On Mon, Jan 18, 2021 at 04:01:10PM -0500, Andrey Grodzovsky 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@xxxxxxx>
> ---
> 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);
I think we can lift this entire thing (once the ttm_bo_vm_fault_idle is
gone) to the drm level, since nothing ttm specific in here. Probably stuff
it into drm_gem.c (but really it's not even gem specific, it's fully
generic "replace this vma with dummy pages pls" function.
Aside from this nit I think the overall approach you have here is starting
to look good. Lots of work&polish, but imo we're getting there and can
start landing stuff soon.
-Daniel
> +
> 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;
> }
> 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
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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