x86/hyperv: Properly suspend/resume reenlightenment notifications

Errors during hibernation with reenlightenment notifications enabled were
reported:

 [   51.730435] PM: hibernation entry
 [   51.737435] PM: Syncing filesystems ...
 ...
 [   54.102216] Disabling non-boot CPUs ...
 [   54.106633] smpboot: CPU 1 is now offline
 [   54.110006] unchecked MSR access error: WRMSR to 0x40000106 (tried to
     write 0x47c72780000100ee) at rIP: 0xffffffff90062f24
     native_write_msr+0x4/0x20)
 [   54.110006] Call Trace:
 [   54.110006]  hv_cpu_die+0xd9/0xf0
 ...

Normally, hv_cpu_die() just reassigns reenlightenment notifications to some
other CPU when the CPU receiving them goes offline. Upon hibernation, there
is no other CPU which is still online so cpumask_any_but(cpu_online_mask)
returns >= nr_cpu_ids and using it as hv_vp_index index is incorrect.
Disable the feature when cpumask_any_but() fails.

Also, as we now disable reenlightenment notifications upon hibernation we
need to restore them on resume. Check if hv_reenlightenment_cb was
previously set and restore from hv_resume().
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Dexuan Cui <decui@microsoft.com>
Reviewed-by: Tianyu Lan <Tianyu.Lan@microsoft.com>
Link: https://lore.kernel.org/r/20200512160153.134467-1-vkuznets@redhat.comSigned-off-by: Wei Liu <wei.liu@kernel.org>

arch/x86/hyperv/hv_init.c

@@ -226,10 +226,18 @@ static int hv_cpu_die(unsigned int cpu)
 
 	rdmsrl(HV_X64_MSR_REENLIGHTENMENT_CONTROL, *((u64 *)&re_ctrl));
 	if (re_ctrl.target_vp == hv_vp_index[cpu]) {
-		/* Reassign to some other online CPU */
+		/*
+		 * Reassign reenlightenment notifications to some other online
+		 * CPU or just disable the feature if there are no online CPUs
+		 * left (happens on hibernation).
+		 */
 		new_cpu = cpumask_any_but(cpu_online_mask, cpu);
 
-		re_ctrl.target_vp = hv_vp_index[new_cpu];
+		if (new_cpu < nr_cpu_ids)
+			re_ctrl.target_vp = hv_vp_index[new_cpu];
+		else
+			re_ctrl.enabled = 0;
+
 		wrmsrl(HV_X64_MSR_REENLIGHTENMENT_CONTROL, *((u64 *)&re_ctrl));
 	}
 
@@ -293,6 +301,13 @@ static void hv_resume(void)
 
 	hv_hypercall_pg = hv_hypercall_pg_saved;
 	hv_hypercall_pg_saved = NULL;
+
+	/*
+	 * Reenlightenment notifications are disabled by hv_cpu_die(0),
+	 * reenable them here if hv_reenlightenment_cb was previously set.
+	 */
+	if (hv_reenlightenment_cb)
+		set_hv_tscchange_cb(hv_reenlightenment_cb);
 }
 
 /* Note: when the ops are called, only CPU0 is online and IRQs are disabled. */