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

[Andrey Grodzovsky]

Hey Daniel, just a ping.

Andrey

On 1/25/21 10:28 AM, Andrey Grodzovsky wrote:
>
> On 1/19/21 8:56 AM, Daniel Vetter wrote:
>> 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 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);
>> 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.
>
>
> Once I started with this I noticed that drmm_add_action_or_reset depends
> on struct drm_device *ddev = bo->base.dev  and bo is the private data
> we embed at the TTM level when setting up the mapping and so this forces
> to move drmm_add_action_or_reset out of this function to every client who uses
> this function, and then you separate the logic of page allocation from it's 
> release.
> So I suggest we keep it as is.
>
> Andrey
>
>
>>
>> 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
>>>