Re: [PATCH] drm/ttm: don't set page->mapping

From: "Christian König" <christian.koenig@amd.com>
To: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Daniel Vetter <daniel.vetter@intel.com>,
	Thomas Hellstrom <thellstrom@vmware.com>,
	Huang Rui <ray.huang@amd.com>, Brian Paul <brianp@vmware.com>,
	DRI Development <dri-devel@lists.freedesktop.org>
Subject: Re: [PATCH] drm/ttm: don't set page->mapping
Date: Thu, 5 Nov 2020 13:29:50 +0100	[thread overview]
Message-ID: <d6cdc22d-9cb2-7985-fdc3-ad3548899f02@amd.com> (raw)
In-Reply-To: <CAKMK7uGA3URvu3BUzs617sGS_TchHDhpzzgsMGrVVJtwBpD+Vw@mail.gmail.com>

Am 05.11.20 um 10:11 schrieb Daniel Vetter:
> On Thu, Nov 5, 2020 at 9:00 AM Christian König <christian.koenig@amd.com> wrote:
>> Am 04.11.20 um 17:50 schrieb Daniel Vetter:
>>> Random observation while trying to review Christian's patch series to
>>> stop looking at struct page for dma-buf imports.
>>>
>>> This was originally added in
>>>
>>> commit 58aa6622d32af7d2c08d45085f44c54554a16ed7
>>> Author: Thomas Hellstrom <thellstrom@vmware.com>
>>> Date:   Fri Jan 3 11:47:23 2014 +0100
>>>
>>>       drm/ttm: Correctly set page mapping and -index members
>>>
>>>       Needed for some vm operations; most notably unmap_mapping_range() with
>>>       even_cows = 0.
>>>
>>>       Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
>>>       Reviewed-by: Brian Paul <brianp@vmware.com>
>>>
>>> but we do not have a single caller of unmap_mapping_range with
>>> even_cows == 0. And all the gem drivers don't do this, so another
>>> small thing we could standardize between drm and ttm drivers.
>>>
>>> Plus I don't really see a need for unamp_mapping_range where we don't
>>> want to indiscriminately shoot down all ptes.
>> NAK, we use this to determine if a pages belongs to the driver or not in
>> amdgpu for example.
>>
>> Mostly used for debugging, but I would really like to keep that.
> Can you pls point me at that code? A quick grep hasn't really found much at all.

See amdgpu_iomem_read() for an example:

>                 if (p->mapping != adev->mman.bdev.dev_mapping)
>                         return -EPERM;

Christian.

> -Daniel
>
>> Christian.
>>
>>> Cc: Thomas Hellstrom <thellstrom@vmware.com>
>>> Cc: Brian Paul <brianp@vmware.com>
>>> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
>>> Cc: Christian Koenig <christian.koenig@amd.com>
>>> Cc: Huang Rui <ray.huang@amd.com>
>>> ---
>>>    drivers/gpu/drm/ttm/ttm_tt.c | 12 ------------
>>>    1 file changed, 12 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/ttm/ttm_tt.c b/drivers/gpu/drm/ttm/ttm_tt.c
>>> index 8861a74ac335..438ea43fd8c1 100644
>>> --- a/drivers/gpu/drm/ttm/ttm_tt.c
>>> +++ b/drivers/gpu/drm/ttm/ttm_tt.c
>>> @@ -291,17 +291,6 @@ int ttm_tt_swapout(struct ttm_bo_device *bdev, struct ttm_tt *ttm)
>>>        return ret;
>>>    }
>>>
>>> -static void ttm_tt_add_mapping(struct ttm_bo_device *bdev, struct ttm_tt *ttm)
>>> -{
>>> -     pgoff_t i;
>>> -
>>> -     if (ttm->page_flags & TTM_PAGE_FLAG_SG)
>>> -             return;
>>> -
>>> -     for (i = 0; i < ttm->num_pages; ++i)
>>> -             ttm->pages[i]->mapping = bdev->dev_mapping;
>>> -}
>>> -
>>>    int ttm_tt_populate(struct ttm_bo_device *bdev,
>>>                    struct ttm_tt *ttm, struct ttm_operation_ctx *ctx)
>>>    {
>>> @@ -320,7 +309,6 @@ int ttm_tt_populate(struct ttm_bo_device *bdev,
>>>        if (ret)
>>>                return ret;
>>>
>>> -     ttm_tt_add_mapping(bdev, ttm);
>>>        ttm->page_flags |= TTM_PAGE_FLAG_PRIV_POPULATED;
>>>        if (unlikely(ttm->page_flags & TTM_PAGE_FLAG_SWAPPED)) {
>>>                ret = ttm_tt_swapin(ttm);
>

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