drm/i915/gem: Fix Virtual Memory mapping boundaries calculation

commit 8bdd9ef upstream.

Calculating the size of the mapped area as the lesser value
between the requested size and the actual size does not consider
the partial mapping offset. This can cause page fault access.

Fix the calculation of the starting and ending addresses, the
total size is now deduced from the difference between the end and
start addresses.

Additionally, the calculations have been rewritten in a clearer
and more understandable form.

Fixes: c58305a ("drm/i915: Use remap_io_mapping() to prefault all PTE in a single pass")
Reported-by: Jann Horn <jannh@google.com>
Co-developed-by: Chris Wilson <chris.p.wilson@linux.intel.com>
Signed-off-by: Chris Wilson <chris.p.wilson@linux.intel.com>
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: <stable@vger.kernel.org> # v4.9+
Reviewed-by: Jann Horn <jannh@google.com>
Reviewed-by: Jonathan Cavitt <Jonathan.cavitt@intel.com>
[Joonas: Add Requires: tag]
Requires: 60a2066 ("drm/i915/gem: Adjust vma offset for framebuffer mmap offset")
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240802083850.103694-3-andi.shyti@linux.intel.com
(cherry picked from commit 97b6784)
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/gpu/drm/i915/i915_gem.c

@@ -2009,6 +2009,39 @@ compute_partial_view(struct drm_i915_gem_object *obj,
  return view;
 }
 
+static void set_address_limits(struct vm_area_struct *area,
+ struct i915_vma *vma,
+ unsigned long *start_vaddr,
+ unsigned long *end_vaddr)
+{
+ unsigned long vm_start, vm_end, vma_size; /* user's memory parameters */
+ long start, end; /* memory boundaries */
+
+ /*
+ * Let's move into the ">> PAGE_SHIFT"
+ * domain to be sure not to lose bits
+ */
+ vm_start = area->vm_start >> PAGE_SHIFT;
+ vm_end = area->vm_end >> PAGE_SHIFT;
+ vma_size = vma->size >> PAGE_SHIFT;
+
+ /*
+ * Calculate the memory boundaries by considering the offset
+ * provided by the user during memory mapping and the offset
+ * provided for the partial mapping.
+ */
+ start = vm_start;
+ start += vma->ggtt_view.partial.offset;
+ end = start + vma_size;
+
+ start = max_t(long, start, vm_start);
+ end = min_t(long, end, vm_end);
+
+ /* Let's move back into the "<< PAGE_SHIFT" domain */
+ *start_vaddr = (unsigned long)start << PAGE_SHIFT;
+ *end_vaddr = (unsigned long)end << PAGE_SHIFT;
+}
+
 /**
  * i915_gem_fault - fault a page into the GTT
  * @vmf: fault info
@@ -2036,8 +2069,10 @@ vm_fault_t i915_gem_fault(struct vm_fault *vmf)
  struct drm_i915_private *dev_priv = to_i915(dev);
  struct i915_ggtt *ggtt = &dev_priv->ggtt;
  bool write = !!(vmf->flags & FAULT_FLAG_WRITE);
+ unsigned long start, end; /* memory boundaries */
  struct i915_vma *vma;
  pgoff_t page_offset;
+ unsigned long pfn;
  int ret;
 
  /* Sanity check that we allow writing into this object */
@@ -2119,12 +2154,14 @@ vm_fault_t i915_gem_fault(struct vm_fault *vmf)
  if (ret)
  goto err_unpin;
 
+ set_address_limits(area, vma, &start, &end);
+
+ pfn = (ggtt->gmadr.start + i915_ggtt_offset(vma)) >> PAGE_SHIFT;
+ pfn += (start - area->vm_start) >> PAGE_SHIFT;
+ pfn -= vma->ggtt_view.partial.offset;
+
  /* Finally, remap it using the new GTT offset */
- ret = remap_io_mapping(area,
- area->vm_start + (vma->ggtt_view.partial.offset << PAGE_SHIFT),
- (ggtt->gmadr.start + vma->node.start) >> PAGE_SHIFT,
- min_t(u64, vma->size, area->vm_end - area->vm_start),
- &ggtt->iomap);
+ ret = remap_io_mapping(area, start, pfn, end - start, &ggtt->iomap);
  if (ret)
  goto err_fence;