KVM: x86: Defer vtime accounting 'til after IRQ handling

KVM: x86: Defer vtime accounting 'til after IRQ handling

commit 160457140187c5fb127b844e5a85f87f00a01b14 upstream.

Defer the call to account guest time until after servicing any IRQ(s)
that happened in the guest or immediately after VM-Exit.  Tick-based
accounting of vCPU time relies on PF_VCPU being set when the tick IRQ
handler runs, and IRQs are blocked throughout the main sequence of
vcpu_enter_guest(), including the call into vendor code to actually
enter and exit the guest.

This fixes a bug where reported guest time remains '0', even when
running an infinite loop in the guest:

  https://bugzilla.kernel.org/show_bug.cgi?id=209831

Fixes: 87fa7f3e98a131 ("x86/kvm: Move context tracking where it belongs")
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Co-developed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20210505002735.1684165-4-seanjc@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>