Re: [RFC PATCH v2 2/5] dma-mapping: Use the correct phys_to_dma() for DMA_RESTRICTED_POOL

Aneesh Kumar K.V
2026-04-13T06:08:42Z

Mostafa Saleh <smostafa@google.com> writes:

> As restricted dma pools are always decrypted, in swiotlb.c it uses
> phys_to_dma_unencrypted() for address conversion.
>
> However, in DMA-direct, calls to phys_to_dma_direct() with
> force_dma_unencrypted() returning false, will fallback to
> phys_to_dma() which is inconsistent for memory allocated from
> restricted dma pools.
>
> Fixes: f4111e39a52a ("swiotlb: Add restricted DMA alloc/free support")
> Signed-off-by: Mostafa Saleh <smostafa@google.com>
> ---
> kernel/dma/direct.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index 27d804f0473f..1a402bb956d9 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -26,7 +26,7 @@ u64 zone_dma_limit __ro_after_init = DMA_BIT_MASK(24);
> static inline dma_addr_t phys_to_dma_direct(struct device *dev,
> phys_addr_t phys)
> {
> - if (force_dma_unencrypted(dev))
> + if (force_dma_unencrypted(dev) || is_swiotlb_for_alloc(dev))
> return phys_to_dma_unencrypted(dev, phys);
>

So what kind of device is this? Is it a trusted device that needs to use
swiotlb in unencrypted form?(is that a valid use case?) Can we add additional comment
explaining the type of device for which we are allocating the DMA
buffer?

> return phys_to_dma(dev, phys);
> }
> --
> 2.53.0.1185.g05d4b7b318-goog

-aneesh