[RFC PATCH 1/3] arm64: kvm: Handle Asymmetric AArch32 systems

[James Morse]

Hi Marc,

On 13/10/2020 11:32, Marc Zyngier wrote:
> On 2020-10-12 16:32, James Morse wrote:
>> On 09/10/2020 13:48, Qais Yousef wrote:
>>> On 10/09/20 13:34, Marc Zyngier wrote:
>>>> You can try setting vcpu->arch.target to -1, which is already caught by
>>>> kvm_vcpu_initialized() right at the top of this function. This will
>>
>>>> prevent any reentry unless the VMM issues a KVM_ARM_VCPU_INIT ioctl.
>>
>> This doesn't reset SPSR, so this lets the VMM restart the guest with a
>> bad value.
> 
> That's not my reading of the code. Without a valid target, you cannot enter
> the guest (kvm_vcpu_initialized() prevents you to do so). To set the target,
> you need to issue a KVM_ARM_VCPU_INIT ioctl, which eventually calls

> kvm_reset_vcpu(), which does set PSTATE to something legal.

aha! So it does, this is what I was missing.


> Or do you mean the guest's SPSR_EL1? Why would that matter?
> 
>> I think we should make it impossible to return to aarch32 from EL2 on
>> these systems.
> 
> And I'm saying that the above fulfills that requirement. Am I missing
> something obvious?

Nope, I was.

I agree the check on entry from user-space isn't needed.


Thanks,

James