[PATCH v4 01/14] drm/ttm: Remap all page faults to per process dummy page.

[Alex Deucher]

On Mon, Jan 18, 2021 at 4:02 PM Andrey Grodzovsky
<andrey.grodzovsky at amd.com> wrote:
>
> 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.
>
> Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky at amd.com>
> ---
>  drivers/gpu/drm/ttm/ttm_bo_vm.c | 82 ++++++++++++++++++++++++++++++++++++++++-
>  include/drm/ttm/ttm_bo_api.h    |  2 +
>  2 files changed, 83 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> index 6dc96cf..ed89da3 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>
> @@ -380,25 +382,103 @@ 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 ttm_bo_device *bdev = bo->bdev;
> +       struct drm_device *ddev = bo->base.dev;
> +       vm_fault_t ret = VM_FAULT_NOPAGE;
> +       unsigned long address = vma->vm_start;
> +       unsigned long num_prefault = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
> +       unsigned long pfn;
> +       struct page *page;
> +       int i;
> +
> +       /*
> +        * Wait for buffer data in transit, due to a pipelined
> +        * move.
> +        */
> +       ret = ttm_bo_vm_fault_idle(bo, vmf);
> +       if (unlikely(ret != 0))
> +               return ret;
> +
> +       /* 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 (i = 0; i < num_prefault; ++i) {
> +
> +               if (unlikely(address >= vma->vm_end))
> +                       break;
> +
> +               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);
> +
> +               /* Never error on prefaulted PTEs */
> +               if (unlikely((ret & VM_FAULT_ERROR))) {
> +                       if (i == 0)
> +                               return VM_FAULT_NOPAGE;
> +                       else
> +                               break;
> +               }
> +
> +               address += PAGE_SIZE;
> +       }
> +
> +       /* 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;
> +
> +       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;
>
>         dma_resv_unlock(bo->base.resv);
>
>         return ret;
> +
> +       return ret;

Duplicate return here.

Alex

>  }
>  EXPORT_SYMBOL(ttm_bo_vm_fault);
>
> diff --git a/include/drm/ttm/ttm_bo_api.h b/include/drm/ttm/ttm_bo_api.h
> index e17be32..12fb240 100644
> --- a/include/drm/ttm/ttm_bo_api.h
> +++ b/include/drm/ttm/ttm_bo_api.h
> @@ -643,4 +643,6 @@ void ttm_bo_vm_close(struct vm_area_struct *vma);
>  int ttm_bo_vm_access(struct vm_area_struct *vma, unsigned long addr,
>                      void *buf, int len, int write);
>
> +vm_fault_t ttm_bo_vm_dummy_page(struct vm_fault *vmf, pgprot_t prot);
> +
>  #endif
> --
> 2.7.4
>
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