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

[Marc Zyngier <marc.zyngier@arm.com>]

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.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny.