Re: [Qemu-devel] [PATCH] i386/kvm: Do not sync nested state during runtime

[Liran Alon]

> On 22 Jul 2019, at 13:20, Jan Kiszka <address@hidden> wrote:
> 
> On 22.07.19 11:44, Liran Alon wrote:
>> 
>> 
>>> On 22 Jul 2019, at 7:00, Jan Kiszka <address@hidden> wrote:
>>> 
>>> Writing the nested state e.g. after a vmport access can invalidate
>>> important parts of the kernel-internal state, and it is not needed as
>>> well. So leave this out from KVM_PUT_RUNTIME_STATE.
>>> 
>>> Suggested-by: Paolo Bonzini <address@hidden>
>>> Signed-off-by: Jan Kiszka <address@hidden>
>> 
>> As QEMU never modifies vCPU nested-state in userspace besides in vmload and 
>> vCPU creation,
>> shouldn’t this be under KVM_PUT_FULL_STATE? Same as the call to 
>> kvm_arch_set_tsc_khz().
> 
> Reset is a relevant modification as well. If we do not write back a state that
> is disabling virtualization, we break.
> 
> Jan

Currently QEMU writes to userspace maintained nested-state only at 
kvm_arch_init_vcpu() and
when loading vmstate_nested_state vmstate subsection.
kvm_arch_reset_vcpu() do not modify userspace maintained nested-state.

I would expect KVM internal nested-state to be reset as part of KVM’s 
vmx_vcpu_reset().
Are we missing a call to vmx_leave_nested() there? 

-Liran