OvmfPkg: End timer interrupt later to avoid stack overflow under load
RestoreTPL called while at TPL_HIGH_LEVEL unconditionally enables
interrupts even if called in interrupt handler. That opens a window while
interrupt is not completely handled but another interrupt could be
accepted.
If a VM starts on a heavily loaded host hundreds of periodic timer
interrupts might be queued while vCPU is descheduled (the behavior is
typical for a Xen host). The next time vCPU is scheduled again all of them
get delivered back to back causing OVMF to accept each one without
finishing a previous one and cleaning up the stack. That quickly results
in stack overflow and a triple fault.
Fix it by postponing sending EOI until we finished processing the current
tick giving interrupt handler opportunity to clean up the stack before
accepting the next tick.
Signed-off-by: Igor Druzhinin <igor.druzhinin@citrix.com>
Message-Id: <1592275782-9369-1-git-send-email-igor.druzhinin@citrix.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=2815
Acked-by: Laszlo Ersek <lersek@redhat.com>
[lersek@redhat.com: add BZ ref; rewrap msg to silence PatchCheck.py]
diff --git a/OvmfPkg/8254TimerDxe/Timer.c b/OvmfPkg/8254TimerDxe/Timer.c
index 67e22f5..fd1691b 100644
--- a/OvmfPkg/8254TimerDxe/Timer.c
+++ b/OvmfPkg/8254TimerDxe/Timer.c
@@ -79,8 +79,6 @@
OriginalTPL = gBS->RaiseTPL (TPL_HIGH_LEVEL);
- mLegacy8259->EndOfInterrupt (mLegacy8259, Efi8259Irq0);
-
if (mTimerNotifyFunction != NULL) {
//
// @bug : This does not handle missed timer interrupts
@@ -89,6 +87,9 @@
}
gBS->RestoreTPL (OriginalTPL);
+
+ DisableInterrupts ();
+ mLegacy8259->EndOfInterrupt (mLegacy8259, Efi8259Irq0);
}
/**
diff --git a/OvmfPkg/XenTimerDxe/XenTimerDxe.c b/OvmfPkg/XenTimerDxe/XenTimerDxe.c
index 9f9e047..0bec593 100644
--- a/OvmfPkg/XenTimerDxe/XenTimerDxe.c
+++ b/OvmfPkg/XenTimerDxe/XenTimerDxe.c
@@ -61,8 +61,6 @@
OriginalTPL = gBS->RaiseTPL (TPL_HIGH_LEVEL);
- SendApicEoi();
-
if (mTimerNotifyFunction != NULL) {
//
// @bug : This does not handle missed timer interrupts
@@ -71,6 +69,9 @@
}
gBS->RestoreTPL (OriginalTPL);
+
+ DisableInterrupts ();
+ SendApicEoi ();
}
/**
