[Mesa-dev] [PATCH] virgl: Use right key to insert resource to hash.

[Chia-I Wu]

You could end up having two virgl_hw_res with two different GEM handles
pointing to the same kernel GEM object.  That might break some assumptions
about dependency tracking.

For example, when the cmdbuf being built uses a buffer and you want to
transfer some more data into the buffer, you normally need to submit the
cmdbuf first before starting the transfer.  The current code detects that
with virgl_drm_res_is_ref, which assumes each kernel GEM object has a
unique virgl_hw_res.

On Mon, Apr 1, 2019 at 12:37 PM Lepton Wu <lepton at chromium.org> wrote:

>
>
>
> On Wed, Mar 20, 2019 at 3:03 PM Chia-I Wu <olvaffe at gmail.com> wrote:
>
>> On Mon, Mar 18, 2019 at 2:22 PM Lepton Wu <lepton at chromium.org> wrote:
>>
>>> The old code could use gem name as key when inserting it to bo_handles
>>> hash table while trying to remove it from hash table with bo_handle as
>>> key in virgl_hw_res_destroy. This triggers use after free. Also, we
>>> should only reuse resource from bo_handle hash when the handle type is
>>> FD.
>>>
>> Reuse is not very accurate.  Opening a shared handle (flink name) twice
>> gives two GEM handles.  Importing an fd handle (prime fd) twice gives the
>> same GEM handle.  In all cases, within a virgl_winsys, we want only one GEM
>> handle and only one virgl_resource for each kernel GEM object.
>>
>> I think the logic should go like:
>>
>>   if (HANDLE_TYPE_SHARED) {
>>     if (bo_names.has(flink_name))
>>       return bo_names[flink_name];
>>     gem_handle = gem_open(flink_name);
>>   } else {
>>     gem_handle = drmPrimeFDToHandle(prime_fd);
>>   }
>>
>>
>   if (bo_handles.has(gem_handle))
>>     return bo_handles[gem_handle];
>>   bo_handles[gem_handle] = create_new_resource();
>>
>> Hi, the current patch did most of what you said with only one
> difference:  it didn't insert to bo_handles[]   hash when the type
> is  HANDLE_TYPE_SHARED.
> I think this is reasonable since opening a shared handle always get a new
> gem handle very time and I think it doesn't worth to insert it to
> bo_handles[] hash.
> What do you think?
>
>>
>>> Signed-off-by: Lepton Wu <lepton at chromium.org>
>>> ---
>>>  src/gallium/winsys/virgl/drm/virgl_drm_winsys.c | 15 ++++++++-------
>>>  1 file changed, 8 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/src/gallium/winsys/virgl/drm/virgl_drm_winsys.c
>>> b/src/gallium/winsys/virgl/drm/virgl_drm_winsys.c
>>> index 120e8eda2cd..01811a0e997 100644
>>> --- a/src/gallium/winsys/virgl/drm/virgl_drm_winsys.c
>>> +++ b/src/gallium/winsys/virgl/drm/virgl_drm_winsys.c
>>> @@ -424,13 +424,13 @@ virgl_drm_winsys_resource_create_handle(struct
>>> virgl_winsys *qws,
>>>           res = NULL;
>>>           goto done;
>>>        }
>>> -   }
>>>
>>> -   res = util_hash_table_get(qdws->bo_handles,
>>> (void*)(uintptr_t)handle);
>>> -   if (res) {
>>> -      struct virgl_hw_res *r = NULL;
>>> -      virgl_drm_resource_reference(qdws, &r, res);
>>> -      goto done;
>>> +      res = util_hash_table_get(qdws->bo_handles,
>>> (void*)(uintptr_t)handle);
>>> +      if (res) {
>>> +        struct virgl_hw_res *r = NULL;
>>> +        virgl_drm_resource_reference(qdws, &r, res);
>>> +        goto done;
>>> +      }
>>>     }
>>>
>>>     res = CALLOC_STRUCT(virgl_hw_res);
>>> @@ -469,7 +469,8 @@ virgl_drm_winsys_resource_create_handle(struct
>>> virgl_winsys *qws,
>>>     res->num_cs_references = 0;
>>>     res->fence_fd = -1;
>>>
>>> -   util_hash_table_set(qdws->bo_handles, (void *)(uintptr_t)handle,
>>> res);
>>> +   util_hash_table_set(qdws->bo_handles, (void
>>> *)(uintptr_t)res->bo_handle,
>>> +                       res);
>>>
>>>  done:
>>>     mtx_unlock(&qdws->bo_handles_mutex);
>>> --
>>> 2.21.0.225.g810b269d1ac-goog
>>>
>>> _______________________________________________
>>> mesa-dev mailing list
>>> mesa-dev at lists.freedesktop.org
>>> https://lists.freedesktop.org/mailman/listinfo/mesa-dev
>>
>>
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