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

Yadav, Sanjay Kumar
2026-04-20T12:20:45Z

On 16-04-2026 21:52, Matthew Auld wrote:
> 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.
Thanks Maarten for the review Ack, Matt A for the discussion.
>
>>
>>>   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;
>>
>