[PATCH 1/3] OvmfPkg: Send EOI before RestoreTPL() in timer interrupt handlers

["Michael Brown" <mcb30@ipxe.org>]

Deferring the EOI until after the call to RestoreTPL() means that any
callbacks invoked by RestoreTPL() will run with timer interrupt
delivery disabled.  If any such callbacks themselves rely on timers to
implement timeout loops, then the callbacks will get stuck in an
infinite loop from which the system will never recover.

This reverts commit 239b50a86 ("OvmfPkg: End timer interrupt later to
avoid stack overflow under load").

Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=4162
Signed-off-by: Michael Brown <mcb30@ipxe.org>
---
 OvmfPkg/8254TimerDxe/Timer.c                  | 5 ++---
 OvmfPkg/LocalApicTimerDxe/LocalApicTimerDxe.c | 5 ++---
 2 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/OvmfPkg/8254TimerDxe/Timer.c b/OvmfPkg/8254TimerDxe/Timer.c
index e49a438b44..7feaaaba2b 100644
--- a/OvmfPkg/8254TimerDxe/Timer.c
+++ b/OvmfPkg/8254TimerDxe/Timer.c
@@ -80,6 +80,8 @@ TimerInterruptHandler (
 
   OriginalTPL = gBS->RaiseTPL (TPL_HIGH_LEVEL);
 
+  mLegacy8259->EndOfInterrupt (mLegacy8259, Efi8259Irq0);
+
   if (mTimerNotifyFunction != NULL) {
     //
     // @bug : This does not handle missed timer interrupts
@@ -88,9 +90,6 @@ TimerInterruptHandler (
   }
 
   gBS->RestoreTPL (OriginalTPL);
-
-  DisableInterrupts ();
-  mLegacy8259->EndOfInterrupt (mLegacy8259, Efi8259Irq0);
 }
 
 /**
diff --git a/OvmfPkg/LocalApicTimerDxe/LocalApicTimerDxe.c b/OvmfPkg/LocalApicTimerDxe/LocalApicTimerDxe.c
index cbc17c979c..3e04b49d6b 100644
--- a/OvmfPkg/LocalApicTimerDxe/LocalApicTimerDxe.c
+++ b/OvmfPkg/LocalApicTimerDxe/LocalApicTimerDxe.c
@@ -62,6 +62,8 @@ TimerInterruptHandler (
 
   OriginalTPL = gBS->RaiseTPL (TPL_HIGH_LEVEL);
 
+  SendApicEoi ();
+
   if (mTimerNotifyFunction != NULL) {
     //
     // @bug : This does not handle missed timer interrupts
@@ -70,9 +72,6 @@ TimerInterruptHandler (
   }
 
   gBS->RestoreTPL (OriginalTPL);
-
-  DisableInterrupts ();
-  SendApicEoi ();
 }
 
 /**
-- 
2.38.1