On Mon, Nov 14, 2022 at 04:33:29PM +0530, Manivannan Sadhasivam wrote:
This reverts commit c44094eee32f32f175aadc0efcac449d99b1bbf7.
As reported by Amit [1], dropping cache invalidation from
arch_dma_prep_coherent() triggers a crash on the Qualcomm SM8250 platform
(most probably on other Qcom platforms too). The reason is, Qcom
qcom_q6v5_mss driver copies the firmware metadata and shares it with modem
for validation. The modem has a secure block (XPU) that will trigger a
whole system crash if the shared memory is accessed by the CPU while modem
is poking at it.
To avoid this issue, the qcom_q6v5_mss driver allocates a chunk of memory
with no kernel mapping, vmap's it, copies the firmware metadata and
unvmap's it. Finally the address is then shared with modem for metadata
validation [2].
Now because of the removal of cache invalidation from
arch_dma_prep_coherent(), there will be cache lines associated with this
memory even after sharing with modem. So when the CPU accesses it, the XPU
violation gets triggered.
This last past is a non-sequitur: the buffer is no longer mapped on the CPU
side, so how would the CPU access it?
As I just replied to Amit, we need more information about what this
"access" is and how it is being detected.
Will