[PATCH v3 2/3] drm/pagemap: Add a populate_mm op
Thomas Hellström
thomas.hellstrom at linux.intel.com
Fri Jun 13 14:02:18 UTC 2025
Add an operation to populate a part of a drm_mm with device
private memory. Clarify how migration using it is intended
to work.
v3:
- Kerneldoc fixes and updates (Matt Brost).
Signed-off-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>
Reviewed-by: Matthew Brost <matthew.brost at intel.com> #v1
---
drivers/gpu/drm/drm_gpusvm.c | 7 ++--
drivers/gpu/drm/drm_pagemap.c | 67 ++++++++++++++++++++++++++++-------
include/drm/drm_pagemap.h | 34 ++++++++++++++++++
3 files changed, 91 insertions(+), 17 deletions(-)
diff --git a/drivers/gpu/drm/drm_gpusvm.c b/drivers/gpu/drm/drm_gpusvm.c
index ef81381609de..51afc8a9704d 100644
--- a/drivers/gpu/drm/drm_gpusvm.c
+++ b/drivers/gpu/drm/drm_gpusvm.c
@@ -175,11 +175,8 @@
* }
*
* if (driver_migration_policy(range)) {
- * mmap_read_lock(mm);
- * devmem = driver_alloc_devmem();
- * err = drm_pagemap_migrate_to_devmem(devmem, gpusvm->mm, gpuva_start,
- * gpuva_end, driver_pgmap_owner());
- * mmap_read_unlock(mm);
+ * err = drm_pagemap_populate_mm(driver_choose_drm_pagemap(),
+ * gpuva_start, gpuva_end, gpusvm->mm);
* if (err) // CPU mappings may have changed
* goto retry;
* }
diff --git a/drivers/gpu/drm/drm_pagemap.c b/drivers/gpu/drm/drm_pagemap.c
index b7a0e6d15aff..e4120c8db262 100644
--- a/drivers/gpu/drm/drm_pagemap.c
+++ b/drivers/gpu/drm/drm_pagemap.c
@@ -6,6 +6,7 @@
#include <linux/dma-mapping.h>
#include <linux/migrate.h>
#include <linux/pagemap.h>
+#include <drm/drm_drv.h>
#include <drm/drm_pagemap.h>
/**
@@ -20,23 +21,30 @@
* system.
*
* Typically the DRM pagemap receives requests from one or more DRM GPU SVM
- * instances to populate struct mm_struct virtual ranges with memory.
+ * instances to populate struct mm_struct virtual ranges with memory, and the
+ * migration is best effort only and may thus fail. The implementation should
+ * also handle device unbinding by blocking (return an -ENODEV) error for new
+ * population requests and after that migrate all device pages to system ram.
*/
/**
* DOC: Migration
*
- * The migration support is quite simple, allowing migration between RAM and
- * device memory at the range granularity. For example, GPU SVM currently does
- * not support mixing RAM and device memory pages within a range. This means
- * that upon GPU fault, the entire range can be migrated to device memory, and
- * upon CPU fault, the entire range is migrated to RAM. Mixed RAM and device
- * memory storage within a range could be added in the future if required.
- *
- * The reasoning for only supporting range granularity is as follows: it
- * simplifies the implementation, and range sizes are driver-defined and should
- * be relatively small.
- *
+ * Migration granularity typically follows the GPU SVM range requests, but
+ * if there are clashes, due to races or due to the fact that multiple GPU
+ * SVM instances have different views of the ranges used, and because of that
+ * parts of a requested range is already present in the requested device memory,
+ * the implementation has a variety of options. It can fail and it can choose
+ * to populate only the part of the range that isn't already in device memory,
+ * and it can evict the range to system before trying to migrate. Ideally an
+ * implementation would just try to migrate the missing part of the range and
+ * allocate just enough memory to do so.
+ *
+ * When migrating to system memory as a response to a cpu fault or a device
+ * memory eviction request, currently a full device memory allocation is
+ * migrated back to system. Moving forward this might need improvement for
+ * situations where a single page needs bouncing between system memory and
+ * device memory due to, for example, atomic operations.
*
* Key DRM pagemap components:
*
@@ -786,3 +794,38 @@ struct drm_pagemap *drm_pagemap_page_to_dpagemap(struct page *page)
return zdd->devmem_allocation->dpagemap;
}
EXPORT_SYMBOL_GPL(drm_pagemap_page_to_dpagemap);
+
+/**
+ * drm_pagemap_populate_mm() - Populate a virtual range with device memory pages
+ * @dpagemap: Pointer to the drm_pagemap managing the device memory
+ * @start: Start of the virtual range to populate.
+ * @end: End of the virtual range to populate.
+ * @mm: Pointer to the virtual address space.
+ * @timeslice_ms: The time requested for the migrated pages to
+ * be present in the cpu memory map before migrated back.
+ *
+ * Attempt to populate a virtual range with device memory pages,
+ * clearing them or migrating data from the existing pages if necessary.
+ * The function is best effort only, and implementations may vary
+ * in how hard they try to satisfy the request.
+ *
+ * Return: %0 on success, negative error code on error. If the hardware
+ * device was removed / unbound the function will return %-ENODEV.
+ */
+int drm_pagemap_populate_mm(struct drm_pagemap *dpagemap,
+ unsigned long start, unsigned long end,
+ struct mm_struct *mm,
+ unsigned long timeslice_ms)
+{
+ int err;
+
+ if (!mmget_not_zero(mm))
+ return -EFAULT;
+ mmap_read_lock(mm);
+ err = dpagemap->ops->populate_mm(dpagemap, start, end, mm,
+ timeslice_ms);
+ mmap_read_unlock(mm);
+ mmput(mm);
+
+ return err;
+}
diff --git a/include/drm/drm_pagemap.h b/include/drm/drm_pagemap.h
index dabc9c365df4..e5f20a1235be 100644
--- a/include/drm/drm_pagemap.h
+++ b/include/drm/drm_pagemap.h
@@ -92,6 +92,35 @@ struct drm_pagemap_ops {
struct device *dev,
struct drm_pagemap_device_addr addr);
+ /**
+ * @populate_mm: Populate part of the mm with @dpagemap memory,
+ * migrating existing data.
+ * @dpagemap: The struct drm_pagemap managing the memory.
+ * @start: The virtual start address in @mm
+ * @end: The virtual end address in @mm
+ * @mm: Pointer to a live mm. The caller must have an mmget()
+ * reference.
+ *
+ * The caller will have the mm lock at least in read mode.
+ * Note that there is no guarantee that the memory is resident
+ * after the function returns, it's best effort only.
+ * When the mm is not using the memory anymore,
+ * it will be released. The struct drm_pagemap might have a
+ * mechanism in place to reclaim the memory and the data will
+ * then be migrated. Typically to system memory.
+ * The implementation should hold sufficient runtime power-
+ * references while pages are used in an address space and
+ * should ideally guard against hardware device unbind in
+ * a way such that device pages are migrated back to system
+ * followed by device page removal. The implementation should
+ * return -ENODEV after device removal.
+ *
+ * Return: 0 if successful. Negative error code on error.
+ */
+ int (*populate_mm)(struct drm_pagemap *dpagemap,
+ unsigned long start, unsigned long end,
+ struct mm_struct *mm,
+ unsigned long timeslice_ms);
};
/**
@@ -205,4 +234,9 @@ void drm_pagemap_devmem_init(struct drm_pagemap_devmem *devmem_allocation,
const struct drm_pagemap_devmem_ops *ops,
struct drm_pagemap *dpagemap, size_t size);
+int drm_pagemap_populate_mm(struct drm_pagemap *dpagemap,
+ unsigned long start, unsigned long end,
+ struct mm_struct *mm,
+ unsigned long timeslice_ms);
+
#endif
--
2.49.0
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