On Sun, Jun 21, 2020 at 02:03:02AM -0400, Andrey Grodzovsky wrote:
> On device removal reroute all CPU mappings to dummy page per drm_file
> instance or imported GEM object.
>
> Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@xxxxxxx>
> ---
> drivers/gpu/drm/ttm/ttm_bo_vm.c | 65 ++++++++++++++++++++++++++++++++++++-----
> 1 file changed, 57 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> index 389128b..2f8bf5e 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> @@ -35,6 +35,8 @@
> #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_file.h>
> #include <linux/mm.h>
> #include <linux/pfn_t.h>
> #include <linux/rbtree.h>
> @@ -328,19 +330,66 @@ vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf)
Hm I think diff and code flow look a bit bad now. What about renaming the
current function to __ttm_bo_vm_fault and then having something like the
below:
ttm_bo_vm_fault(args) {
if (drm_dev_enter()) {
__ttm_bo_vm_fault(args);
drm_dev_exit();
} else {
drm_gem_insert_dummy_pfn();
}
}
I think drm_gem_insert_dummy_pfn(); should be portable across drivers, so
another nice point to try to unifiy drivers as much as possible.
-Daniel
> pgprot_t prot;
> struct ttm_buffer_object *bo = vma->vm_private_data;
> vm_fault_t ret;
> + int idx;
> + struct drm_device *ddev = bo->base.dev;
>
> - ret = ttm_bo_vm_reserve(bo, vmf);
> - if (ret)
> - return ret;
> + if (drm_dev_enter(ddev, &idx)) {
> + ret = ttm_bo_vm_reserve(bo, vmf);
> + if (ret)
> + goto exit;
> +
> + prot = vma->vm_page_prot;
>
> - prot = vma->vm_page_prot;
> - ret = ttm_bo_vm_fault_reserved(vmf, prot, TTM_BO_VM_NUM_PREFAULT);
> - if (ret == VM_FAULT_RETRY && !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT))
> + ret = ttm_bo_vm_fault_reserved(vmf, prot, TTM_BO_VM_NUM_PREFAULT);
> + if (ret == VM_FAULT_RETRY && !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT))
> + goto exit;
> +
> + dma_resv_unlock(bo->base.resv);
> +
> +exit:
> + drm_dev_exit(idx);
> return ret;
> + } else {
>
> - dma_resv_unlock(bo->base.resv);
> + struct drm_file *file = NULL;
> + struct page *dummy_page = NULL;
> + int handle;
>
> - return ret;
> + /* We are faulting on imported BO from dma_buf */
> + if (bo->base.dma_buf && bo->base.import_attach) {
> + dummy_page = bo->base.dummy_page;
> + /* We are faulting on non imported BO, find drm_file owning the BO*/
Uh, we can't fish that out of the vma->vm_file pointer somehow? Or is that
one all wrong? Doing this kind of list walk looks pretty horrible.
If the vma doesn't have the right pointer I guess next option is that we
store the drm_file page in gem_bo->dummy_page, and replace it on first
export. But that's going to be tricky to track ...
> + } else {
> + struct drm_gem_object *gobj;
> +
> + mutex_lock(&ddev->filelist_mutex);
> + list_for_each_entry(file, &ddev->filelist, lhead) {
> + spin_lock(&file->table_lock);
> + idr_for_each_entry(&file->object_idr, gobj, handle) {
> + if (gobj == &bo->base) {
> + dummy_page = file->dummy_page;
> + break;
> + }
> + }
> + spin_unlock(&file->table_lock);
> + }
> + mutex_unlock(&ddev->filelist_mutex);
> + }
> +
> + if (dummy_page) {
> + /*
> + * Let do_fault complete the PTE install e.t.c using vmf->page
> + *
> + * TODO - should i call free_page somewhere ?
Nah, instead don't call get_page. The page will be around as long as
there's a reference for the drm_file or gem_bo, which is longer than any
mmap. Otherwise yes this would like really badly.
> + */
> + get_page(dummy_page);
> + vmf->page = dummy_page;
> + return 0;
> + } else {
> + return VM_FAULT_SIGSEGV;
Hm that would be a kernel bug, wouldn't it? WARN_ON() required here imo.
-Daniel
> + }
> + }
> }
> EXPORT_SYMBOL(ttm_bo_vm_fault);
>
> --
> 2.7.4
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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