We use the global device inode, shared amongst all files, and not the
user's device filp to provide the backing storage for the mmap. The
vma->vm_file provides a redundant reference that breaks existing
expected behaviour that closing the user's device fd will release the
resources bound to it, if a mmap persists. (Even without the
vma->vm_file, the mmap will persist past the user's fd as the storage is
bound to the device, i.e. our reference is on the object not file.)
Fixes: cc662126b413 ("drm/i915: Introduce DRM_I915_GEM_MMAP_OFFSET")
Closes: https://gitlab.freedesktop.org/drm/intel/issues/919
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
---
drivers/gpu/drm/i915/gem/i915_gem_mman.c | 59 ++++++++++++++++++++++++
drivers/gpu/drm/i915/i915_drv.h | 10 ++++
2 files changed, 69 insertions(+)
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_mman.c b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
index 905527ce2999..ed0d9a2f0e7b 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_mman.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
@@ -4,6 +4,7 @@
* Copyright © 2014-2016 Intel Corporation
*/
+#include <linux/anon_inodes.h>
#include <linux/mman.h>
#include <linux/pfn_t.h>
#include <linux/sizes.h>
@@ -686,6 +687,46 @@ static const struct vm_operations_struct vm_ops_cpu = {
.close = vm_close,
};
+static int singleton_release(struct inode *inode, struct file *file)
+{
+ struct drm_i915_private *i915 = file->private_data;
+
+ cmpxchg(&i915->gem.mmap_singleton, file, NULL);
+ drm_dev_put(&i915->drm);
+
+ return 0;
+}
+
+static const struct file_operations singleton_fops = {
+ .owner = THIS_MODULE,
+ .release = singleton_release,
+};
+
+static struct file *mmap_singleton(struct drm_i915_private *i915)
+{
+ struct file *file;
+
+ rcu_read_lock();
+ file = i915->gem.mmap_singleton;
+ if (file && !get_file_rcu(file))
+ file = NULL;
+ rcu_read_unlock();
+ if (file)
+ return file;
+
+ file = anon_inode_getfile("i915.gem", &singleton_fops, i915, O_RDWR);
+ if (IS_ERR(file))
+ return file;
+
+ /* Everyone shares a single global address space */
+ file->f_mapping = i915->drm.anon_inode->i_mapping;
+
+ smp_store_mb(i915->gem.mmap_singleton, file);
+ drm_dev_get(&i915->drm);
+
+ return file;
+}
+
/*
* This overcomes the limitation in drm_gem_mmap's assignment of a
* drm_gem_object as the vma->vm_private_data. Since we need to
@@ -699,6 +740,7 @@ int i915_gem_mmap(struct file *filp, struct vm_area_struct *vma)
struct drm_device *dev = priv->minor->dev;
struct i915_mmap_offset *mmo = NULL;
struct drm_gem_object *obj = NULL;
+ struct file *anon;
if (drm_dev_is_unplugged(dev))
return -ENODEV;
@@ -747,9 +789,26 @@ int i915_gem_mmap(struct file *filp, struct vm_area_struct *vma)
vma->vm_flags &= ~VM_MAYWRITE;
}
+ anon = mmap_singleton(to_i915(obj->dev));
+ if (IS_ERR(anon)) {
+ drm_gem_object_put_unlocked(obj);
+ return PTR_ERR(anon);
+ }
+
vma->vm_flags |= VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP;
vma->vm_private_data = mmo;
+ /*
+ * We keep the ref on mmo->obj, not vm_file, but we require
+ * vma->vm_file->f_mapping, see vma_link(), for later revocation.
+ * Our userspace is accustomed to having per-file resource cleanup
+ * (i.e. contexts, objects and requests) on their close(fd), which
+ * requires avoiding extraneous references to their filp, hence why
+ * we prefer to use an anonymous file for their mmaps.
+ */
+ fput(vma->vm_file);
+ vma->vm_file = anon;
+
switch (mmo->mmap_type) {
case I915_MMAP_TYPE_WC:
vma->vm_page_prot =
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 2c7e3020e766..2ee9f57d165d 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1252,6 +1252,16 @@ struct drm_i915_private {
struct llist_head free_list;
struct work_struct free_work;
} contexts;
+
+ /*
+ * We replace the local file with a global mappings as the
+ * backing storage for the mmap is on the device and not
+ * on the struct file, and we do not want to prolong the
+ * lifetime of the local fd. To minimise the number of
+ * anonymous inodes we create, we use a global singleton to
+ * share the global mapping.
+ */
+ struct file *mmap_singleton;
} gem;
u8 pch_ssc_use;
--
2.25.0.rc0
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