On Mon, Jul 16, 2018 at 03:06:26PM +0200, Christoffer Dall wrote: > Simply letting IGROUPR be writable from userspace would break > migration from old kernels to newer kernels, because old kernels > incorrectly report interrupt groups as group 1. This would not be a big > problem if userspace wrote GICD_IIDR as read from the kernel, because we > could detect the incompatibility and return an error to userspace. > Unfortunately, this is not the case with current userspace > implementations and simply letting IGROUPR be writable from userspace for > an emulated GICv2 silently breaks migration and causes the destination > VM to no longer run after migration. > > We now encourage userspace to write the read and expected value of > GICD_IIDR as the first part of a GIC register restore, and if we observe > a write to GICD_IIDR we know that userspace has been updated and has had > a chance to cope with older kernels (VGICv2 IIDR.Revision == 0) > incorrectly reporting interrupts as group 1, and therefore we now allow > groups to be user writable. > > Signed-off-by: Christoffer Dall <christoffer.dall@xxxxxxx> > --- > include/kvm/arm_vgic.h | 3 +++ > virt/kvm/arm/vgic/vgic-mmio-v2.c | 16 +++++++++++++++- > 2 files changed, 18 insertions(+), 1 deletion(-) > Reviewed-by: Andrew Jones <drjones@xxxxxxxxxx>
