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@xxxxxxxxx> Cc: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx> Suggested-by: Christian König <christian.koenig@xxxxxxx> Signed-off-by: Nirmoy Das <nirmoy.das@xxxxxxxxx> Reviewed-by: Christian König <christian.koenig@xxxxxxx>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, ThomasRegards, NirmoyRegards, Christian./ThomasIf 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;
