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

Manivannan Sadhasivam
2022-11-14T11:30:17Z

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

s/SM8250/SDM845/g

Sorry for the confusion.

Thanks,
Mani

> (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.
>
> So let's revert this commit to get remoteproc's working (thereby avoiding
> full system crash) on Qcom platforms.
>
> [1] https://lore.kernel.org/linux-arm-kernel/CAMi1Hd1VBCFhf7+EXWHQWcGy4k=tcyLa7RGiFdprtRnegSG0Mw@mail.gmail.com/
> [2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/remoteproc/qcom_q6v5_mss.c#n933
>
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> ---
>
> Will, Catalin: Please share if you have any other suggestions to handle the
> resource sharing in the remoteproc driver that could avoid this revert.
>
> arch/arm64/mm/dma-mapping.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
> index 3cb101e8cb29..7d7e9a046305 100644
> --- a/arch/arm64/mm/dma-mapping.c
> +++ b/arch/arm64/mm/dma-mapping.c
> @@ -36,7 +36,7 @@ void arch_dma_prep_coherent(struct page *page, size_t size)
> {
> unsigned long start = (unsigned long)page_address(page);
>
> - dcache_clean_poc(start, start + size);
> + dcache_clean_inval_poc(start, start + size);
> }
>
> #ifdef CONFIG_IOMMU_DMA
> --
> 2.25.1
>

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