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

Christoffer Dall
2017-10-26T15:28:28Z

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?

Thanks,
-Christoffer

> +
> ret = vgic_its_save_ite(its, device, ite, gpa, ite_esz);
> if (ret)
> return ret;
> --
> 2.14.1
>
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