drm/panfrost: Don't try to map pages that are already mapped

We allocate 2MB chunks at a time, so it might appear that a page fault
has already been handled by a previous page fault when we reach
panfrost_mmu_map_fault_addr(). Bail out in that case to avoid mapping the
same area twice.

Cc: <stable@vger.kernel.org>
Fixes: 187d2929 ("drm/panfrost: Add support for GPU heap allocations")
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210205111757.585248-3-boris.brezillon@collabora.com

drivers/gpu/drm/panfrost/panfrost_mmu.c

@@ -488,8 +488,14 @@ static int panfrost_mmu_map_fault_addr(struct panfrost_device *pfdev, int as,
 		}
 		bo->base.pages = pages;
 		bo->base.pages_use_count = 1;
-	} else
+	} else {
 		pages = bo->base.pages;
+		if (pages[page_offset]) {
+			/* Pages are already mapped, bail out. */
+			mutex_unlock(&bo->base.pages_lock);
+			goto out;
+		}
+	}
 
 	mapping = bo->base.base.filp->f_mapping;
 	mapping_set_unevictable(mapping);
@@ -522,6 +528,7 @@ static int panfrost_mmu_map_fault_addr(struct panfrost_device *pfdev, int as,
 
 	dev_dbg(pfdev->dev, "mapped page fault @ AS%d %llx", as, addr);
 
+out:
 	panfrost_gem_mapping_put(bomapping);
 
 	return 0;