Re: [net-next,v6 1/8] octeontx2-pf: map skb data as device writeable

[Bharat Bhushan]

On Wed, Aug 21, 2024 at 4:06 AM Jakub Kicinski <kuba@xxxxxxxxxx> wrote:
>
> On Mon, 19 Aug 2024 17:53:41 +0530 Bharat Bhushan wrote:
> > Crypto hardware need write permission for in-place encrypt
> > or decrypt operation on skb-data to support IPsec crypto
> > offload. So map this memory as device read-write.
>
> How do you know the fragments are not read only?

IOMMU permission faults will be reported if the DMA_TO_DEVICE direction flag
is used in dma_map_page_attrs(). This is because iommu creates read only mapping
if the DMA_TO_DEVICE direction flag is used.  If the direction flag used in
dma_map_pages() is DMA_BIDIRECTIONAL then iommu creates mapping with
both read and write permission.

>
> (Whatever the answer is it should be part of the commit msg)

Will update commit message to something like:

Crypto hardware needs both read and write permission for in-place
encryption/decryption operation. Iommu creates read only mapping
if the DMA_TO_DEVICE direction flag is used in dma_map_page_attrs().
Use DMA_BIDIRECTIONAL direction flag in dma_map_page_attrs(), so
that iommu mapping is created with both read and write permission.

Is that okay?

Thanks
-Bharat