context_tracking: Move guest exit vtime accounting to separate helpers

context_tracking: Move guest exit vtime accounting to separate helpers

commit 88d8220bbf06dd8045b2ac4be1046290eaa7773a upstream.

Provide separate vtime accounting functions for guest exit instead of
open coding the logic within the context tracking code.  This will allow
KVM x86 to handle vtime accounting slightly differently when using
tick-based accounting.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Co-developed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Link: https://lore.kernel.org/r/20210505002735.1684165-3-seanjc@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>