Re: [PATCH v6 1/2] drm/ttm: Add a flag to allow drivers to skip clear-on-free

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



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.



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;





[Index of Archives]     [Linux DRI Users]     [Linux Intel Graphics]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]     [XFree86]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Linux Kernel]     [Linux SCSI]     [XFree86]
  Powered by Linux