[PATCH 1/2] drm/amdgpu: fix KFDMemoryTest.PtraceAccessInvisibleVram fail on SRIOV

[Felix Kuehling]

On 2024-08-12 02:59, Samuel Zhang wrote:
> Ptrace access VRAM bo will first try sdma access in
> amdgpu_ttm_access_memory_sdma(), if fails, it will fallback to mmio
> access.
>
> Since ptrace only access 8 bytes at a time and
> amdgpu_ttm_access_memory_sdma() only allow PAGE_SIZE bytes access,
> it returns fail.
> On SRIOV, mmio access will also fail as MM_INDEX/MM_DATA register write
> is blocked for security reasons.
>
> The fix is just change len check in amdgpu_ttm_access_memory_sdma() so
> that len in (0, PAGE_SIZE] are allowed. This will not only fix the ptrace
> test case on SRIOV, but also improve the access performance when the
> access length is < PAGE_SIZE.
> len > PAGE_SIZE case support is not needed as larger size will be break
> into chunks of PAGE_SIZE len max in mem_rw().
>
> Signed-off-by: Samuel Zhang <guoqing.zhang at amd.com>
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> index 5daa05e23ddf..a6e90eada367 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> @@ -1486,7 +1486,7 @@ static int amdgpu_ttm_access_memory_sdma(struct ttm_buffer_object *bo,
>   	unsigned int num_dw;
>   	int r, idx;
>   
> -	if (len != PAGE_SIZE)
> +	if (len > PAGE_SIZE)
OK, I'll spell it out explicitly. This needs an SRIOV VF-specific 
condition if you want to allow smaller accesses with SDMA on SRIOV. On 
bare metal we want to be able to fall back to the FB BAR for smaller 
accesses. On a VF it will use SDMA for everything.

	if (!amdgpu_sriov_vf(adev) && len != PAGE_SIZE)
		return -EINVAL;


Regards,
   Felix


>   		return -EINVAL;
>   
>   	if (!adev->mman.sdma_access_ptr)
> @@ -1514,7 +1514,7 @@ static int amdgpu_ttm_access_memory_sdma(struct ttm_buffer_object *bo,
>   		swap(src_addr, dst_addr);
>   
>   	amdgpu_emit_copy_buffer(adev, &job->ibs[0], src_addr, dst_addr,
> -				PAGE_SIZE, 0);
> +				len, 0);
>   
>   	amdgpu_ring_pad_ib(adev->mman.buffer_funcs_ring, &job->ibs[0]);
>   	WARN_ON(job->ibs[0].length_dw > num_dw);