.dev);
>>   	struct xe_ttm_stolen_mgr *mgr;
>>   	u64 stolen_size, io_size;
>> -	int err;
>> +	int ret;
>>   
>>   	mgr = drmm_kzalloc(&xe->drm, sizeof(*mgr), GFP_KERNEL);
>>   	if (!mgr)
>> @@ -244,12 +232,12 @@ int xe_ttm_stolen_mgr_init(struct xe_device *xe)
>>   	if (mgr->io_base && !xe_ttm_stolen_cpu_access_needs_ggtt(xe))
>>   		io_size = stolen_size;
>>   
>> -	err = __xe_ttm_vram_mgr_init(xe, &mgr->base, XE_PL_STOLEN, stolen_size,
>> -				     io_size, PAGE_SIZE);
>> -	if (err) {
>> -		drm_dbg_kms(&xe->drm, "Stolen mgr init failed: %i\n", err);
>> -		return err;
>> -	}
>> +	ret = ttm_range_man_init_nocheck(&xe->ttm, XE_PL_STOLEN, false,
>> +					 stolen_size >> PAGE_SHIFT);
>> +	if (ret)
>> +		return ret;
>> +
>> +	xe->mem.stolen_mgr = mgr;
>>   
>>   	drm_dbg_kms(&xe->drm, "Initialized stolen memory support with %llu bytes\n",
>>   		    stolen_size);
>> @@ -257,36 +245,32 @@ int xe_ttm_stolen_mgr_init(struct xe_device *xe)
>>   	if (io_size)
>>   		mgr->mapping = devm_ioremap_wc(&pdev->dev, mgr->io_base, io_size);
>>   
>> -	return 0;
>> +	return drmm_add_action_or_reset(&xe->drm, xe_ttm_stolen_mgr_fini, mgr);
>>   }
>>   
>>   u64 xe_ttm_stolen_io_offset(struct xe_bo *bo, u32 offset)
>>   {
>>   	struct xe_device *xe = xe_bo_device(bo);
>> -	struct ttm_resource_manager *ttm_mgr = ttm_manager_type(&xe->ttm, XE_PL_STOLEN);
>> -	struct xe_ttm_stolen_mgr *mgr = to_stolen_mgr(ttm_mgr);
>> -	struct xe_res_cursor cur;
>> +	struct xe_ttm_stolen_mgr *mgr = xe->mem.stolen_mgr;
>>   
>>   	XE_WARN_ON(!mgr->io_base);
>>   
>>   	if (xe_ttm_stolen_cpu_access_needs_ggtt(xe))
>>   		return mgr->io_base + xe_bo_ggtt_addr(bo) + offset;
>>   
>> -	xe_res_first(bo->ttm.resource, offset, 4096, &cur);
>> -	return mgr->io_base + cur.start;
>> +	/* Range allocator: res->start is in pages. */
>> +	return mgr->io_base + (bo->ttm.resource->start << PAGE_SHIFT) + offset;
>>   }
>>   
>>   static int __xe_ttm_stolen_io_mem_reserve_bar2(struct xe_device *xe,
>>   					       struct xe_ttm_stolen_mgr *mgr,
>>   					       struct ttm_resource *mem)
>>   {
>> -	struct xe_res_cursor cur;
>> -
>>   	if (!mgr->io_base)
>>   		return -EIO;
>>   
>> -	xe_res_first(mem, 0, 4096, &cur);
>> -	mem->bus.offset = cur.start;
>> +	/* Range allocator always produces contiguous allocations. */
>> +	mem->bus.offset = mem->start << PAGE_SHIFT;
>>   
>>   	drm_WARN_ON(&xe->drm, !(mem->placement & TTM_PL_FLAG_CONTIGUOUS));
>>   
>> @@ -329,8 +313,7 @@ static int __xe_ttm_stolen_io_mem_reserve_stolen(struct xe_device *xe,
>>   
>>   int xe_ttm_stolen_io_mem_reserve(struct xe_device *xe, struct ttm_resource *mem)
>>   {
>> -	struct ttm_resource_manager *ttm_mgr = ttm_manager_type(&xe->ttm, XE_PL_STOLEN);
>> -	struct xe_ttm_stolen_mgr *mgr = ttm_mgr ? to_stolen_mgr(ttm_mgr) : NULL;
>> +	struct xe_ttm_stolen_mgr *mgr = xe->mem.stolen_mgr;
>>   
>>   	if (!mgr || !mgr->io_base)
>>   		return -EIO;
>> @@ -343,8 +326,5 @@ int xe_ttm_stolen_io_mem_reserve(struct xe_device *xe, struct ttm_resource *mem)
>>   
>>   u64 xe_ttm_stolen_gpu_offset(struct xe_device *xe)
>>   {
>> -	struct xe_ttm_stolen_mgr *mgr =
>> -		to_stolen_mgr(ttm_manager_type(&xe->ttm, XE_PL_STOLEN));
>> -
>> -	return mgr->stolen_base;
>> +	return xe->mem.stolen_mgr->stolen_base;
>>   }
>> diff --git a/drivers/gpu/drm/xe/xe_ttm_stolen_mgr.h b/drivers/gpu/drm/xe/xe_ttm_stolen_mgr.h
>> index 8e877d1e839b..049e91e77326 100644
>> --- a/drivers/gpu/drm/xe/xe_ttm_stolen_mgr.h
>> +++ b/drivers/gpu/drm/xe/xe_ttm_stolen_mgr.h
>> @@ -12,6 +12,15 @@ struct ttm_resource;
>>   struct xe_bo;
>>   struct xe_device;
>>   
>> +struct xe_ttm_stolen_mgr {
>> +	/* PCI base offset */
>> +	resource_size_t io_base;
>> +	/* GPU base offset */
>> +	resource_size_t stolen_base;
>> +
>> +	void __iomem *mapping;
>> +};
>> +
>>   int xe_ttm_stolen_mgr_init(struct xe_device *xe);
>>   int xe_ttm_stolen_io_mem_reserve(struct xe_device *xe, struct ttm_resource *mem);
>>   bool xe_ttm_stolen_cpu_access_needs_ggtt(struct xe_device *xe);
>> diff --git a/drivers/gpu/drm/xe/xe_ttm_vram_mgr.c b/drivers/gpu/drm/xe/xe_ttm_vram_mgr.c
>> index 5fd0d5506a7e..79ef8e1b5e5c 100644
>> --- a/drivers/gpu/drm/xe/xe_ttm_vram_mgr.c
>> +++ b/drivers/gpu/drm/xe/xe_ttm_vram_mgr.c
>> @@ -301,14 +301,13 @@ int __xe_ttm_vram_mgr_init(struct xe_device *xe, struct xe_ttm_vram_mgr *mgr,
>>   			   u64 default_page_size)
>>   {
>>   	struct ttm_resource_manager *man = &mgr->manager;
>> +	const char *name;
>>   	int err;
>>   
>> -	if (mem_type != XE_PL_STOLEN) {
>> -		const char *name = mem_type == XE_PL_VRAM0 ? "vram0" : "vram1";
>> -		man->cg = drmm_cgroup_register_region(&xe->drm, name, size);
>> -		if (IS_ERR(man->cg))
>> -			return PTR_ERR(man->cg);
>> -	}
>> +	name = mem_type == XE_PL_VRAM0 ? "vram0" : "vram1";
>> +	man->cg = drmm_cgroup_register_region(&xe->drm, name, size);
>> +	if (IS_ERR(man->cg))
>> +		return PTR_ERR(man->cg);
>>   
>>   	man->func = &xe_ttm_vram_mgr_func;
>>   	mgr->mem_type = mem_type;
>