lkml.org 
[lkml]   [2022]   [Nov]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] Revert "arm64: dma: Drop cache invalidation from arch_dma_prep_coherent()"
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

\
 
 \ /
  Last update: 2022-11-14 15:11    [W:0.271 / U:0.544 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site