On 2017-11-16 18:21, Paolo Bonzini wrote:
On 16/11/2017 06:06, Quan Xu wrote:
when vcpu thread is scheduled out, the pkru value in
current->thread.fpu.state may be the host pkru value, instead of
guest pkru value (of course, this _assumes_ that the pkru is in
current->thread.fpu.state as well). in this way, the pkru may be a
coner case.
Rik may correct me, but I think this is not possible. Preemption is
disabled all the time while PKRU = guest_pkru (which is only during
vmx_vcpu_run).
refer to the following code,
vcpu_enter_guest()
{
...
preempt_disable()
...
kvm_x86_ops->run(vcpu); (actually it is vmx_vcpu_run())
...
...
preempt_enable();
}
when preempt_disable before to run kvm_x86_ops->run..
in kvm_x86_ops->run, the pkru is restored with host_pkru (IF guest_pkru
!= host_pkru).
all this happened under preempt_disable().
it's not true that preemtion is disable all the time while PKRU =
guest_pkru..
However it seems there is still some gap..
as Rik said, "at context switch time, the context switch code will save
the guest
FPU state to current->thread.fpu when the VCPU thread is scheduled out."
after preempt_enable() in vcpu_enter_guest(), the vcpu thread is
scheduled out,
in kvm_x86_ops->run, the PKRU has been restored with host_pkru (IF
guest_pkru != host_pkru)..
instead of guest_pkru..
then the PKRU is host_pkru, how to save guest_pkru current->thread.fpu?
as mentioned, all this _assumes_ that the pkru is in
current->thread.fpu.state as well.
thanks,
Quan
Alibaba Cloud
Context switching will only happen in vcpu_enter_guest() after
preempt_enable() for a preemptible kernel, or in vcpu_run via
cond_resched() for a non-preemptible kernel.
Thanks,
Paolo
VM migration again, in case,
source_host_pkru_value != guest_pkru_value,
target_host_pkru_value == guest_pkru_value..
the pkru status would be inconsistent..
