[PATCH 1/3] drm/xe: don't allocate fake mmap offsets for imported dma-bufs

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

ttm_bo_init_reserved() allocates a fake mmap offset (drm_vma_offset
node) for ttm_bo_type_sg BOs, even though xe rejects CPU faults on
imported dma-bufs. Since the offset space is limited to 1 TiB per
device on 64-bit, heavy P2P dma-buf importing on multi-GPU systems can
exhaust it and cause imports to fail with -ENOSPC.

Remove the vma_node once an imported BO is created and reject BOs
without one in xe_gem_mmap_offset_ioctl().

Fixes: dd08ebf6c352 ("drm/xe: Introduce a new DRM driver for Intel GPUs")
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
---
 drivers/gpu/drm/xe/xe_bo.c      | 6 ++++++
 drivers/gpu/drm/xe/xe_dma_buf.c | 9 +++++++++
 2 files changed, 15 insertions(+)

diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
index 42a6aa1a2e4a..0181f73ef66d 100644
--- a/drivers/gpu/drm/xe/xe_bo.c
+++ b/drivers/gpu/drm/xe/xe_bo.c
@@ -3851,6 +3851,12 @@ int xe_gem_mmap_offset_ioctl(struct drm_device *dev, void *data,
 	if (XE_IOCTL_DBG(xe, !gem_obj))
 		return -ENOENT;
 
+	/* Imported dma-bufs have no mmap offset since CPU access is rejected. */
+	if (XE_IOCTL_DBG(xe, !drm_vma_node_size(&gem_obj->vma_node))) {
+		xe_bo_put(gem_to_xe_bo(gem_obj));
+		return -EINVAL;
+	}
+
 	/* The mmap offset was set up at BO allocation time. */
 	args->offset = drm_vma_node_offset_addr(&gem_obj->vma_node);
 
diff --git a/drivers/gpu/drm/xe/xe_dma_buf.c b/drivers/gpu/drm/xe/xe_dma_buf.c
index 5bf13dc4b61d..17a8663a68de 100644
--- a/drivers/gpu/drm/xe/xe_dma_buf.c
+++ b/drivers/gpu/drm/xe/xe_dma_buf.c
@@ -12,6 +12,7 @@
 
 #include <drm/drm_device.h>
 #include <drm/drm_prime.h>
+#include <drm/drm_vma_manager.h>
 #include <drm/ttm/ttm_tt.h>
 
 #include "tests/xe_test.h"
@@ -353,6 +354,14 @@ xe_dma_buf_create_obj(struct drm_device *dev, struct dma_buf *dma_buf)
 	}
 	drm_gem_object_put(dummy_obj);
 
+	/*
+	 * CPU faults on imported BOs are rejected, so there is no point in
+	 * consuming fake mmap offset space for them.
+	 */
+	if (!ret)
+		drm_vma_offset_remove(bo->ttm.bdev->vma_manager,
+				      &bo->ttm.base.vma_node);
+
 	return ret ? ERR_PTR(ret) : &bo->ttm.base;
 }
 

-- 
2.56.0