Re: [RFC PATCH 3/3] KVM: x86: Use KVM_BUG/KVM_BUG_ON to handle bugs that are fatal to the VM

Paolo Bonzini
2020-09-25T21:06:18Z

On 25/09/20 19:12, Sean Christopherson wrote:
>> Do we actually want to prevent *all* ioctls? E.g. when 'vm bugged'
>> condition is triggered userspace may want to extract some information to
>> assist debugging but even things like KVM_GET_[S]REGS will just return
>> -EIO. I'm not sure it is generally safe to enable *everything* (except
>> for KVM_RUN which should definitely be forbidden) so maybe your approach
>> is preferable.
>
> The answer to this probably depends on the answer to the first question of
> when it's appropriate to use KVM_BUG(). E.g. if we limit usage to fatal or
> dangrous cases, then blocking all ioctls() is probably the right thing do do.

I think usage should be limited to dangerous cases, basically WARN_ON
level. However I agree with Vitaly that KVM_GET_* should be allowed.

The other question is whether to return -EIO or KVM_EXIT_INTERNAL_ERROR.
The latter is more likely to be handled already by userspace.

Paolo