Re: [PATCH v6 01/16] drm/ttm: Remap all page faults to per process dummy page.

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On 2021-05-11 2:38 a.m., Christian König wrote:
Am 10.05.21 um 18:36 schrieb Andrey Grodzovsky:
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 superflous code.

Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@xxxxxxx>
---
  drivers/gpu/drm/ttm/ttm_bo_vm.c | 57 ++++++++++++++++++++++++++++++++-
  include/drm/ttm/ttm_bo_api.h    |  2 ++
  2 files changed, 58 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
index b31b18058965..e5a9615519d1 100644
--- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
+++ b/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 +382,72 @@ 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;
+
+    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 (unlikely(address >= vma->vm_end))
+            break;

That extra check can be removed as far as I can see.


+
+        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);
+    }
+

+    /* 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;

You should probably move that before inserting the page into the VMA and also free the allocated page if it goes wrong.


drmm_add_action_or_reset will automatically release the page if the add action fails, that the 'reset' part of the function.

Andrey



Apart from that patch looks good to me,
Christian.

+
+    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;
  diff --git a/include/drm/ttm/ttm_bo_api.h b/include/drm/ttm/ttm_bo_api.h
index 639521880c29..254ede97f8e3 100644
--- a/include/drm/ttm/ttm_bo_api.h
+++ b/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

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