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

[Suzuki K Poulose]

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@xxxxxxx>
> > Cc: David Hildenbrand (Arm) <david@xxxxxxxxxx>
> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> > ---
> > 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

>