Multiplane dmabuf import mmap offset computation

mmap fails on some platforms when trying to map
a dmabuf with a non-zero offset.

Instead of passing in the offset to map to, get the
base address and add the offset afterwards.

BUG: none
TEST=./ozone_gl_unittests --gtest_filter=GLImageNativePixmap/GLImageBindTest/5.BindTexImage --gtest_also_run_disabled_tests

Change-Id: Ie20e460e4099f937452a96a6e64b39ec56f1cc3a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1979096
Auto-Submit: Fritz Koenig <frkoenig@chromium.org>
Reviewed-by: Daniele Castagna <dcastagna@chromium.org>
Commit-Queue: Fritz Koenig <frkoenig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#731605}

ui/gfx/linux/client_native_pixmap_dmabuf.cc

@@ -83,7 +83,7 @@ ClientNativePixmapDmaBuf::PlaneInfo::PlaneInfo(PlaneInfo&& info)
 
 ClientNativePixmapDmaBuf::PlaneInfo::~PlaneInfo() {
   if (data) {
-    int ret = munmap(data, size);
+    int ret = munmap(data, offset + size);
     DCHECK(!ret);
   }
 }
@@ -183,7 +183,6 @@ ClientNativePixmapDmaBuf::ImportFromDmabuf(gfx::NativePixmapHandle handle,
     return nullptr;
   }
 
-  const size_t page_size = base::GetPageSize();
   for (size_t i = 0; i < handle.planes.size(); ++i) {
     // Verify that the plane buffer has appropriate size.
     size_t min_stride = 0;
@@ -201,22 +200,19 @@ ClientNativePixmapDmaBuf::ImportFromDmabuf(gfx::NativePixmapHandle handle,
     if (!min_size.IsValid() || handle.planes[i].size < min_size.ValueOrDie())
       return nullptr;
 
-    // mmap() fails if the offset argument is not page-aligned.
-    // Since handle.planes[i].offset is possibly not page-aligned, we
-    // have to map with an additional offset to be aligned to the page.
-    const size_t extra_offset = handle.planes[i].offset % page_size;
-    size_t map_size =
-        base::checked_cast<size_t>(handle.planes[i].size + extra_offset);
-    plane_info[i].offset = extra_offset;
+    const size_t map_size = base::checked_cast<size_t>(handle.planes[i].size);
+    plane_info[i].offset = handle.planes[i].offset;
     plane_info[i].size = map_size;
 
-    void* data =
-        mmap(nullptr, map_size, (PROT_READ | PROT_WRITE), MAP_SHARED,
-             handle.planes[i].fd.get(), handle.planes[i].offset - extra_offset);
+    void* data = mmap(nullptr, map_size + handle.planes[i].offset,
+                      (PROT_READ | PROT_WRITE), MAP_SHARED,
+                      handle.planes[i].fd.get(), 0);
+
     if (data == MAP_FAILED) {
       logging::SystemErrorCode mmap_error = logging::GetLastSystemErrorCode();
       if (mmap_error == ENOMEM)
-        base::TerminateBecauseOutOfMemory(map_size);
+        base::TerminateBecauseOutOfMemory(map_size +
+                                          handle.planes[i].offset);
       LOG(ERROR) << "Failed to mmap dmabuf: "
                  << logging::SystemErrorCodeToString(mmap_error);
       return nullptr;