[PATCH] x86/suspend: unconditionally raise a timer softirq on resume

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

The current code to restore the timer state on resume is incomplete.  While
the local APIC Initial Count Register is saved and restored across
suspension (even if possibly no longer accurate since it's not adjusted to
account for the time spent in suspension), the TSC deadline MSR is not
saved and restored, hence hosts using the TSC deadline timer will likely
get stuck when resuming from suspension.

The lack of restoring of the TSC deadline MSR was mitigated by the raising
of a timer softirq in mwait_idle_with_hints() if the timer had expired,
previous to commit 3faf0866a33070b926ab78e6298290403f85e76c, which removed
that logic.

This patch fixes the usage of the TSC deadline timer with suspension, by
unconditionally raising a timer softirq on resume, that will take care of
rearming the hardware timer.  Given that a timer softirq will be
unconditionally risen, there's no need to save and restore the APIC Initial
Count Register anymore either.

Note that secondary processors don't need this special treatment when
resuming, since they are offlined before suspension and brought back up
during resume, the first timer that gets setup will trigger a timer softirq
unconditionally, for example from sched_migrate_timers() that gets called
for each secondary processor.

Reported-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
Fixes: fd1291a826e1 ('X86: Prefer TSC-deadline timer in Xen')
Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/arch/x86/acpi/power.c | 2 ++
 xen/arch/x86/apic.c       | 3 ---
 2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/acpi/power.c b/xen/arch/x86/acpi/power.c
index 2ac162c997fe..27d672ad5dbb 100644
--- a/xen/arch/x86/acpi/power.c
+++ b/xen/arch/x86/acpi/power.c
@@ -19,6 +19,7 @@
 #include <xen/iommu.h>
 #include <xen/param.h>
 #include <xen/sched.h>
+#include <xen/softirq.h>
 #include <xen/spinlock.h>
 #include <xen/watchdog.h>
 
@@ -310,6 +311,7 @@ static int enter_state(u32 state)
     thaw_domains();
     system_state = SYS_STATE_active;
     spin_unlock(&pm_lock);
+    raise_softirq(TIMER_SOFTIRQ);
     return error;
 }
 
diff --git a/xen/arch/x86/apic.c b/xen/arch/x86/apic.c
index cac5ba39e615..e3a2b84f1aae 100644
--- a/xen/arch/x86/apic.c
+++ b/xen/arch/x86/apic.c
@@ -65,7 +65,6 @@ static struct {
     unsigned int apic_lvt0;
     unsigned int apic_lvt1;
     unsigned int apic_lvterr;
-    unsigned int apic_tmict;
     unsigned int apic_tdcr;
     unsigned int apic_thmr;
 } apic_pm_state;
@@ -658,7 +657,6 @@ int lapic_suspend(void)
     apic_pm_state.apic_lvt0 = apic_read(APIC_LVT0);
     apic_pm_state.apic_lvt1 = apic_read(APIC_LVT1);
     apic_pm_state.apic_lvterr = apic_read(APIC_LVTERR);
-    apic_pm_state.apic_tmict = apic_read(APIC_TMICT);
     apic_pm_state.apic_tdcr = apic_read(APIC_TDCR);
     if (maxlvt >= 5)
         apic_pm_state.apic_thmr = apic_read(APIC_LVTTHMR);
@@ -718,7 +716,6 @@ int lapic_resume(void)
         apic_write(APIC_LVTPC, apic_pm_state.apic_lvtpc);
     apic_write(APIC_LVTT, apic_pm_state.apic_lvtt);
     apic_write(APIC_TDCR, apic_pm_state.apic_tdcr);
-    apic_write(APIC_TMICT, apic_pm_state.apic_tmict);
     apic_write(APIC_ESR, 0);
     apic_read(APIC_ESR);
     apic_write(APIC_LVTERR, apic_pm_state.apic_lvterr);
-- 
2.49.0