[PATCH] drm/ttm: make sure pool pages are cleared

[Christian König]

Am 10.02.21 um 19:15 schrieb Daniel Vetter:
> On Wed, Feb 10, 2021 at 5:05 PM Christian König
> <ckoenig.leichtzumerken at gmail.com> wrote:
>> The old implementation wasn't consistend on this.
>>
>> But it looks like we depend on this so better bring it back.
>>
>> Signed-off-by: Christian König <christian.koenig at amd.com>
>> Reported-and-tested-by: Mike Galbraith <efault at gmx.de>
>> Fixes: d099fc8f540a ("drm/ttm: new TT backend allocation pool v3")
> Well I think in general there's a bit an issue in ttm with not
> clearing stuff everywhere. So definitely in favour of clearing stuff.
> Looking at the code this only fixes the clearing, at alloc time we're
> still very optional with clearing. I think we should just set
> __GFP_ZERO unconditionally there too.

No, the alloc handling is actually correct.

We are clearing only when we allocate pages for userspace. Not for the 
kernel nor for eviction when pages are overwritten anyway.

The key point is that the old page pool was ignoring the flag for this 
in some code paths and I wasn't sure if that's still necessary or not.

Turned out it was necessary after all.

Thanks,
Christian.

>
> With that: Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
>
>> ---
>>   drivers/gpu/drm/ttm/ttm_pool.c | 10 ++++++++++
>>   1 file changed, 10 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/ttm/ttm_pool.c b/drivers/gpu/drm/ttm/ttm_pool.c
>> index 74bf1c84b637..6e27cb1bf48b 100644
>> --- a/drivers/gpu/drm/ttm/ttm_pool.c
>> +++ b/drivers/gpu/drm/ttm/ttm_pool.c
>> @@ -33,6 +33,7 @@
>>
>>   #include <linux/module.h>
>>   #include <linux/dma-mapping.h>
>> +#include <linux/highmem.h>
>>
>>   #ifdef CONFIG_X86
>>   #include <asm/set_memory.h>
>> @@ -218,6 +219,15 @@ 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)
>>   {
>> +       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));
>> +       }
>> +
>>          spin_lock(&pt->lock);
>>          list_add(&p->lru, &pt->pages);
>>          spin_unlock(&pt->lock);
>> --
>> 2.25.1
>>
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>
>