On 12/20/2021 4:29 AM, Daniel Vetter wrote:
On Fri, Dec 10, 2021 at 07:58:50AM +0100, Christian König wrote:
Am 09.12.21 um 19:28 schrieb Felix Kuehling:
Am 2021-12-09 um 10:30 a.m. schrieb Christian König:
That still won't work.
But I think we could do this change for the amdgpu mmap callback only.
If graphics user mode has problems with it, we could even make this
specific to KFD BOs in the amdgpu_gem_object_mmap callback.
I think it's fine for the whole amdgpu stack, my concern is more about
radeon, nouveau and the ARM stacks which are using this as well.
That blew up so nicely the last time we tried to change it and I know of at
least one case where radeon was/is used with BOs in a child process.
I'm way late and burried again, but I think it'd be good to be consistent
here across drivers. Or at least across drm drivers. And we've had the vma
open/close refcounting to make fork work since forever.
I think if we do this we should really only do this for mmap() where this
applies, but reading through the thread here I'm honestly confused why
this is a problem. If CRIU can't handle forked mmaps it needs to be
thought that, not hacked around. Or at least I'm not understanding why
this shouldn't work ...
-Daniel
Hi Daniel
In the v2
https://lore.kernel.org/all/a1a865f5-ad2c-29c8-cbe4-2635d53ec...@amd.com/T/
I pretty much limited the scope of the change to KFD BOs on mmap.
Regarding CRIU, I think its not a CRIU problem as CRIU on restore, only
tries to recreate all the child processes and then mmaps all the VMAs it
sees (as per checkpoint snapshot) in the new process address space after
the VMA placements are finalized in the position independent code phase.
Since the inherited VMAs don't have access rights the criu mmap fails.
Regards,
Rajneesh
Regards,
Christian.
Regards,
Felix
Regards,
Christian.
Am 09.12.21 um 16:29 schrieb Bhardwaj, Rajneesh:
Sounds good. I will send a v2 with only ttm_bo_mmap_obj change. Thank
you!
On 12/9/2021 10:27 AM, Christian König wrote:
Hi Rajneesh,
yes, separating this from the drm_gem_mmap_obj() change is certainly
a good idea.
The child cannot access the BOs mapped by the parent anyway with
access restrictions applied
exactly that is not correct. That behavior is actively used by some
userspace stacks as far as I know.
Regards,
Christian.
Am 09.12.21 um 16:23 schrieb Bhardwaj, Rajneesh:
Thanks Christian. Would it make it less intrusive if I just use the
flag for ttm bo mmap and remove the drm_gem_mmap_obj change from
this patch? For our use case, just the ttm_bo_mmap_obj change
should suffice and we don't want to put any more work arounds in
the user space (thunk, in our case).
The child cannot access the BOs mapped by the parent anyway with
access restrictions applied so I wonder why even inherit the vma?
On 12/9/2021 2:54 AM, Christian König wrote:
Am 08.12.21 um 21:53 schrieb Rajneesh Bhardwaj:
When an application having open file access to a node forks, its
shared
mappings also get reflected in the address space of child process
even
though it cannot access them with the object permissions applied.
With the
existing permission checks on the gem objects, it might be
reasonable to
also create the VMAs with VM_DONTCOPY flag so a user space
application
doesn't need to explicitly call the madvise(addr, len,
MADV_DONTFORK)
system call to prevent the pages in the mapped range to appear in
the
address space of the child process. It also prevents the memory
leaks
due to additional reference counts on the mapped BOs in the child
process that prevented freeing the memory in the parent for which
we had
worked around earlier in the user space inside the thunk library.
Additionally, we faced this issue when using CRIU to checkpoint
restore
an application that had such inherited mappings in the child which
confuse CRIU when it mmaps on restore. Having this flag set for the
render node VMAs helps. VMAs mapped via KFD already take care of
this so
this is needed only for the render nodes.
Unfortunately that is most likely a NAK. We already tried
something similar.
While it is illegal by the OpenGL specification and doesn't work
for most userspace stacks, we do have some implementations which
call fork() with a GL context open and expect it to work.
Regards,
Christian.
Cc: Felix Kuehling <felix.kuehl...@amd.com>
Signed-off-by: David Yat Sin <david.yat...@amd.com>
Signed-off-by: Rajneesh Bhardwaj <rajneesh.bhard...@amd.com>
---
drivers/gpu/drm/drm_gem.c | 3 ++-
drivers/gpu/drm/ttm/ttm_bo_vm.c | 2 +-
2 files changed, 3 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
index 09c820045859..d9c4149f36dd 100644
--- a/drivers/gpu/drm/drm_gem.c
+++ b/drivers/gpu/drm/drm_gem.c
@@ -1058,7 +1058,8 @@ int drm_gem_mmap_obj(struct drm_gem_object
*obj, unsigned long obj_size,
goto err_drm_gem_object_put;
}
- vma->vm_flags |= VM_IO | VM_PFNMAP | VM_DONTEXPAND |
VM_DONTDUMP;
+ vma->vm_flags |= VM_IO | VM_PFNMAP | VM_DONTEXPAND
+ | VM_DONTDUMP | VM_DONTCOPY;
vma->vm_page_prot =
pgprot_writecombine(vm_get_page_prot(vma->vm_flags));
vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);
}
diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c
b/drivers/gpu/drm/ttm/ttm_bo_vm.c
index 33680c94127c..420a4898fdd2 100644
--- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
@@ -566,7 +566,7 @@ int ttm_bo_mmap_obj(struct vm_area_struct
*vma, struct ttm_buffer_object *bo)
vma->vm_private_data = bo;
- vma->vm_flags |= VM_PFNMAP;
+ vma->vm_flags |= VM_PFNMAP | VM_DONTCOPY;
vma->vm_flags |= VM_IO | VM_DONTEXPAND | VM_DONTDUMP;
return 0;
}
