Am 05.11.20 um 14:20 schrieb Daniel Vetter:
On Thu, Nov 05, 2020 at 01:56:22PM +0100, Christian König wrote:
Am 05.11.20 um 13:50 schrieb Daniel Vetter:
On Thu, Nov 05, 2020 at 01:29:50PM +0100, Christian König wrote:
Am 05.11.20 um 10:11 schrieb Daniel Vetter:
On Thu, Nov 5, 2020 at 9:00 AM Christian König <christian.koenig@xxxxxxx> 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@xxxxxxxxxx>
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@xxxxxxxxxx>
Reviewed-by: Brian Paul <brianp@xxxxxxxxxx>
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:
Why do you reject this?
When IOMMU is disabled or uses an 1 to 1 mapping we would otherwise give the
same access as /dev/mem to system memory and that is forbidden. But as I
noted this is just for the debugfs file.
Ah, there's a config option for that. Plus it's debugfs, anything goes in
debugfs, but if you're worried about that hole we should just disable the
entire debugfs file for CONFIG_STRICT_DEVMEM. I can perhaps throw that on
top, that follow_pfn patch series I'm baking is all about this kind of
fun.
And exactly that would get a NAK from us.
We have specially created that debugfs file as an alternative when
CONFIG_STRICT_DEVMEM is set.
Regards,
Christian.
When I tried a few years ago to not set the page->mapping I immediately ran
into issues with our eviction test. So I think that this is used elsewhere
as well.
That's the kind of interaction I'm worried about here tbh. If this does
some kind of shrinking of some sorts, I think a real shrinker should take
over.
An improved grep shows nothing else, so the only the above is the only
thing I can think of. What kind of eviction test goes boom if you clear
->mapping here? I'd be happy to type up the clever trick for the debugfs
files.
-Daniel
Regards,
Christian.
If this is to avoid issues with userptr, then I think there's a simple
trick:
- grab page reference
- recheck that the iova still points at the same address
- do read/write, safe in the knowledge that this page cannot be reused for
anything else
- drop page reference
Of course this can still race against iova updates, but that seems to be a
fundamental part of your debug interface here.
Or am I missing something?
Just pondering this more since setting the page->mapping pointer for just
this seems somewhat wild abuse of ->mapping semantics :-)
-Daniel
if (p->mapping != adev->mman.bdev.dev_mapping)
return -EPERM;
Christian.
-Daniel
Christian.
Cc: Thomas Hellstrom <thellstrom@xxxxxxxxxx>
Cc: Brian Paul <brianp@xxxxxxxxxx>
Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
Cc: Christian Koenig <christian.koenig@xxxxxxx>
Cc: Huang Rui <ray.huang@xxxxxxx>
---
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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