mshv: Use common "entry virt" APIs to do work in root before running guest

Use the kernel's common "entry virt" APIs to handle pending work prior to
(re)entering guest mode, now that the virt APIs don't have a superfluous
dependency on KVM.

No functional change intended.

Signed-off-by: Sean Christopherson <[e-mail]>
Tested-by: Nuno Das Neves <[e-mail]>
Reviewed-by: Nuno Das Neves <[e-mail]>
Signed-off-by: Wei Liu <[e-mail]>

drivers/hv/Kconfig

···
 	# no particular order, making it impossible to reassemble larger pages
 	depends on PAGE_SIZE_4KB
 	select EVENTFD
+	select VIRT_XFER_TO_GUEST_WORK
 	default n
 	help
 	  Select this option to enable support for booting and running as root

drivers/hv/mshv.h

···
 int hv_call_get_partition_property(u64 partition_id, u64 property_code,
 				   u64 *property_value);
 
-int mshv_do_pre_guest_mode_work(ulong th_flags);
-
 #endif /* _MSHV_H */

drivers/hv/mshv_common.c

···
 	return 0;
 }
 EXPORT_SYMBOL_GPL(hv_call_get_partition_property);
-
-/*
- * Handle any pre-processing before going into the guest mode on this cpu, most
- * notably call schedule(). Must be invoked with both preemption and
- * interrupts enabled.
- *
- * Returns: 0 on success, -errno on error.
- */
-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 | _TIF_NEED_RESCHED_LAZY))
-		schedule();
-
-	if (th_flags & _TIF_NOTIFY_RESUME)
-		resume_user_mode_work(NULL);
-
-	return 0;
-}
-EXPORT_SYMBOL_GPL(mshv_do_pre_guest_mode_work);

drivers/hv/mshv_root_main.c

···
  * Authors: Microsoft Linux virtualization team
  */
 
+#include <linux/entry-virt.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/fs.h>
···
 	return 0;
 }
 
-static int mshv_pre_guest_mode_work(struct mshv_vp *vp)
-{
-	const ulong work_flags = _TIF_NOTIFY_SIGNAL | _TIF_SIGPENDING |
-				 _TIF_NEED_RESCHED  | _TIF_NEED_RESCHED_LAZY |
-				 _TIF_NOTIFY_RESUME;
-	ulong th_flags;
-
-	th_flags = read_thread_flags();
-	while (th_flags & work_flags) {
-		int ret;
-
-		/* nb: following will call schedule */
-		ret = mshv_do_pre_guest_mode_work(th_flags);
-
-		if (ret)
-			return ret;
-
-		th_flags = read_thread_flags();
-	}
-
-	return 0;
-}
-
 /* Must be called with interrupts enabled */
 static long mshv_run_vp_with_root_scheduler(struct mshv_vp *vp)
 {
···
 		u32 flags = 0;
 		struct hv_output_dispatch_vp output;
 
-		ret = mshv_pre_guest_mode_work(vp);
-		if (ret)
-			break;
+		if (__xfer_to_guest_mode_work_pending()) {
+			ret = xfer_to_guest_mode_handle_work();
+			if (ret)
+				break;
+		}
 
 		if (vp->run.flags.intercept_suspend)
 			flags |= HV_DISPATCH_VP_FLAG_CLEAR_INTERCEPT_SUSPEND;