[PATCH v2] drm/gem: Fix mmap fake offset handling for drm_gem_object_funcs.mmap

[Gerd Hoffmann]

  Hi,

> > update-object-after-move works fine.
> > 
> > try zap mappings with madvise(dontneed) has no bad effects (after vram
> > move, trying to force re-creating the ptes).
> 
> Well if it's broken the zapping wouldn't work :-)
> 
> > didn't try the memory pressure thing yet.
> 
> I'm surprised ... and I have no idea how/why it keeps working.
> 
> For my paranoia, can you instrument the ttm page fault handler, and double
> check that we get new faults after the move, and set up new ptes for the
> same old mapping, but now pointing at the new place in vram?

Hmm, only the drm device mapping is faulted in after moving it,
the dma-buf mapping is not.  Fixed by:

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>From 3a7f6c6dbf3b1e4b412c2b283b2ea4edff9f33b5 Mon Sep 17 00:00:00 2001
From: Gerd Hoffmann <kraxel at redhat.com>
Date: Thu, 21 Nov 2019 08:39:17 +0100
Subject: [PATCH] drm: share address space for dma bufs

---
 drivers/gpu/drm/drm_prime.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 0814211b0f3f..07c88d2aedee 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -240,6 +240,7 @@ void drm_prime_destroy_file_private(struct drm_prime_file_private *prime_fpriv)
 struct dma_buf *drm_gem_dmabuf_export(struct drm_device *dev,
 				      struct dma_buf_export_info *exp_info)
 {
+	struct drm_gem_object *obj = exp_info->priv;
 	struct dma_buf *dma_buf;
 
 	dma_buf = dma_buf_export(exp_info);
@@ -247,7 +248,8 @@ struct dma_buf *drm_gem_dmabuf_export(struct drm_device *dev,
 		return dma_buf;
 
 	drm_dev_get(dev);
-	drm_gem_object_get(exp_info->priv);
+	drm_gem_object_get(obj);
+	dma_buf->file->f_mapping = obj->dev->anon_inode->i_mapping;
 
 	return dma_buf;
 }
-- 
2.18.1

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git branch: https://git.kraxel.org/cgit/linux/log/?h=drm-mmap-debug

cheers,
  Gerd