mshv: Handle NEED_RESCHED_LAZY before transferring to guest

Check for NEED_RESCHED_LAZY, not just NEED_RESCHED, prior to transferring
control to a guest.  Failure to check for lazy resched can unnecessarily
delay rescheduling until the next tick when using a lazy preemption model.

Note, ideally both the checking and processing of TIF bits would be handled
in common code, to avoid having to keep three separate paths synchronized,
but defer such cleanups to the future to keep the fix as standalone as
possible.

Cc: Nuno Das Neves <nunodasneves@linux.microsoft.com>
Cc: Mukesh R <mrathor@linux.microsoft.com>
Fixes: 621191d ("Drivers: hv: Introduce mshv_root module to expose /dev/mshv to VMMs")
Signed-off-by: Sean Christopherson <seanjc@google.com>
Tested-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>
Reviewed-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>

Author: sean-jc

drivers/hv/mshv_common.c

@@ -151,7 +151,7 @@ int mshv_do_pre_guest_mode_work(ulong th_flags)
 	if (th_flags & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))
 		return -EINTR;
 
-	if (th_flags & _TIF_NEED_RESCHED)
+	if (th_flags & (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY))
 		schedule();
 
 	if (th_flags & _TIF_NOTIFY_RESUME)

drivers/hv/mshv_root_main.c

@@ -484,7 +484,8 @@ mshv_vp_wait_for_hv_kick(struct mshv_vp *vp)
 static int mshv_pre_guest_mode_work(struct mshv_vp *vp)
 {
 	const ulong work_flags = _TIF_NOTIFY_SIGNAL | _TIF_SIGPENDING |
-				 _TIF_NEED_RESCHED  | _TIF_NOTIFY_RESUME;
+				 _TIF_NEED_RESCHED  | _TIF_NEED_RESCHED_LAZY |
+				 _TIF_NOTIFY_RESUME;
 	ulong th_flags;
 
 	th_flags = read_thread_flags();