Re: [PATCH v20 9/9] firmware: arm_rmm: hotplug: Skip memory added to ZONE_MOVABLE

[Suzuki K Poulose <suzuki.poulose@arm.com>]

On 30/09/2026 13:22, David Hildenbrand (Arm) wrote:
> On 9/30/26 00:16, Suzuki K Poulose wrote:
>> If the hotadded memory is in ZONE_MOVABLE, we could allow that to proceed
>> without the RMM having fine grained tracking, as we won't allocate pages
>> from there for guest-memfd or kernel allocation
>>
>> Cc: Catalin Marinas <catalin.marinas@arm.com>
>> Cc: David Hildenbrand (Arm) <david@kernel.org>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
>> ---
>> Changes since v19:
>>   - New patch in v20, keeping this at the tail to allow for the rest of the
>>     series to proceed, while this patch gets discussed.
>> ---
>>   drivers/firmware/arm_rmm/rmi.c | 12 ++++++++++++
>>   1 file changed, 12 insertions(+)
>>
>> diff --git a/drivers/firmware/arm_rmm/rmi.c b/drivers/firmware/arm_rmm/rmi.c
>> index d4d098448e46e..ef0a171ba9677 100644
>> --- a/drivers/firmware/arm_rmm/rmi.c
>> +++ b/drivers/firmware/arm_rmm/rmi.c
>> @@ -1043,6 +1043,18 @@ static int rmi_memory_notifier(struct notifier_block *nb,
>>   	start = PFN_PHYS(arg->start_pfn);
>>   	end = PFN_PHYS(arg->start_pfn + arg->nr_pages);
>>   
>> +	/*
>> +	 * If the hotplugged memory region is in ZONE_MOVABLE, neither the
>> +	 * guest-memfd nor the kernel allocations can come from there. So we are
>> +	 * fine to skip this.
>> +	 * For boot time memory, we don't allow this discount, as the
>> +	 * decision to move boot memory pages to ZONE_MOVABLE is purely
>> +	 * a kernel choice and the firmware must have decided what it covers.
>> +	 */
>> +	if (page_zonenum(pfn_to_page(arg->start_pfn)) == ZONE_MOVABLE &&
>> +	    page_zonenum(pfn_to_page(arg->start_pfn + arg->nr_pages - 1)) == ZONE_MOVABLE)
>> +		return NOTIFY_DONE;
>> +
> 
> is_zone_movable_page(pfn_to_page(start_pfn)
> 
> as used by virtio-mem should be sufficient. Checking only the start pfn is
> sufficient.

Thanks David, I will update it.

Cheers
Suzuki

>