From: "Bhardwaj, Rajneesh" <rajneesh.bhardwaj@amd.com>
To: "Christian König" <christian.koenig@amd.com>,
"Christian König" <ckoenig.leichtzumerken@gmail.com>,
amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org
Cc: alexander.deucher@amd.com, daniel.vetter@ffwll.ch,
Felix Kuehling <Felix.Kuehling@amd.com>,
David Yat Sin <david.yatsin@amd.com>,
airlied@redhat.com
Subject: Re: [PATCH] drm/ttm: Don't inherit GEM object VMAs in child process
Date: Thu, 9 Dec 2021 10:29:46 -0500 [thread overview]
Message-ID: <cb5668d4-a13d-3b0b-442a-bfe1b3a7239a@amd.com> (raw)
In-Reply-To: <de272de9-3f4a-db40-699a-41394cb699dc@amd.com>
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.Kuehling@amd.com>
>>>>
>>>> Signed-off-by: David Yat Sin <david.yatsin@amd.com>
>>>> Signed-off-by: Rajneesh Bhardwaj <rajneesh.bhardwaj@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;
>>>> }
>>>
>
next prev parent reply other threads:[~2021-12-09 17:01 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-08 20:53 [PATCH] drm/ttm: Don't inherit GEM object VMAs in child process Rajneesh Bhardwaj
2021-12-09 7:54 ` Christian König
2021-12-09 15:23 ` Bhardwaj, Rajneesh
2021-12-09 15:27 ` Christian König
2021-12-09 15:29 ` Bhardwaj, Rajneesh [this message]
2021-12-09 15:30 ` Christian König
2021-12-09 18:28 ` Felix Kuehling
2021-12-10 6:58 ` Christian König
2021-12-20 9:29 ` Daniel Vetter
2021-12-20 18:12 ` Bhardwaj, Rajneesh
2021-12-22 20:53 ` Daniel Vetter
2021-12-23 1:49 ` Bhardwaj, Rajneesh
2021-12-23 1:51 ` Bhardwaj, Rajneesh
2021-12-23 7:05 ` Christian König
2022-01-04 18:08 ` Felix Kuehling
2022-01-05 8:08 ` Christian König
2022-01-05 16:16 ` Felix Kuehling
2022-01-05 16:27 ` Felix Kuehling
2022-01-06 9:05 ` Christian König
2022-01-06 16:45 ` Felix Kuehling
2022-01-06 16:48 ` Christian König
2022-01-06 16:51 ` Felix Kuehling
2022-01-07 8:56 ` Christian König
2022-01-07 17:47 ` Felix Kuehling
2022-01-14 16:44 ` Daniel Vetter
2022-01-14 17:26 ` Christian König
2022-01-14 17:40 ` Felix Kuehling
2022-01-17 11:44 ` Christian König
2022-01-17 14:17 ` Felix Kuehling
2022-01-17 14:21 ` Christian König
2022-01-17 14:34 ` Felix Kuehling
2022-01-17 14:50 ` Marek Olšák
2022-01-17 16:23 ` Christian König
2022-01-10 17:30 ` Bhardwaj, Rajneesh
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