drm/ttm: Remap all page faults to per process dummy page.

On device removal reroute all CPU mappings to dummy page.

v3:
Remove loop to find DRM file and instead access it
by vma->vm_file->private_data. Move dummy page installation
into a separate function.

v4:
Map the entire BOs VA space into on demand allocated dummy page
on the first fault for that BO.

v5: Remove duplicate return.

v6: Polish ttm_bo_vm_dummy_page, remove superfluous code.
Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210512142648.666476-2-andrey.grodzovsky@amd.com

drivers/gpu/drm/ttm/ttm_bo_vm.c

@@ -34,6 +34,8 @@
 #include <drm/ttm/ttm_bo_driver.h>
 #include <drm/ttm/ttm_placement.h>
 #include <drm/drm_vma_manager.h>
+#include <drm/drm_drv.h>
+#include <drm/drm_managed.h>
 #include <linux/mm.h>
 #include <linux/pfn_t.h>
 #include <linux/rbtree.h>
@@ -380,19 +382,69 @@ vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
 }
 EXPORT_SYMBOL(ttm_bo_vm_fault_reserved);
 
+static void ttm_bo_release_dummy_page(struct drm_device *dev, void *res)
+{
+	struct page *dummy_page = (struct page *)res;
+
+	__free_page(dummy_page);
+}
+
+vm_fault_t ttm_bo_vm_dummy_page(struct vm_fault *vmf, pgprot_t prot)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	struct ttm_buffer_object *bo = vma->vm_private_data;
+	struct drm_device *ddev = bo->base.dev;
+	vm_fault_t ret = VM_FAULT_NOPAGE;
+	unsigned long address;
+	unsigned long pfn;
+	struct page *page;
+
+	/* Allocate new dummy page to map all the VA range in this VMA to it*/
+	page = alloc_page(GFP_KERNEL | __GFP_ZERO);
+	if (!page)
+		return VM_FAULT_OOM;
+
+	/* Set the page to be freed using drmm release action */
+	if (drmm_add_action_or_reset(ddev, ttm_bo_release_dummy_page, page))
+		return VM_FAULT_OOM;
+
+	pfn = page_to_pfn(page);
+
+	/* Prefault the entire VMA range right away to avoid further faults */
+	for (address = vma->vm_start; address < vma->vm_end; address += PAGE_SIZE) {
+
+		if (vma->vm_flags & VM_MIXEDMAP)
+			ret = vmf_insert_mixed_prot(vma, address,
+						    __pfn_to_pfn_t(pfn, PFN_DEV),
+						    prot);
+		else
+			ret = vmf_insert_pfn_prot(vma, address, pfn, prot);
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL(ttm_bo_vm_dummy_page);
+
 vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf)
 {
 	struct vm_area_struct *vma = vmf->vma;
 	pgprot_t prot;
 	struct ttm_buffer_object *bo = vma->vm_private_data;
+	struct drm_device *ddev = bo->base.dev;
 	vm_fault_t ret;
+	int idx;
 
 	ret = ttm_bo_vm_reserve(bo, vmf);
 	if (ret)
 		return ret;
 
 	prot = vma->vm_page_prot;
-	ret = ttm_bo_vm_fault_reserved(vmf, prot, TTM_BO_VM_NUM_PREFAULT, 1);
+	if (drm_dev_enter(ddev, &idx)) {
+		ret = ttm_bo_vm_fault_reserved(vmf, prot, TTM_BO_VM_NUM_PREFAULT, 1);
+		drm_dev_exit(idx);
+	} else {
+		ret = ttm_bo_vm_dummy_page(vmf, prot);
+	}
 	if (ret == VM_FAULT_RETRY && !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT))
 		return ret;
 

include/drm/ttm/ttm_bo_api.h

@@ -620,4 +620,6 @@ int ttm_bo_vm_access(struct vm_area_struct *vma, unsigned long addr,
 		     void *buf, int len, int write);
 bool ttm_bo_delayed_delete(struct ttm_device *bdev, bool remove_all);
 
+vm_fault_t ttm_bo_vm_dummy_page(struct vm_fault *vmf, pgprot_t prot);
+
 #endif