Re: [PATCH 02/12] kho: store incoming radix tree in kho_in

[Pratyush Yadav <pratyush@kernel.org>]

On Mon, May 11 2026, Mike Rapoport wrote:

> On Wed, Apr 29, 2026 at 03:39:04PM +0200, Pratyush Yadav wrote:
>> From: "Pratyush Yadav (Google)" <pratyush@kernel.org>
>> 
>> This allows other functions to also use the radix tree. While at it,
>> also use kho_get_mem_map_phys() instead of duplicating the code to get
>> the radix tree root from the FDT.
>> 
>> Signed-off-by: Pratyush Yadav (Google) <pratyush@kernel.org>
>> ---
>>  kernel/liveupdate/kexec_handover.c | 27 ++++++++-------------------
>>  1 file changed, 8 insertions(+), 19 deletions(-)
>> 
>> diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
>> index ba568d34c5b4..5758dc6fab5d 100644
>> --- a/kernel/liveupdate/kexec_handover.c
>> +++ b/kernel/liveupdate/kexec_handover.c
>> @@ -1294,6 +1294,7 @@ struct kho_in {
>>  	char previous_release[__NEW_UTS_LEN + 1];
>>  	u32 kexec_count;
>>  	struct kho_debugfs dbg;
>> +	struct kho_radix_tree radix_tree;
>>  };
>>  
>>  static struct kho_in kho_in = {
>> @@ -1373,24 +1374,10 @@ EXPORT_SYMBOL_GPL(kho_retrieve_subtree);
>>  
>>  static int __init kho_mem_retrieve(const void *fdt)
>>  {
>> -	struct kho_radix_tree tree;
>> -	const phys_addr_t *mem;
>> -	int len;
>> -
>> -	/* Retrieve the KHO radix tree from passed-in FDT. */
>> -	mem = fdt_getprop(fdt, 0, KHO_FDT_MEMORY_MAP_PROP_NAME, &len);
>> -
>> -	if (!mem || len != sizeof(*mem)) {
>> -		pr_err("failed to get preserved KHO memory tree\n");
>> -		return -ENOENT;
>> -	}
>> -
>> -	if (!*mem)
>> -		return -EINVAL;
>> -
>> -	tree.root = phys_to_virt(*mem);
>> -	mutex_init(&tree.lock);
>> -	return kho_radix_walk_tree(&tree, kho_preserved_memory_reserve);
>> +	kho_in.radix_tree.root = phys_to_virt(kho_get_mem_map_phys(fdt));
>
> Do we really want to remove an explicit check for 0 and get a WARN() in
> kho_radix_walk_tree()?

If mem_map_phys is 0 then kho_populate() never sets kho_in.scratch_phys
and thus kho_mem_retrieve() never gets called. So here it will never be
0, and if it is, a WARN() is certainly warranted.

Perhaps I should add a comment since this isn't so obvious?

>
>> +	mutex_init(&kho_in.radix_tree.lock);
>> +	return kho_radix_walk_tree(&kho_in.radix_tree,
>> +				   kho_preserved_memory_reserve);
>>  }
>>  
>>  static __init int kho_out_fdt_setup(void)
>> @@ -1597,8 +1584,10 @@ void __init kho_memory_init(void)
>>  	if (kho_in.scratch_phys) {
>>  		kho_scratch = phys_to_virt(kho_in.scratch_phys);
>>  
>> -		if (kho_mem_retrieve(kho_get_fdt()))
>> +		if (kho_mem_retrieve(kho_get_fdt())) {
>>  			kho_in.fdt_phys = 0;
>> +			kho_in.radix_tree.root = NULL;
>
> I'd make kho_mem_retrieve() void and put these there.

Sure, will do.

>
>> +		}
>>  	} else {
>>  		kho_reserve_scratch();
>>  	}
>> -- 
>> 2.54.0.545.g6539524ca2-goog
>> 

-- 
Regards,
Pratyush Yadav