Commit 06208374 authored by Thomas Hellström's avatar Thomas Hellström
Browse files

drm/xe/svm: Serialize migration to device if racing 



Introduce an rw-semaphore to serialize migration to device if
it's likely that migration races with another device migration
of the same CPU address space range.
This is a temporary fix to attempt to mitigate a livelock that
might happen if many devices try to migrate a range at the same
time, and it affects only devices using the xe driver.
A longer term fix is probably improvements in the core mm
migration layer.

Suggested-by: default avatarMatthew Brost <matthew.brost@intel.com>
Signed-off-by: default avatarThomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: default avatarMatthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20251219113320.183860-25-thomas.hellstrom@linux.intel.com
parent ec265e1f

drivers/gpu/drm/xe/xe_svm.c

+20 −2
Original line number Diff line number Diff line
@@ -1593,10 +1593,12 @@ struct drm_pagemap *xe_vma_resolve_pagemap(struct xe_vma *vma, struct xe_tile *t 
int xe_svm_alloc_vram(struct xe_svm_range *range, const struct drm_gpusvm_ctx *ctx,

		      struct drm_pagemap *dpagemap)

{

	static DECLARE_RWSEM(driver_migrate_lock);

	struct xe_vm *vm = range_to_vm(&range->base);

	enum drm_gpusvm_scan_result migration_state;

	struct xe_device *xe = vm->xe;

	int err, retries = 1;

	bool write_locked = false;



	xe_assert(range_to_vm(&range->base)->xe, range->base.pages.flags.migrate_devmem);

	range_debug(range, "ALLOCATE VRAM");
@@ -1615,16 +1617,32 @@ int xe_svm_alloc_vram(struct xe_svm_range *range, const struct drm_gpusvm_ctx *c 
		drm_dbg(&xe->drm, "Request migration to device memory on \"%s\".\n",

			dpagemap->drm->unique);



	err = down_read_interruptible(&driver_migrate_lock);

	if (err)

		return err;

	do {

		err = drm_pagemap_populate_mm(dpagemap, xe_svm_range_start(range),

					      xe_svm_range_end(range),

					      range->base.gpusvm->mm,

					      ctx->timeslice_ms);



		if (err == -EBUSY && retries)

			drm_gpusvm_range_evict(range->base.gpusvm, &range->base);

		if (err == -EBUSY && retries) {

			if (!write_locked) {

				int lock_err;



				up_read(&driver_migrate_lock);

				lock_err = down_write_killable(&driver_migrate_lock);

				if (lock_err)

					return lock_err;

				write_locked = true;

			}

			drm_gpusvm_range_evict(range->base.gpusvm, &range->base);

		}

	} while (err == -EBUSY && retries--);

	if (write_locked)

		up_write(&driver_migrate_lock);

	else

		up_read(&driver_migrate_lock);



	return err;

}