Re: [PATCH] drm/amdgpu: Fix a potential sdma invalid access

["Christian König" <ckoenig.leichtzumerken@gmail.com>]

Hi Qu,

Am 06.04.21 um 08:04 schrieb Qu Huang:
> Hi Christian,
>
> On 2021/4/3 16:49, Christian König wrote:
>> Hi Qu,
>>
>> Am 03.04.21 um 07:08 schrieb Qu Huang:
>>> Hi Christian,
>>>
>>> On 2021/4/3 0:25, Christian König wrote:
>>>> Hi Qu,
>>>>
>>>> Am 02.04.21 um 05:18 schrieb Qu Huang:
>>>>> Before dma_resv_lock(bo->base.resv, NULL) in
>>>>> amdgpu_bo_release_notify(),
>>>>> the bo->base.resv lock may be held by ttm_mem_evict_first(),
>>>>
>>>> That can't happen since when bo_release_notify is called the BO has 
>>>> not
>>>> more references and is therefore deleted.
>>>>
>>>> And we never evict a deleted BO, we just wait for it to become idle.
>>>>
>>> Yes, the bo reference counter return to zero will enter
>>> ttm_bo_release(),but notify bo release (call 
>>> amdgpu_bo_release_notify())
>>> first happen, and then test if a reservation object's fences have been
>>> signaled, and then mark bo as deleted and remove bo from the LRU list.
>>>
>>> When ttm_bo_release() and ttm_mem_evict_first() is concurrent,
>>> the Bo has not been removed from the LRU list and is not marked as
>>> deleted, this will happen.
>>
>> Not sure on which code base you are, but I don't see how this can 
>> happen.
>>
>> ttm_mem_evict_first() calls ttm_bo_get_unless_zero() and
>> ttm_bo_release() is only called when the BO reference count becomes 
>> zero.
>>
>> So ttm_mem_evict_first() will see that this BO is about to be destroyed
>> and skips it.
>>
>
> Yes, you are right. My version of TTM is ROCM 3.3, so
> ttm_mem_evict_first() did not call ttm_bo_get_unless_zero(), check that
> ROCM 4.0 ttm doesn't have this issue. This is an oversight on my part.
>
>>>
>>> As a test, when we use CPU memset instead of SDMA fill in
>>> amdgpu_bo_release_notify(), the result is page fault:
>>>
>>> PID: 5490   TASK: ffff8e8136e04100  CPU: 4   COMMAND: "gemmPerf"
>>>   #0 [ffff8e79eaa17970] machine_kexec at ffffffffb2863784
>>>   #1 [ffff8e79eaa179d0] __crash_kexec at ffffffffb291ce92
>>>   #2 [ffff8e79eaa17aa0] crash_kexec at ffffffffb291cf80
>>>   #3 [ffff8e79eaa17ab8] oops_end at ffffffffb2f6c768
>>>   #4 [ffff8e79eaa17ae0] no_context at ffffffffb2f5aaa6
>>>   #5 [ffff8e79eaa17b30] __bad_area_nosemaphore at ffffffffb2f5ab3d
>>>   #6 [ffff8e79eaa17b80] bad_area_nosemaphore at ffffffffb2f5acae
>>>   #7 [ffff8e79eaa17b90] __do_page_fault at ffffffffb2f6f6c0
>>>   #8 [ffff8e79eaa17c00] do_page_fault at ffffffffb2f6f925
>>>   #9 [ffff8e79eaa17c30] page_fault at ffffffffb2f6b758
>>>      [exception RIP: memset+31]
>>>      RIP: ffffffffb2b8668f  RSP: ffff8e79eaa17ce8  RFLAGS: 00010a17
>>>      RAX: bebebebebebebebe  RBX: ffff8e747bff10c0  RCX: 
>>> 0000060b00200000
>>>      RDX: 0000000000000000  RSI: 00000000000000be  RDI: 
>>> ffffab807f000000
>>>      RBP: ffff8e79eaa17d10   R8: ffff8e79eaa14000   R9: 
>>> ffffab7c80000000
>>>      R10: 000000000000bcba  R11: 00000000000001ba  R12: 
>>> ffff8e79ebaa4050
>>>      R13: ffffab7c80000000  R14: 0000000000022600  R15: 
>>> ffff8e8136e04100
>>>      ORIG_RAX: ffffffffffffffff  CS: 0010  SS: 0018
>>> #10 [ffff8e79eaa17ce8] amdgpu_bo_release_notify at ffffffffc092f2d1
>>> [amdgpu]
>>> #11 [ffff8e79eaa17d18] ttm_bo_release at ffffffffc08f39dd [amdttm]
>>> #12 [ffff8e79eaa17d58] amdttm_bo_put at ffffffffc08f3c8c [amdttm]
>>> #13 [ffff8e79eaa17d68] amdttm_bo_vm_close at ffffffffc08f7ac9 [amdttm]
>>> #14 [ffff8e79eaa17d80] remove_vma at ffffffffb29ef115
>>> #15 [ffff8e79eaa17da0] exit_mmap at ffffffffb29f2c64
>>> #16 [ffff8e79eaa17e58] mmput at ffffffffb28940c7
>>> #17 [ffff8e79eaa17e78] do_exit at ffffffffb289dc95
>>> #18 [ffff8e79eaa17f10] do_group_exit at ffffffffb289e4cf
>>> #19 [ffff8e79eaa17f40] sys_exit_group at ffffffffb289e544
>>> #20 [ffff8e79eaa17f50] system_call_fastpath at ffffffffb2f74ddb
>>
>> Well that might be perfectly expected. VRAM is not necessarily CPU
>> accessible.
>>
> As a test，use CPU memset instead of SDMA fill, This is my code:
> void amdgpu_bo_release_notify(struct ttm_buffer_object *bo)
> {
>     struct amdgpu_bo *abo;
>     uint64_t num_pages;
>     struct drm_mm_node *mm_node;
>     struct amdgpu_device *adev;
>     void __iomem *kaddr;
>
>     if (!amdgpu_bo_is_amdgpu_bo(bo))
>         return;
>
>     abo = ttm_to_amdgpu_bo(bo);
>     num_pages = abo->tbo.num_pages;
>     mm_node = abo->tbo.mem.mm_node;
>     adev = amdgpu_ttm_adev(abo->tbo.bdev);
>     kaddr = adev->mman.aper_base_kaddr;
>
>     if (abo->kfd_bo)
>         amdgpu_amdkfd_unreserve_memory_limit(abo);
>
>     if (bo->mem.mem_type != TTM_PL_VRAM || !bo->mem.mm_node ||
>         !(abo->flags & AMDGPU_GEM_CREATE_VRAM_WIPE_ON_RELEASE))
>         return;
>
>     dma_resv_lock(amdkcl_ttm_resvp(bo), NULL);
>     while (num_pages && mm_node) {
>         void *ptr = kaddr + (mm_node->start << PAGE_SHIFT);

That might not work as expected.

aper_base_kaddr can only point to a 256MiB window into VRAM, but VRAM 
itself is usually much larger.

So your memset_io() might end up in nirvana if the BO is allocated 
outside of the window.

> memset_io(ptr, AMDGPU_POISON & 0xff, mm_node->size <<PAGE_SHIFT);
>         num_pages -= mm_node->size;
>         ++mm_node;
>     }
>     dma_resv_unlock(amdkcl_ttm_resvp(bo));
> }
>
>
>
>
>
> I have used the old version through oversight, so I am sorry for your
> trouble.

No, problem. I was just wondering if I was missing something.

Regards,
Christian.

>
>
> Regards,
> Qu.
>
>> Regards,
>> Christian.
>>
>>>
>>> Regards,
>>> Qu.
>>>
>>>
>>>> Regards,
>>>> Christian.
>>>>
>>>>> and the VRAM mem will be evicted, mem region was replaced
>>>>> by Gtt mem region. amdgpu_bo_release_notify() will then
>>>>> hold the bo->base.resv lock, and SDMA will get an invalid
>>>>> address in amdgpu_fill_buffer(), resulting in a VMFAULT
>>>>> or memory corruption.
>>>>>
>>>>> To avoid it, we have to hold bo->base.resv lock first, and
>>>>> check whether the mem.mem_type is TTM_PL_VRAM.
>>>>>
>>>>> Signed-off-by: Qu Huang <jinsdb@126.com>
>>>>> ---
>>>>>   drivers/gpu/drm/amd/amdgpu/amdgpu_object.c | 8 ++++++--
>>>>>   1 file changed, 6 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
>>>>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
>>>>> index 4b29b82..8018574 100644
>>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
>>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
>>>>> @@ -1300,12 +1300,16 @@ void amdgpu_bo_release_notify(struct
>>>>> ttm_buffer_object *bo)
>>>>>       if (bo->base.resv == &bo->base._resv)
>>>>>           amdgpu_amdkfd_remove_fence_on_pt_pd_bos(abo);
>>>>>
>>>>> -    if (bo->mem.mem_type != TTM_PL_VRAM || !bo->mem.mm_node ||
>>>>> -        !(abo->flags & AMDGPU_GEM_CREATE_VRAM_WIPE_ON_RELEASE))
>>>>> +    if (!(abo->flags & AMDGPU_GEM_CREATE_VRAM_WIPE_ON_RELEASE))
>>>>>           return;
>>>>>
>>>>>       dma_resv_lock(bo->base.resv, NULL);
>>>>>
>>>>> +    if (bo->mem.mem_type != TTM_PL_VRAM || !bo->mem.mm_node) {
>>>>> +        dma_resv_unlock(bo->base.resv);
>>>>> +        return;
>>>>> +    }
>>>>> +
>>>>>       r = amdgpu_fill_buffer(abo, AMDGPU_POISON, bo->base.resv,
>>>>> &fence);
>>>>>       if (!WARN_ON(r)) {
>>>>>           amdgpu_bo_fence(abo, fence, false);
>>>>> -- 
>>>>> 1.8.3.1
>>>>>
>>>
>
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