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

["David Hildenbrand (Arm)" <david@kernel.org>]

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.

-- 
Cheers,

David