Re: [RFC PATCH v2 3/5] dma-mapping: Decrypt memory on remap

[Jason Gunthorpe]

On Mon, Mar 30, 2026 at 02:50:41PM +0000, Mostafa Saleh wrote:

> @@ -265,6 +266,9 @@ void *dma_direct_alloc(struct device *dev, size_t size,
>  		set_uncached = false;
>  	}
>  
> +	if (dma_set_decrypted(dev, page_address(page), size))
> +		goto out_leak_pages;
> +
>  	if (remap) {
>  		pgprot_t prot = dma_pgprot(dev, PAGE_KERNEL, attrs);
>
>                if (force_dma_unencrypted(dev))
>                        prot = pgprot_decrypted(prot);

It seems confusing, why do we unconditionally call something called
dma_set_decrypted() and then conditionally call pgprot_decrypted()?

So, I think the same remark, lets not sprinkle these tests all over
the place and risk them becoming inconsistent. It should be much more
direct, like:

    page = __dma_direct_alloc_pages(dev, size, gfp & ~__GFP_ZERO,
				    allow_highmem, &flags);

    if (!dev_can_dma_from_encrypted(dev) && !(flags & FLAG_DECRYPTED)) {
       dma_set_decrypted(dev, page_address(page));
       flags = FLAG_DECRYPTED;
    }

    if (flags & FLAG_DECRYPTED)
       prot = pgprot_decrypted(prot);

And so on.

The one place we should see a force_dma_unencrypted() is directly
before setting the flag.

Jason