[PATCH v6 1/2] drm/ttm: Add a flag to allow drivers to skip clear-on-free
Nirmoy Das
nirmoy.das at intel.com
Wed Aug 21 10:22:07 UTC 2024
On 8/21/2024 10:08 AM, Thomas Hellström wrote:
> On Wed, 2024-08-21 at 09:47 +0200, Christian König wrote:
>> Am 20.08.24 um 18:46 schrieb Nirmoy Das:
>>> Hi Thomas, Christian,
>>>
>>> On 8/20/2024 5:47 PM, Christian König wrote:
>>>> Am 20.08.24 um 17:45 schrieb Thomas Hellström:
>>>>> On Tue, 2024-08-20 at 17:30 +0200, Christian König wrote:
>>>>>> Am 20.08.24 um 15:33 schrieb Thomas Hellström:
>>>>>>> Hi, Nirmoy, Christian
>>>>>>>
>>>>>>> On Fri, 2024-08-16 at 15:51 +0200, Nirmoy Das wrote:
>>>>>>>> Add TTM_TT_FLAG_CLEARED_ON_FREE, which DRM drivers can
>>>>>>>> set before
>>>>>>>> releasing backing stores if they want to skip clear-on-
>>>>>>>> free.
>>>>>>>>
>>>>>>>> Cc: Matthew Auld<matthew.auld at intel.com>
>>>>>>>> Cc: Thomas Hellström<thomas.hellstrom at linux.intel.com>
>>>>>>>> Suggested-by: Christian König<christian.koenig at amd.com>
>>>>>>>> Signed-off-by: Nirmoy Das<nirmoy.das at intel.com>
>>>>>>>> Reviewed-by: Christian König<christian.koenig at amd.com>
>>>>>>> What happens if two devices share the same global TTM pool
>>>>>>> type and one that does its own clearing. Wouldn't there
>>>>>>> be a
>>>>>>> pretty
>>>>>>> high chance that the the device that doesn't clear its own
>>>>>>> pages
>>>>>>> allocate non-cleared memory from the pool?
>>>>>> That's completely unproblematic. The flag indicates that the
>>>>>> released
>>>>>> pages are already cleared, if that isn't the case then the
>>>>>> flag
>>>>>> shouldn't be set on the TT object.
>>>>> Yeah, this patch is OK, but the way the follow-up xe patch uses
>>>>> it is
>>>>> problematic since, AFAICT, xe dma clears on alloc, meaning the
>>>>> pool
>>>>> pages are not cleared after use.
>>>> Yeah that is clearly invalid behavior.
>>>
>>> I was only thinking about one device use-case which won't leak any
>>> data though I am now miss-using the flag.
>>>
>>> If I skip dma clear for pooled BO then this flag is not really
>>> needed. Shall I revert the this and usage of
>>> TTM_TT_FLAG_CLEARED_ON_FREE
>>>
>>> and re-introduce it after I get a working clear on free
>>> implementation
>>> for XE?
>> Yes absolutely.
>>
>> I though that I made it clear that the handling should be that the
>> driver clears the pages and *then* sets the
>> TTM_TT_FLAG_CLEARED_ON_FREE
>> flag.
>>
>> So if you don't have the handling implemented like that then that's
>> clearly invalid behavior.
>>
>> Regards,
>> Christian.
> I agree.
> Revert and re-introduce as needed, and obtain an ack from Christian to
> merge through drm-xe-next before re-introduction so that it doesn't
> clash with anything planned elsewhere.
Sent a series to revert the usages TTM_TT_FLAG_CLEARED_ON_FREE.
Thanks both of you for your time and patience,
Nirmoy
>
> Thanks,
> Thomas
>
>
>
>>>
>>> Regards,
>>>
>>> Nirmoy
>>>
>>>
>>>> Regards,
>>>> Christian.
>>>>
>>>>> /Thomas
>>>>>
>>>>>> If one device clear it's pages and another device doesn't
>>>>>> clear it's
>>>>>> pages then we would just clear the pages of the device which
>>>>>> doesn't
>>>>>> do
>>>>>> it with a hardware DMA.
>>>>>>
>>>>>> Regards,
>>>>>> Christian.
>>>>>>
>>>>>>> /Thomas
>>>>>>>
>>>>>>>> ---
>>>>>>>> drivers/gpu/drm/ttm/ttm_pool.c | 18 +++++++++++-------
>>>>>>>> include/drm/ttm/ttm_tt.h | 6 +++++-
>>>>>>>> 2 files changed, 16 insertions(+), 8 deletions(-)
>>>>>>>>
>>>>>>>> diff --git a/drivers/gpu/drm/ttm/ttm_pool.c
>>>>>>>> b/drivers/gpu/drm/ttm/ttm_pool.c
>>>>>>>> index 8504dbe19c1a..935ab3cfd046 100644
>>>>>>>> --- a/drivers/gpu/drm/ttm/ttm_pool.c
>>>>>>>> +++ b/drivers/gpu/drm/ttm/ttm_pool.c
>>>>>>>> @@ -222,15 +222,18 @@ static void ttm_pool_unmap(struct
>>>>>>>> ttm_pool
>>>>>>>> *pool, dma_addr_t dma_addr,
>>>>>>>> }
>>>>>>>> /* Give pages into a specific pool_type */
>>>>>>>> -static void ttm_pool_type_give(struct ttm_pool_type *pt,
>>>>>>>> struct
>>>>>>>> page
>>>>>>>> *p)
>>>>>>>> +static void ttm_pool_type_give(struct ttm_pool_type *pt,
>>>>>>>> struct
>>>>>>>> page
>>>>>>>> *p,
>>>>>>>> + bool cleared)
>>>>>>>> {
>>>>>>>> unsigned int i, num_pages = 1 << pt->order;
>>>>>>>> - for (i = 0; i < num_pages; ++i) {
>>>>>>>> - if (PageHighMem(p))
>>>>>>>> - clear_highpage(p + i);
>>>>>>>> - else
>>>>>>>> - clear_page(page_address(p + i));
>>>>>>>> + if (!cleared) {
>>>>>>>> + for (i = 0; i < num_pages; ++i) {
>>>>>>>> + if (PageHighMem(p))
>>>>>>>> + clear_highpage(p + i);
>>>>>>>> + else
>>>>>>>> + clear_page(page_address(p + i));
>>>>>>>> + }
>>>>>>>> }
>>>>>>>> spin_lock(&pt->lock);
>>>>>>>> @@ -394,6 +397,7 @@ static void
>>>>>>>> ttm_pool_free_range(struct
>>>>>>>> ttm_pool
>>>>>>>> *pool, struct ttm_tt *tt,
>>>>>>>> pgoff_t start_page, pgoff_t
>>>>>>>> end_page)
>>>>>>>> {
>>>>>>>> struct page **pages = &tt->pages[start_page];
>>>>>>>> + bool cleared = tt->page_flags &
>>>>>>>> TTM_TT_FLAG_CLEARED_ON_FREE;
>>>>>>>> unsigned int order;
>>>>>>>> pgoff_t i, nr;
>>>>>>>> @@ -407,7 +411,7 @@ static void
>>>>>>>> ttm_pool_free_range(struct
>>>>>>>> ttm_pool
>>>>>>>> *pool, struct ttm_tt *tt,
>>>>>>>> pt = ttm_pool_select_type(pool, caching,
>>>>>>>> order);
>>>>>>>> if (pt)
>>>>>>>> - ttm_pool_type_give(pt, *pages);
>>>>>>>> + ttm_pool_type_give(pt, *pages, cleared);
>>>>>>>> else
>>>>>>>> ttm_pool_free_page(pool, caching, order,
>>>>>>>> *pages);
>>>>>>>> }
>>>>>>>> diff --git a/include/drm/ttm/ttm_tt.h
>>>>>>>> b/include/drm/ttm/ttm_tt.h
>>>>>>>> index 2b9d856ff388..cfaf49de2419 100644
>>>>>>>> --- a/include/drm/ttm/ttm_tt.h
>>>>>>>> +++ b/include/drm/ttm/ttm_tt.h
>>>>>>>> @@ -85,6 +85,9 @@ struct ttm_tt {
>>>>>>>> * fault handling abuses the DMA api a bit and
>>>>>>>> dma_map_attrs
>>>>>>>> can't be
>>>>>>>> * used to assure pgprot always matches.
>>>>>>>> *
>>>>>>>> + * TTM_TT_FLAG_CLEARED_ON_FREE: Set this if a drm
>>>>>>>> driver
>>>>>>>> handles
>>>>>>>> + * clearing backing store
>>>>>>>> + *
>>>>>>>> * TTM_TT_FLAG_PRIV_POPULATED: TTM internal only.
>>>>>>>> DO NOT
>>>>>>>> USE. This is
>>>>>>>> * set by TTM after ttm_tt_populate() has
>>>>>>>> successfully
>>>>>>>> returned, and is
>>>>>>>> * then unset when TTM calls ttm_tt_unpopulate().
>>>>>>>> @@ -94,8 +97,9 @@ struct ttm_tt {
>>>>>>>> #define TTM_TT_FLAG_EXTERNAL BIT(2)
>>>>>>>> #define TTM_TT_FLAG_EXTERNAL_MAPPABLE BIT(3)
>>>>>>>> #define TTM_TT_FLAG_DECRYPTED BIT(4)
>>>>>>>> +#define TTM_TT_FLAG_CLEARED_ON_FREE BIT(5)
>>>>>>>> -#define TTM_TT_FLAG_PRIV_POPULATED BIT(5)
>>>>>>>> +#define TTM_TT_FLAG_PRIV_POPULATED BIT(6)
>>>>>>>> uint32_t page_flags;
>>>>>>>> /** @num_pages: Number of pages in the page array.
>>>>>>>> */
>>>>>>>> uint32_t num_pages;
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