context_tracking: Move guest exit vtime accounting to separate helpers

stable inclusion
from stable-5.10.41
commit 77068304b30f553b05934224146813d3cdcaa12c
bugzilla: 51890
CVE: NA

--------------------------------

commit 88d8220b 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>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Acked-by: Weilong Chen <chenweilong@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>