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

Jason Gunthorpe
2026-03-30T15:09:06Z

On Mon, Mar 30, 2026 at 02:50:40PM +0000, Mostafa Saleh wrote:
> 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);

Same remark, I think the force_dma_unencrypted() was a hack to make up
for a flag here. In these lower layers we need to annotate if phys is
encrypted/decrypted and take the proper action universially.

The force_dma_unencrypted() should only be done way up the call chain
where we decide to get a phys that is decrypted. Once we have a
decrypted phys it should be carried with an annotation throughout all
the other places.

Then this is more like:

if (flags & FLAG_DECRYPTED)
return phys_to_dma_unencrypted(dev, phys);

Jason