Re: [PATCH] Revert "arm64: dma: Drop cache invalidation from arch_dma_prep_coherent()"

[Manivannan Sadhasivam]

On Mon, Nov 28, 2022 at 06:44:13AM +0100, Thorsten Leemhuis wrote:
> On 14.11.22 12:03, 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.
> > [...]
> > [1] https://lore.kernel.org/linux-arm-kernel/CAMi1Hd1VBCFhf7+EXWHQWcGy4k=tcyLa7RGiFdprtRnegSG0Mw@xxxxxxxxxxxxxx/
> >
> 
> I have Amit's report on the list of tracked regressions. I also noticed
> the proposed change "arm64: dts: qcom: sc8280xp: fix PCIe DMA coherency":
> https://lore.kernel.org/all/20221124142501.29314-1-johan+linaro@xxxxxxxxxx/
> 
> I have no expertise in this area, but it looked somewhat related to my
> eyes, so please allow me to quickly ask: is that related or even
> supposed to fix Amit's regression?
> 

The proposed patch doesn't fix the regression reported by Amit. But the patch
itself fixes an issue that might be triggered more frequently by c44094eee32f.

Thanks,
Mani

> Ciao, Thorsten

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