Re: [PATCH v3 1/3] accel/amdxdna: refuse an I/O memory mapping of an imported BO

[Christian König]

On 8/24/26 18:08, Lizhi Hou wrote:
> On 8/24/26 07:06, Christian König wrote:
>> On 8/17/26 19:53, Lizhi Hou wrote:
>>> On 8/13/26 09:46, Taimuraz Kaitmazov wrote:
>>>> amdxdna_gem_obj_vmap() takes whatever dma_buf_vmap() returns and only
>>>> rejects a NULL vaddr. iosys_map is discriminated by is_iomem, so an
>>>> exporter answering with an I/O mapping leaves a void __iomem pointer in
>>>> abo->mem.kva, which amdxdna_cmd_set_error() memsets and memcpys through.
>>>>
>>>> amdxdna_drm_va_tbl takes a dmabuf_fd, so such a BO can be any exporter's
>>>> buffer. amdgpu cannot reach this: its .pin forces GTT for a non peer to
>>>> peer attachment like ours. An exporter on drm_gem_prime_dmabuf_ops has
>>>> no .pin, and drm_gem_ttm_vmap() answers iomem for a VRAM resident
>>>> object, so an NPU paired with nouveau or radeon does.
>>>>
>>>> Refuse the mapping. vmw_gem_vmap() does the same; unlike that one this
>>>> path is reachable from an unprivileged ioctl, so it does not warn.
>>>>
>>>> Signed-off-by: Taimuraz Kaitmazov <taimuraz@xxxxxxxxxxxxx>
>>>> ---
>>>>    drivers/accel/amdxdna/amdxdna_gem.c | 10 ++++++++--
>>>>    1 file changed, 8 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/accel/amdxdna/amdxdna_gem.c b/drivers/accel/amdxdna/amdxdna_gem.c
>>>> index 1f190b319bb..b66ec9e4828 100644
>>>> --- a/drivers/accel/amdxdna/amdxdna_gem.c
>>>> +++ b/drivers/accel/amdxdna/amdxdna_gem.c
>>>> @@ -683,10 +683,16 @@ static int amdxdna_gem_obj_vmap(struct drm_gem_object *obj, struct iosys_map *ma
>>>>          dma_resv_assert_held(obj->resv);
>>>>    -    if (is_import_bo(abo))
>>>> +    if (is_import_bo(abo)) {
>>>>            ret = dma_buf_vmap(abo->dma_buf, map);
>> Mhm, why does amdxdna a vmap in the first place? For some workaround?
> 
> This is used for flushing the imported BO before. Based on our discussion before, the driver should not flush imported BO, so this becomes a invalid case.
> 
> On the other hand, vmap on a io_mem should not happen. So I suggested to move the check to amdxdna_gem_vmap() for an extra check.

Oh my, you should not use a vmap to flush CPU caches even if you own that GEM buffer! That is as buggy as it can be and most likely doesn't work 100% reliable.

What is the complete command submission flow here?

Regards,
Christian.

> 
> 
> Thanks,
> 
> Lizhi
> 
>>
>> Usually DMA-buf only provides that framebuffer emulation scanout inside the kernel.
>>
>> On the other hand as far as I can see that here should work correctly.
>>
>> Regards,
>> Christian.
>>
>>>> -    else
>>>> +        /* Callers use mem.kva as an ordinary kernel address. */
>>>> +        if (!ret && map->is_iomem) {
>>>> +            dma_buf_vunmap(abo->dma_buf, map);
>>>> +            return -EOPNOTSUPP;
>>>> +        }
>>> Thanks for the fix. The 'is_iomem' check should be moved to amdxdna_gem_vmap() to cover all the cases.
>>>
>>> Lizhi
>>>
>>>> +    } else {
>>>>            ret = drm_gem_shmem_object_vmap(obj, map);
>>>> +    }
>>>>        if (ret)
>>>>            return ret;
>>>>        if (!map->vaddr)