Re: [PATCH v2] memblock: don't allocate new reserve_mem regions on a KHO boot

["Jose A. Perez de Azpillaga" <azpijr@gmail.com>]

On 11/5/26 8:59 AM, Mike Rapoport wrote:
> On Wed, Nov 04, 2026 at 09:42:17PM +0100, Jose A. Perez de Azpillaga wrote:
>> On a KHO boot, a reserve_mem region that can't be revived is allocated
>> from KHO_NOPRSRV memory, which includes the bootmem the next kernel
>> boots out of. With CONFIG_KEXEC_HANDOVER_DEBUG, preserving the region
>> then fails:
>>
>>   WARNING: kernel/liveupdate/kexec_handover.c:1245 at kho_preserve_pages+0x168/0x180
>>   failed to prepare memblock FDT for KHO: -22
>>
>> Without it, the next kernel puts its memmap on top of the region and
>> the ramoops records in it are lost.
>>
>> There is no use case for adding regions across a live update, so fail
>> instead of allocating, and drop the TODO.
>>
>> Fixes: f99230780211 ("memblock: add KHO support for reserve_mem")
>> Signed-off-by: Jose A. Perez de Azpillaga <azpijr@gmail.com>
>> ---
>> Changes in v2:
>> - fail on a KHO boot instead of allocating outside bootmem, as agreed
>>   with Pratyush [1]. this drops v1's patch 1.
>> - not an RFC anymore.
>> - based on v7.4-rc1.
>>
>> v1: https://lore.kernel.org/all/20261021211058.83483-3-azpijr@gmail.com/
>>
>> [1] https://lore.kernel.org/all/2vxzfqxglrg6.fsf@kernel.org/
>>
>>  mm/memblock.c | 11 ++++++++++-
>>  1 file changed, 10 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/memblock.c b/mm/memblock.c
>> index a450092a80fb..e325e0542c9a 100644
>> --- a/mm/memblock.c
>> +++ b/mm/memblock.c
>> @@ -2827,7 +2827,16 @@ static int __init reserve_mem(char *p)
>>  	if (reserve_mem_kho_revive(name, size, align))
>>  		return 1;
>>  
>> -	/* TODO: Allocation must be outside of KHO_NOPRSRV region */
>> +	/*
>> +	 * On a KHO boot memblock only allocates from KHO_NOPRSRV memory here,
>> +	 * which includes the bootmem the next kernel boots out of. Only regions
>> +	 * handed over by the previous kernel are supported.
>> +	 */
>> +	if (is_kho_boot()) {
> 
> This breaks memblock tests, please add a stub there.


oops, sorry. will add it in v3 :)

-- 
cheers,
jose a. p-a