alpine-xen boot options

I've installed alpine linux xen onto a USB stick and have a nice working Dom0 which I'm happy with.

I'd like to pass dom0_max_vcpus=1 and dom0_vcpus_pin to the xen kernel but adding that as kernel parameters in syslinux.cfg does nothing.

kernel /boot/syslinux/mboot.c32
append /boot/xen.gz --- /boot/grsec alpine_dev=usbdisk:vfat modules=loop,squashfs,sd-mod,usb-storage modloop=/boot/grsec.modloop.squashfs nomodeset --- /boot/grsec.gz dom0_max_vcpus=1 dom0_vcpus_pin

and my /etc/xen/xen-config.sxp contains

(dom0-cpus 1)

Anything obvious that i'm doing wrong?

EDIT

dom0_max_vcpus=1 dom0_vcpus_pin options need to be the first options

/boot/grsec.gz dom0_max_vcpus=1 dom0_vcpus_pin --- /boot/grsec alpine_dev=usbdisk:vfat modules= etc