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

[Samiullah Khawaja <skhawaja@google.com>]

On Mon, Jun 01, 2026 at 01:35:16PM +0100, Will Deacon wrote:
>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?

Agreed. So basically return error if the range belongs to one of the
CMAs. I will update this.
>
>Will