[RFC PATCH 3/4] dma-direct: Add API to preserve/restore allocations

[Will Deacon]

On Tue, May 05, 2026 at 12:27:36AM +0000, Samiullah Khawaja wrote:
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index ec887f443741..c2b98f91900a 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -6,6 +6,8 @@
>   */
>  #include <linux/memblock.h> /* for max_pfn */
>  #include <linux/export.h>
> +#include <linux/kexec_handover.h>
> +#include <linux/kho/abi/dma_alloc.h>
>  #include <linux/mm.h>
>  #include <linux/dma-map-ops.h>
>  #include <linux/scatterlist.h>
> @@ -307,6 +309,167 @@ void *dma_direct_alloc(struct device *dev, size_t size,
>  	return NULL;
>  }
>  
> +#ifdef CONFIG_DMA_LIVEUPDATE
> +int dma_direct_preserve_allocation(struct device *dev, void *cpu_addr,
> +				   size_t size, dma_addr_t dma_handle,
> +				   unsigned long attrs, u64 *state)
> +{
> +	struct dma_alloc_ser *ser;
> +	int ret;
> +
> +	if (!kho_is_enabled())
> +		return -EOPNOTSUPP;
> +
> +	if (IS_ENABLED(CONFIG_DMA_CMA))
> +		return -EOPNOTSUPP;

Hmm, it seems a bit overkill to do this just because CMA is compiled
in, especially as it's user-selectable in kconfig.

Maybe you need to iterate over the CMA areas using cma_for_each_area(),
similarly to how you do with the pools?

Will