Re: [PATCH v4 23/26] KVM: arm/arm64: GICv4: Prevent a VM using GICv4 from being saved

Christoffer Dall
2017-10-30T06:48:16Z

On Fri, Oct 27, 2017 at 02:56:10PM +0100, Marc Zyngier wrote:
> On Thu, Oct 26 2017 at 5:28:28 pm BST, Christoffer Dall <cdall@linaro.org> wrote:
> > On Fri, Oct 06, 2017 at 04:33:58PM +0100, Marc Zyngier wrote:
> >> The GICv4 architecture doesn't make it easy for save/restore to
> >> work, as it doesn't give any guarantee that the pending state
> >> is written into the pending table.
> >>
> >> So let's not take any chance, and let's return an error if
> >> we encounter any LPI that has the HW bit set.
> >>
> >> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> >> ---
> >> virt/kvm/arm/vgic/vgic-its.c | 9 +++++++++
> >> 1 file changed, 9 insertions(+)
> >>
> >> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
> >> index f434748439ee..01aa4d9d405e 100644
> >> --- a/virt/kvm/arm/vgic/vgic-its.c
> >> +++ b/virt/kvm/arm/vgic/vgic-its.c
> >> @@ -1987,6 +1987,15 @@ static int vgic_its_save_itt(struct vgic_its *its, struct its_device *device)
> >> list_for_each_entry(ite, &device->itt_head, ite_list) {
> >> gpa_t gpa = base + ite->event_id * ite_esz;
> >>
> >> + /*
> >> + * If an LPI carries the HW bit, this means that this
> >> + * interrupt is controlled by GICv4, and we do not
> >> + * have direct access to that state. Let's simply fail
> >> + * the save operation...
> >> + */
> >> + if (ite->irq->hw)
> >> + return -EINVAL;
> >
> > Will this conflict with other error messages, and will QEMU have a
> > reasonable way to tell the user what's going on?
> >
> > Perhaps we shoul document the return code in the ITS device doc and
> > choose something unique, like -EBUSY?
>
> Yup. I've now switched to -EACCES, which is probably the least horrible
> among the error codes we're not using yet. I've also amended the
> documentation to that effect.
>

Sounds good. -EJUSTANUMBER.

Thanks,
-Christoffer